# Adding diesel fuel to gasohol to increase mileage/efficiency? **URL:** \ **Category:** Factual Questions\ **Created:** [January 7, 2010, 7:32pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055 "2010-01-07T19:32:06Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [January 9, 2010, 9:42pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/21 "2010-01-09T21:42:42Z")
> [@The\_Central\_Scrutinizer](#): > > 1. We also use TufOil, a PTFE-resin product added w/ every oil change. We’ve found it increases mileage, eases cold-engine cranking, reduces any oil burning, increases power & tends to quiet lifters or other odd taps & clatters. This product can also be used in power steering units, manual gearboxes, just about anywhere except automatic transmissions (it’s just too damn slippery!) > Oh, BTW, with the help of Fram’s tech staff & some spec review, I use the largest/longest oil filter version equivalent that will fit any particular application; for instance, instead of the stock filter in both the Saturn & the Kohler, I use the Fram PH3600-series (they both take the same size & the interior design being equivalent). This helps to increase the oil capacity, the filter-cooling effect, & increases the filtering area, further extending the oil-change intervals. As has been mentioned TufOil is generally considered to be snake oil at best. Secondly if you really care about you car consider changing to a different brand of filter. There are a number of site around the interwebs where people have cut filters apart and analyzed them for how they are built. Fram’s are not the best in these tests. > [@The\_Central\_Scrutinizer](#): > > Hence my plan of renting a similar economy car to my own… slowly increasing the % of diesel until I get unhappy indications, then topping up w/ gas before returning it. I consider this to be highly unethical, and frankly a scummy thing to contemplate. The only reason you are considering renting a car is in the event of a expensive repair bill, you can (you hope) duck out of it. If you want to experiment use your own damn equipment. If it the experiment fails and it costs you a ton of money, oh well. Since we are not in the pit, I cannot say more. Rick A guys who keeps a fleet of loan cars, and would be pissed if one of my customers tried this shit on one of my cars. ---
**Author:** ![TurboNuke](https://avatars.discourse-cdn.com/v4/letter/t/f19dbf/32.png) [@TurboNuke](https://boards.straightdope.com/u/TurboNuke)\ **Post date:** [January 10, 2010, 1:00am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/22 "2010-01-10T01:00:40Z")
Why would you think that adding diesel would get you better mileage? Diesel engines get better mileage cause they are designed differently. They can be designed differently because they use diesel fuel. Unless you redesign the engine to run with the new fuel you are providing I can see no possible benefit. Unless diesel is significantly cheaper where you are? ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 1:12am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/23 "2010-01-10T01:12:30Z")
> [@Wilbo523](#): > > Don’t be surprised when the rental car companies charge you for the damage you do their car when you put the incorrect fuel in it. All standard rental contracts stipulate that you put the correct fuel in the car. Actually, the last time I rented a truck to do some moving, it was gasoline-fueled. Is gasohol the same as gasoline? & if the vehicle I used started complaining, & I added gasohol to top the tank back up so that it stopped complaining, wouldn’t that, in effect, be the same? I’m not talking about dumping a tankful of the wrong fuel into a vehicle, any more than my fueling with a splash-blended fuel sourced from methanol or a water-contaminated underground fuel tank. The rental company also would much rather people didn’t run over curbs, slam on the brakes, spin wheels, slam the doors, do donuts in the parking lot, overload the vehicles, or exceed 45 MPH when towing. Any damage that might show up sometime later down the road might be regrettable, but that’s both a write-off & the nature of the business. Then the vehicles are sold, either to someone who knows full well that it’s probably already been abused “like a rented mule” or sold at auction with the same knowledge. If I were to strictly pay for the actual operating costs without adding to their profit margin, I’d be paying for a helluva lot less than what I already do. ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 10, 2010, 1:22am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/24 "2010-01-10T01:22:29Z")
> [@The\_Central\_Scrutinizer](#): > > The rental company also would much rather people didn’t run over curbs, slam on the brakes, spin wheels, slam the doors, do donuts in the parking lot, overload the vehicles, or exceed 45 MPH when towing. Any damage that might show up sometime later down the road might be regrettable, but that’s both a \*\*write-off \*\*& the nature of the business. . And Kramer on Seinfield used the write off excuse to justify stealing. With about as much believability. Experimenting with other people’s equipment is a shit thing to do. If you are SURE it won’t do damage, experiment with your own equipment and have fun. If you ARENT sure, keep you grubby hands off other peoples equipment. ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 1:29am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/25 "2010-01-10T01:29:09Z")
> [@Saintly\_Loser](#): > > Kerosene in a gas engine might burn lean – I don’t know what the right air/fuel mixture would be for a kerosene-burning piston engine - but your engine would likely be destroyed in short order by detonation, no matter what the pistons were made of. Yes, the same thing occurs when switching to 100% alcohol, if you’ve got a carbureted engine. Modern fuel injection engines have open-loop systems, & things like mass air-flow sensors, oxygen sensors, temperature sensors, knock sensors, etc. constantly provide feedback to the computer system modulating the fuel injection system to keep the ratio at the optimum level. In the days prior to such systems, the mileage was so poor as a result of less-than-optimum ratios being used in an attempt to minimize emissions… but that raised combustion temperatures, so NOx levels went up, so then they introduced EGR systems, which again lowered efficiency. When modern fuel injection was combined with competent & affordable electronics, the whole picture was greatly simplified, & the refineries could lower their standards, presenting an opportunity to use relative garbage as a fuel while still getting decent performance. Oxygen sensors were a necessary element, but they couldn’t tolerate the TEL in common usage, so, in conjunction with health concerns, its use was phased out. (In the countries where cocoa beans are grown, TEL is still in common usage; consequently, chocolate lovers face high levels of lead ingestion, for instance.) Now the fuel ratio is kept at its optimum for efficiency leaving the catalytic converter to finish the process, which is the reason they get so hot. That heat energy is totally wasted, however, but it’s better than getting 5-10 MPG. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [January 10, 2010, 1:39am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/26 "2010-01-10T01:39:25Z")
> [@The\_Central\_Scrutinizer](#): > > Actually, the last time I rented a truck to do some moving, it was gasoline-fueled. Is gasohol the same as gasoline? & if the vehicle I used started complaining, & I added gasohol to top the tank back up so that it stopped complaining, wouldn’t that, in effect, be the same? > > I’m not talking about dumping a tankful of the wrong fuel into a vehicle, any more than my fueling with a splash-blended fuel sourced from methanol or a water-contaminated underground fuel tank. The rental company also would much rather people didn’t run over curbs, slam on the brakes, spin wheels, slam the doors, do donuts in the parking lot, overload the vehicles, or exceed 45 MPH when towing. Any damage that might show up sometime later down the road might be regrettable, but that’s both a write-off & the nature of the business. Then the vehicles are sold, either to someone who knows full well that it’s probably already been abused “like a rented mule” or sold at auction with the same knowledge. If I were to strictly pay for the actual operating costs without adding to their profit margin, I’d be paying for a helluva lot less than what I already do. Wow, just wow. The difference between running over a curb and doing unseen damage to the fuel system is that if you bubble a tire or bend a rim the rental company will bang your credit card for the damage. You know damn well that if you do damage to the inside of the engine or fuel system you probably won’t get caught and charged. The fact that you don’t get caught does not make it right or ethical. To pretend otherwise is just a fantasy. ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 1:40am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/27 "2010-01-10T01:40:09Z")
> [@Saintly\_Loser](#): > > PTFE is a solid. Oil additive manufacturers usually market it suspended an oil-based liquid. Most mechanics regard PTFE products (Slick 50, TufOil, and the like) as snake oil which _at best_ will do no harm to an engine, but is likely to clog oil galleries and filters over time. > > Your other tips are quite sensible, though. Actually, PTFE _resin_ isn’t a solid at all, & is quite different from Teflon particles, which is what products like Slick 50 use. They will, indeed, precipitate out of solution & clog passages as well as break loose from their applied surfaces & get stuck in all the wrong places. PTFE is PolyTetraFlouroEthane, & still being in the uncatalyzed state, much like polyester resin is to cured fiberglass, is a liquid. I’ve been using it for years & contrary to the “snake-oil” nay-sayers, it has proved, _to me_, its value as it has to all those I’ve recommended it to. It also works great as a lock lube & a gun lube as well. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [January 10, 2010, 2:03am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/28 "2010-01-10T02:03:19Z")
The simple answer to why adding diesel fuel to your gasoline powered engine is octane. In a modern gas engine the PCM (computer) adds spark during the compression stroke at the optimum time to detonate the gas. The higher the octane, the better the fuel resists pre-detonation, that is exploding before the spark is added and before the piston has completed the compression stroke. Pre-detonation or ‘knocking’ can and will damage a gas engine over time. This is why high compression engines are recomended premium gas. Adding 10% ethanol and making what is sometimes called ‘gasahol’ actually increases the octane rating. The modern vehicle has knock sensors so that the PCM can adjust the timing of the spark to use a range of fuels of different octanes. Even so, knocking can still occur by using low octane in a high compression engine. \*\*Regular gas has a RON octane rating of 91 and an AKI octane of 87. \*\* Pre-detonation or knock will not only damage the gas engine but it will also burn dirty since the optimum compression was not reached. So you get an underperforming engine that is burning dirty and polluting. Diesel engines burn fuel based upon the fuel detonating on it’s own without a timed spark being added. The low octane of diesel is part of the basis for the engine design. **The RON octane rating of diesel is 15-25.** All you will accomplish by adding diesel to gas or gasahol is to reduce the octane rating below what the PCM can adjust for, resulting in an engine that will chug and smoke and cause damage, if it will even run long at all. Wiki link about octane: > **[Octane rating](https://en.wikipedia.org/wiki/Octane_rating)** > > An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates gasoline's capability against compression. > Whether or not a higher octane fuel improves or impairs an engine's p... ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 2:06am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/29 "2010-01-10T02:06:19Z")
> [@Dog80](#): > > As others have already mentioned, the performance of those PTFE based additives is questionable. Also, if it is so slippery how can you use it in a manual transmission? The synchromeshes require some friction to work. If they slip too much you’ll be grinding metal at every gear change. > > PTFE resin isn’t friction-free, it just reduces it quite a bit. I’ve never had a problem in any manual transmission, & when I use it in conjunction w/ a synthetic lube like Mobil 1, since it is much more lubricious & thermally stable, I can use a lighter weight & save the friction inherent in heavier lubes, especially when cold. Ever go to shift a manual gearbox using standard heavy lube when it’s really cold? I have, noting that it almost seems to be stuck in a semi-solid state before I can loosen it up. This obviously causes some stress, wear & friction, at least until some driving has warmed it up. Some modern, lighter-duty automotive gearboxes use standard ATF; here, as well, Mobil 1 offers a synthetic version & here as well the PTFE resin is a benefit. > > Does the cost savings of not using the wipers offset the cost of Rain-X? I doubt it. > > You missed my point, the additional benefit of seeing better out of _all_ windows, the harder it rains the better. Try it yourself. Crap, etc. doesn’t stick as easily, either. The windshield will need monthly -or so- applications due to the friction of the wipers & air, but the rest of the windows stay clear for at least 6 months at a time. We also use a Rain-X windshield wash to extend the direct hand applications. I came across Rain-X when working on offshore sportfishers; no wipers on their Mylar bimini covers! No need to send me a check, just be sure to thank me… > > Yes, but you are making the oil pump work harder. Also big filters make the oil pressure fluctuate more. Actually, not… the expanded filter surface area _reduces_ the oil pump load, especially when cold, & if you do your research on the design of the filter, some newer versions of older designs have anti-drainback valves which keep the oil in the filter & oil galleys after shutdown. Larger filter medium + lower viscosity oil base = quicker oil flow delivered upon cold startup, which is a main contributor of bearing wear until they get pressurized flow. Also, engines have pressure regulators, a few of them are adjustable; excess pressure is vented back to the pan. Another reason I use a PTFE resin, it lubes before the oil gets there. I’ve even installed oil system pre-lubers which pre-feed the oil system just prior to startup. Cheaper than an overhaul… especially when the engine’s tough to access (like in a motorhome or under the deck of a marine vessel). ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 2:10am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/30 "2010-01-10T02:10:43Z")
> [@jasonh300](#): > > Sorry, you didn’t specify hybrid (which the link I posted was to a non-hybrid Prius). Wasn’t even aware the Hybrid Prius was available yet in 2004. > > Anyway, I’ve seen a website that a local guy put up charting his mileage on a Hybrid Prius and when he first got it, he started out a about 30-40 MPG in the city, but adapted his driving style and now gets 60-70 MPG in it. The Toyota Prius was always a hybrid, even back in the mid-90s as a concept car. Didn’t think I had to specify “hybrid Prius”. It’s improved a lot since then! It was first available in the U.S. market in 2001. Look it up on Wikipedia, lots of info there. ---
**Author:** ![TurboNuke](https://avatars.discourse-cdn.com/v4/letter/t/f19dbf/32.png) [@TurboNuke](https://boards.straightdope.com/u/TurboNuke)\ **Post date:** [January 10, 2010, 2:21am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/31 "2010-01-10T02:21:00Z")
Again, why are you doing this? What do you think you are gaining by adding diesel to gas? ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 2:28am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/32 "2010-01-10T02:28:31Z")
> [@TurboNuke](#): > > Why would you think that adding diesel would get you better mileage? > > Diesel engines get better mileage cause they are designed differently. They can be designed differently because they use diesel fuel. Unless you redesign the engine to run with the new fuel you are providing I can see no possible benefit. Unless diesel is significantly cheaper where you are? My thought that diesel fuel might offset the effects of alcohol addition to the gasoline fuel supply is based on the fact that alcohol in gasoline reduces fuel mileage as a function of its lower BTU content. As I stated before, we have quite an accurate means of determining on record of that fact. Diesel has a higher BTU content. I’m not proposing running a gasoline engine on diesel (GM learned the hard way that it wouldn’t work) but merely trying to determine the optimum % of diesel to be added to gasohol to regain the mileage lost due to the alcohol. I know full well the design differences between diesel & gasoline engines (specifically, spark vs. compression ignition) & the number of reasons that diesels are more efficient, amongst those being the 2-3X compression ratios, lack of a throttle, no pumping losses, controlled combustion process as a function of the injection duration (which is why they clatter while @ idle but not under load) etc. Diesel engines _require_ a different design, it’s not a matter of choice. Diesel is ~20-30 cents/gal more in our area, but that’s on-road diesel; off-road (dyed red) is cheaper as it’s not road-taxed. Any red dye that might show up on a random inspection of an on-road diesel-fueled vehicle would neither be evident in the minor % I’m considering or suspected in what would normally be regarded as a gasohol-fueled vehicle. Alcohol is both more expensive _&_ less fuel-efficient, not to mention contributes to more engine carbon buildup, yet both the Establishment & most “P-C” public seem perfectly comfortable with living with the consequences. I’m not “P-C”. Sorry, Sheeple. ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 2:48am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/33 "2010-01-10T02:48:45Z")
> [@Rick](#): > > Wow, just wow. The difference between running over a curb and doing unseen damage to the fuel system is that if you bubble a tire or bend a rim the rental company will bang your credit card for the damage. You know damn well that if you do damage to the inside of the engine or fuel system you probably won’t get caught and charged. The fact that you don’t get caught does not make it right or ethical. To pretend otherwise is just a fantasy. Think of it as a matter of national security, & doing it for the children. Both of those excuses almost always work when proposing otherwise unethical/unpopular ideas. If exploring the edge of conventional wisdom might save the environment & our country’s economic status by reducing the fuel consumption of our largest oil consumers, the automobile sector, it seems to be my Patriotic duty, doesn’t it? Is it any more “right” or “ethical” to force us to use what’s already known is a more damaging & less efficient fuel source while at the same time charging us more for it? Did you know, for instance, that some states like Oregon actually tax a hybrid owner more simply because they use less fuel, reducing their tax revenues? How ethical is that? Go write a letter to your congressman. If you were to consider the benefit of switching over to a totally home-grown fuel source like 100% ethanol (the technology’s already here, right now!) why not do it? Because the Establishment & Staus-Quo already have too much invested in designing & forcing us to buy vehicles which are “addicted” by design to only 1 fuel source… the key to energy independence is not to make vehicles that get 100, or a 1000MPG, the price of fuel will just go up. The key is to explore ideas supporting flexible fuel sources, whichever is available at the best price on the bidding market. As it is now, you can, indeed, brew your own alcohol fuel… once you buy your own equipment _&_ get a BATF permit. Then, try to modify the vehicle… so, lets explore. Look, I’m not asking your permission or approval, just some information. If you don’t approve, go have a beer (“whine”?) instead & don’t respond. Oh, BTW, you didn’t mention the wheel-spinning, door-slamming, overloading, donuts-in-the-parking-lot crowd. Do you think there’s any benefit to be found there, or that they’re any more righteous? Find a shorter horse. ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 2:51am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/34 "2010-01-10T02:51:53Z")
> [@jasonh300](#): > > No, they’re not, or at least, not always. I had a U-Haul truck several years ago that had the small filler hole, and I completely missed the giant letters on the side of the truck that said UNLEADED FUEL ONLY and pumped about 5 gallons of diesel before I realized what I was doing. Mixed with 25 gallons of unleaded, it ran fine, but the exhaust had a light diesel smoky smell. Thank You. BTW, how was the mileage? This is the kind of positive, informative response I appreciate! ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 10, 2010, 3:01am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/35 "2010-01-10T03:01:20Z")
> [@The\_Central\_Scrutinizer](#): > > Think of it as a matter of national security, & doing it for the children. . Dick Cheney… Is that you? Experiment on your own vehicle. ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 3:06am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/36 "2010-01-10T03:06:59Z")
> [@Rick](#): > > As has been mentioned TufOil is generally considered to be snake oil at best. > Secondly if you really care about you car consider changing to a different brand of filter. There are a number of site around the interwebs where people have cut filters apart and analyzed them for how they are built. Fram’s are not the best in these tests. > > I guess it depends on how they’re rated, on single-pass efficiency vs. multi-pass. The Frams I use are 99% efficient. So, let’s have some recommendations from you; be positive, informative & educational. Simply criticizing does no one any good. I’ve always made it a point not to criticize unless I’ve got a better suggestion. You..? > > I consider this to be highly unethical, and frankly a scummy thing to contemplate. The only reason you are considering renting a car is in the event of a expensive repair bill, you can (you hope) duck out of it. > If you want to experiment use your own damn equipment. If it the experiment fails and it costs you a ton of money, oh well. > Since we are not in the pit, I cannot say more. > Rick > A guys who keeps a fleet of loan cars, and would be pissed if one of my customers tried this shit on one of my cars. Well, I’m sure you’d be just as pleased when you found out something that would be to your benefit. Do you think that I’d charge to publicize it? I’ve got an idea… let me know what fleet you operate & I’ll make sure not to rent any of your vehicles. Then, when I find a beneficial answer, I’ll make sure that I offer it to the public for a fee with the note that it was to you that I’m sending a portion of their check, so would that make you feel better? Read the posts, I’m not setting out to destroy a vehicle, I can think of a 1000 ways to do that without benefiting anybody. ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 3:10am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/37 "2010-01-10T03:10:53Z")
> [@TurboNuke](#): > > Again, why are you doing this? What do you think you are gaining by adding diesel to gas? (“Doh!”) Read the thread. ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 3:18am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/38 "2010-01-10T03:18:00Z")
> [@billfish678](#): > > Dick Cheney… > > Is that you? > > Experiment on your own vehicle. No, actually, I was quoting the “leftist-liberal” line. How about we both experiment on our own vehicles? Are you up for it? No? Then just sit back & wait for someone else to do it. Got a better idea? No? Then stop complaining. I’m not here for an ethics debate, but if you’d like, I’m more well-versed than you might realize. I came here for some informative suggestions. I didn’t think it was a debate forum. But that’s OK, I’m having a good time with it! ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 4:02am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/39 "2010-01-10T04:02:25Z")
> [@ghardester](#): > > The simple answer to why adding diesel fuel to your gasoline powered engine is octane. > > In a modern gas engine the PCM (computer) adds spark during the compression stroke at the optimum time to detonate the gas. The higher the octane, the better the fuel resists pre-detonation, that is exploding before the spark is added and before the piston has completed the compression stroke. Pre-detonation or ‘knocking’ can and will damage a gas engine over time. This is why high compression engines are recomended premium gas. Adding 10% ethanol and making what is sometimes called ‘gasahol’ actually increases the octane rating. The modern vehicle has knock sensors so that the PCM can adjust the timing of the spark to use a range of fuels of different octanes. Even so, knocking can still occur by using low octane in a high compression engine. \*\*Regular gas has a RON octane rating of 91 and an AKI octane of 87. \*\* > > Pre-detonation or knock will not only damage the gas engine but it will also burn dirty since the optimum compression was not reached. So you get an underperforming engine that is burning dirty and polluting. > > Diesel engines burn fuel based upon the fuel detonating on it’s own without a timed spark being added. The low octane of diesel is part of the basis for the engine design. **The RON octane rating of diesel is 15-25.** > > All you will accomplish by adding diesel to gas or gasahol is to reduce the octane rating below what the PCM can adjust for, resulting in an engine that will chug and smoke and cause damage, if it will even run long at all. > > Wiki link about octane: > > [Octane rating - Wikipedia](http://en.wikipedia.org/wiki/Octane_rating) Sorry, didn’t quite get your first sentence… but you are indeed correct on the points you raised… just that you didn’t follow-through with all the details on the design & combustion theory. In a higher-compression gas engine, higher octane will indeed increase efficiency & mileage… for those engines requiring it. The addition of alcohol (or using it exclusively) in a high-performance application does work, but at the expense of thermodynamic efficiency. In a lower-compression gas engine, it’s just as much wasted as using 93 octane in an engine which doesn’t require it. The PCM is constantly monitoring the spark timing to fire the mixture just before knocking (detonation) occurs. This varies for a number of reasons, including the temperature, air pressure, load, RPM, & yes, the octane. As in a spark-ignited engine, the mixture is already introduced to the cylinder prior to compression, the spark must be carefully timed to coincide with the rising of the piston on the compression stroke, partially compensating for the upwards momentum of the piston while at the same time accounting for the almost instantaneous progression of the flame front through the mixture. Higher octane = slower flame progression, allowing an advance of the spark timing. Gasoline burns at a much faster rate than diesel, due in part to there already being an existing mixture present, ready & willing to explode at the first excuse. The trick is to get it to burn in a controlled fashion. In contrast, in a compression-ignition engine, the trick is to get the diesel to burn as _fast_ as possible, just the opposite of a spark-ignited engine. The rate of combustion is not controlled, nor is it needing to be controlled, as the mixture is not pre-existing in the cylinder - there is only superheated air from the 20-30:1 compression ratio. As in the spark timing, the diesel fuel injection system is timed to inject the fuel, but this occurs gradually; the flame front is similar to what it looks like inside an oil-burning furnace & the increased power is presented as a function of the lengthened time of fuel delivery, not the variation of fuel mixture pressure passing a throttle plate (= partial vacuum, lower efficiency) in a spark-ignited engine; this is, in part, why diesels are more efficient: no pumping losses. Back some years ago, Ford experimented with a concept of injecting gas similar to a diesel engine, but the volatility of gas combustion combined with the greatly-increased wear on the high-pressure injector system required (don’t forget, gasoline/gasohol is a solvent, not a lubricant) made this approach impractical & was abandoned. Back to the spark-ignited engine, the diesel does indeed have a lower _octane_ rating, but this is modulated by the knock sensor and in the minor % I’m considering, it’s just a matter of finding the optimum mixture balance of maximizing the increased BTU content of the diesel fuel vs. the reduced spark advance required from the lower octane rating. Thus, my graduated % addition of diesel to the gasohol mix… & if the diesel was going to result in a dirty exhaust, just how do compression-ignition engines get better emissions with less (or no) additional controls? Thank you for giving some thought to your response! & Yes, I’ve read the same Wiki page on octane… & fuel BTUs. Like I said previously, I’ve rebuilt everything from weedwhackers to Detroits, 2-stroke & 4, gas & diesel. I’ve had electrical engineering, chemistry, physics & electronics; still own a marine technical service business since 1991 & in that field since 1982. I’m also CDL-A rated. So, more discussion, anyone? ---
**Author:** ![The\_Central\_Scrutinizer](https://avatars.discourse-cdn.com/v4/letter/t/ed655f/32.png) [@The\_Central\_Scrutinizer](https://boards.straightdope.com/u/The_Central_Scrutinizer)\ **Post date:** [January 10, 2010, 4:24am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/40 "2010-01-10T04:24:21Z")
> [@billfish678](#): > > And Kramer on Seinfield used the write off excuse to justify stealing. With about as much believability. > > Experimenting with other people’s equipment is a shit thing to do. > > If you are SURE it won’t do damage, experiment with your own equipment and have fun. > > If you ARENT sure, keep you grubby hands off other peoples equipment. Actually, while I’m renting it, it IS mine. Trying to determine the best answer to my Question is the best way to minimize the chance of damaging _my_ vehicle, either rented or owned. Would you rather research using yours? Would you loan (rent?) me your vehicle? Would you rather me split the check from the fee I’d charge for the info between you & Rick? No? Then either provide an informative answer or just sit back & share some “whine” w/ Rick. “Thenk yew fer yer suppoert.” -Bartles & Jaymes [Previous page](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055.md?page=1) [Next page](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055.md?page=3)