Adding diesel fuel to gasohol to increase mileage/efficiency?

Factual Questions
1

Considering that the 2 main ideas behind “gasohol” (E10 & E85) have been to 1. Decrease our dependence on foreign oil & 2. Decrease tailpipe emissions, 2 other negative effects have certainly been noted (by me, at least!). 1. The net cost has gone up, both at the pump & in reduced mileage/efficiency & 2. While the internal combustion has gotten more efficient, the resultant elemental carbon has been left to accumulate inside the engine, notably in critical & expensive areas, requiring either regular additions of chemical treatments on up to costly mechanical services to remove.

My Question, which I’ve not found asked & answered anywhere I’ve looked on the 'net, is at what percentage might one be able to add diesel (taxed road or untaxed offroad) to existing gasohol fuel supplies to be able to recover or even improve the mileage efficiency before any deleterious effects on either the mechanical parts of the engine itself or the fuel system or sometimes quirky & sensitive emissions equipment of the vehicle? Diesel has a notably higher BTU content per gallon & is a lubricant as well. The ULSD requirement today should minimize any damage from any sulfur compounds in the delivery, management, combustion & expulsion from the vehicle.

For instance, we have a 2004 Toyota Prius. When we first bought it, the advertised mileage was 60 city/50 highway. We did better than that consistently by both being careful drivers & applying a few simple tricks not everyone knows. Today, now that E10 has been mandated & is being consistently supplied in our area, our mileage has dropped to somewhere between 40-45. Even other Prius owners have mentioned the reduced mileage as well & that has been reflected in their advertised posted EPA estimates.

Our major concern is that the Prius is not only a rolling mass of processors, it also has an elastomeric bladder in the tank which (reportedly) precludes our running it on 100% alcohol (which would at least be better for the engine than the current gasohol!) More than one person has mentioned that it might not pass emissions tests w/ diesel mixed in the fuel, but at least here in DE they can’t do the tailpipe test on the Prius - the engine shuts off & switches over to electric when in park or when not under load. The only test done is to connect a multiplug under the dash to check for stored trouble codes.

Without risking my (now classic) 1995 Saturn SL2 or Prius, my only other real-world test idea has been to rent a similar car, fill the tank w/ standard fuel, & drive it using a gallon of fuel at a time, adding a gallon of diesel fuel to replace it, gradually increasing the percentage of diesel until it starts to complain w/ hiccups and/or lights on the dash.

I’ve worked over 27 years in the marine technical service industry & own a business in that field since 1991, so am well acquainted w/ the problems that adding alcohol to either gasoline alone, or especially to a gas/oil mix, can cause to marine engines, which are generally tougher & simpler than today’s auto engines. Any water contamination is catastrophic…

So, any answers available here? Thanks!

2

Mileage on the 2004 Prius was rated at 45 City and 48 Highway.

I’ve never heard of any Toyota, including the hybrids, that get better than 50 MPG.

3

Doesn’t diesel fuel gel in cold temperatures? I’m not sure how that is managed in a diesel engine, but in a gasoline engine not designed for it I would think it would raise hell.

4

I would think that diesel add to gasoline would lower the octane rating. Possably causing problems.

5

That’s what I was going to say. Mis-fueling is an issue to watch for in aircraft. Put jet fuel in a piston engine, and you lose power. Put avgas into a jet engine, and you risk burning it up.

6

Actually, NOT. We were there, Toyota did indeed advertise 50 highway/60 city MPG, both on the EPA sticker & on broadcast & printed ads. We bought the 2004 Prius new. In fact, we still have the original sticker. We typically got 55-60+ MPG in mixed driving (in a largely rural area) & even higher on a long constant cruise. At times, we got 70-72 MPG on the 10-12 mile trip back from the fuel station, but this was with an already warm engine & on a highway, the last third in town @ 25 MPH (on purely electric power = no fuel use at all). At speeds less than 40 MPH on a level road, it will run on electric alone for a good number of miles, especially when you’ve got the AC/heat turned off. When at highway speeds, to minimize wind resistance, we keep the windows closed whenever possible. It’s actually more fuel efficient to use the environmental system instead. We’ve got a very accurate knowledge of the fuel usage; the LCD MFD gives us both tank average, real-time & a bar-graph over a 30 min. time to monitor fuel usage. We can even see the effects of AC/heating system usage & it gives us an active graphic diagram of the engine, motor, battery & the energy flow, including that reclaimed on the regenerative braking system.

The EPA rating was continued for a period of time until the complaints started coming in once the E10 was mandated a year or 2 afterward. Now, the common rating is about what you mentioned. Now, the newest version for 2010, w/ the Atkinson-cycle engine, is rated EPA combined 50MPG. For the UK, their rating is 72 city/76 highway. Of course, their testing & fuel composition might be different, but you get the picture.

The few simple tricks I mentioned are:

  1. Using quality tires (we like the Goodyear TripleTread Assurance) & Pump them to their rated maximum for improved mileage, handling, even tread wear, cooler operating temperature, longer life &, of course, better mileage.

  2. Using quality synthetic oil (we recommend Mobil 1) @ 0W-30 (for this particular vehicle) as this has the lowest pumping friction, full protection @ operating temperature, exceptional thermal stability & resistance to chemical breakdown (sludging). In my 1995 Saturn SL2, I’ve used 10,000 mile oil changes w/ no problems & it’s got close to 150,000 miles on it, still runs like a bat outta hell, averaging 30 MPG, up to 40 MPG on a highway cruise. My 34’ motorhome has a 1993 GM HD 7.4L (454CID) w/ dual-injector throttle-body. I typically get ~10 MPG w/ it, using Mobil 1 10W-30 & TufOil; on a trip from SE DE to NW PA & back, through all the mountains it didn’t burn a drop, & I was towing the Saturn. The GM 454s are known oil-burners… the on-board 5KW Kohler generator has gone far beyond it’s recommended 2000hr rebuild point & still runs like a top. We use Mobil 1 15W-50 & TufOil in it, burns next to no oil (it is, after all, air-cooled & runs hot) & we only change the oil when it gets blackish. Provided your vehicle doesn’t burn oil, use the lowest viscosity possible for ease of cold cranking & low friction & the recommended high-temperature viscosity for engine protection. We also use Mobil 1 synthetic automatic transmission fluid, or in a manual gearbox, Mobil 1’s synthetic gearlube.

  3. 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!)

  4. We keep the car clean & waxed (we use Mother’s Carnauba). This also reduces air resistance. Besides, we like our vehicles & lookin’ good is feelin’ good!

  5. Since the Prius’ air conditioning system is electric, it costs much less to run than conventional automobiles, but the heating system is a different matter. We keep the heat to a minimum as there are times the engine has to come on solely to produce heat alone, where otherwise it wouldn’t, the main battery already being charged. This reduces the mileage in cold weather, in contrast w/ conventional autos, which have waste heat available at all times anyway.

  6. We opted for the H.I.D. headlights, being brighter & more efficient than conventional lights, & have used LED lights wherever we can, since they use less energy than filament bulbs (plus last practically forever).

  7. We use Rain-X on all the windows, since using the wipers takes energy & increases drag when in operation. In most driving conditions, Rain-X type products actually increase visibility the harder it rains, especially on windows which don’t have wipers.

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.

So, there’s my “STR8 Dope”. I’ll be reading all the additional responses to my original Question, thanking each one for taking their time to provide their input.

7

Diesel #2 will gel in common cold temperatures, somewhere around freezing (don’t recall the specifics @ this point); this is why Diesel #1 is either blended or used itself according to the local climate conditions. Diesel #2 is generally cheaper & gives better mileage & injector lubrication. Diesel fuel, either #2 or #1, when added as a minor component to a gasoline/gasohol fuel, should encounter no gelling until it gets close to gasoline’s own gel point, somewhere approaching 60 degrees below zero F. I’ve seen gasoline gel! Gelling is actually the wax content coming out of solution & blocking the fuel delivery system. In interstate trucking, picking up fuel in one location, then say, driving north through a cold front several hundred miles away, shutting down in a stop due to freezing roads, then being unable to start due to gelled fuel is a real problem. I know, I’ve driven interstate rigs. Diesel trucks have fuel heaters, either electric or run off the engine cooling system, but neither run while the engine is shut down. Adding an anti-gel is always a good idea when traveling in questionable conditions.

8

I don’t know this for sure… again, since the percentage added would be relatively minor, I don’t see that it would be much of an issue. Also, most modern gasoline engines have sophisticated management systems that monitor & automatically compensate for any variations in octane or pinging conditions. An example, although many higher-performance vehicles state the requirement for higher-octane fuel, they will run (although with less power) on lower-octane fuel by modifying the fuel mixture, timing & other parameters. Similarly, fuel injection doesn’t have to be re-calibrated for different altitudes, unlike carbureted engines.

Since diesel fuel has a much higher carbon content, a larger molecule, I’d think that under spark-ignition conditions, it should actually slow the combustion rate, which in addition to providing more heat to the process, would also prolong the peak combustion pressures farther down the piston stroke, increasing efficiency, similar to what higher-octane gasoline does. It would be my thought that the injectors would also be lubricated in the process.

The high octane rating of alcohol fuel is due to its lower BTU value & cooler burning temperature. It has a much lower carbon content, & the combustion of hydrogen & oxygen doesn’t produce that much heat in relation to the combustion of carbon & oxygen (2 hydrogen : 1 oxygen = water; 1 carbon : 2 oxygen = carbon dioxide).

9

I have experience with this. My daughter called home one day, she had accidently put about 1.5 gallons of diesel in her Honda minivan. I told her to fill the car with regular to dilute the diesel to see what happens, the car might run just fine. It didn’t. She drove only a few miles before the car started running like crap. It quit running after 8 miles.

She had it towed to the dealer and it cost her $420, they had to replace the gummed up fuel pump and clean all the fuel injectors. Plus 15 gallons of fuel had to be disposed of.

Don’t add diesel to your car unless you are willing to accept the consequences.

10

To my knowledge, jet fuel is basically highly-refined kerosene. Higher BTU, not as explosively volatile as gasoline, but lighter than diesel #1. I was told that using kerosene in a gasoline engine (not as a blend) would destroy the commonly cast-aluminum pistons. It might be a matter of too lean a mixture (mis-jetting). Supposedly, using iron pistons would solve the problem, but as one of the factors defining a reciprocating engine’s power output is its RPMs, that would be limited by the mass of the reciprocating parts; namely, iron is a lot heavier than aluminum. Whether or not adding kerosene to gasoline/gasohol in today’s electronically-managed fuel injection engines seems moot when considering that kerosene’s relative high cost per BTU hasn’t seemed worth pursuing.

Putting gas, aviation or otherwise, into a jet engine would do a lot more than burning it up… have a remote starter, stand back & get out the hot dogs & marshmallows! :eek:

11

Unless she used a funnel, that should be impossible as the diesel nozzles are fat, like the old leaded gas nozzles, and won’t fit into a car’s filler neck.

Or did she do something weird like run out of gas, hike to a gas station to buy or borrow a gas can, and filled that with diesel by mistake?

12

Since I can only guess at the fuel tank capacity of that minivan as somewhere ~15 gallons, it seems that in this instance that % mixture might be too much. Also, it might have had to do with how well it was mixed - if the engine got a slug of relatively unmixed diesel, that surely would shut it down.

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. Since most common fuel system cleaners are kerosene-based, it might very well have been that your daughter’s fuel system already had some sludge, etc. in the tank & adding the diesel just stirred it up & got it into the fuel system. Also, while gasohol will tolerate a certain amount of water contamination, the addition of diesel to the mix will result in the diesel falling right out of solution. At least in the marine industry, it’s known as “phase separation” & was a real problem in the days of pre-mixed 2-stroke fuel. When alcohol was introduced into the gasoline supply, it would pick up the water contamination & mix it into the gas but the oil in the mix wouldn’t tolerate the disparity in specific gravities & would come out of solution, rising to the top of the tank, leaving the gas-alcohol-water mix on the bottom, resulting in an engine needing lubrication suddenly having the oil removed under usually high load, turning it into an expensive anchor with no notice.

Chemically, both kerosene & diesel are a lot less aggressive than either gasoline or alcohol, so the chance of actual damage from those fuels directly to fuel system parts is remote. The one exception to this has been with galvanized steel tanks; the trace of sulfur in diesel fuel (today much less than in the past) would dissolve the zinc & leave the compound in the injectors, requiring changing the fuel tanks to either stainless steel (preferred) or HDPE or aluminum.

I’m fairly knowledgeable in both chemistry (my Dad taught it @ the U.S.N.A. & I got it full measure from him & years of chemistry myself) plus many years of servicing all kinds of marine engines, both 2-stroke & 4, gasoline & diesel. Kerosene (& diesel, to a lesser degree) will dissolve & clean sludge & varnishes, etc. that neither gasoline or alcohol will touch. In fact, bio-diesel is even more detergent - when switching to its use in marine vessels, I always advise taking along an extra case of fuel filters until the tanks are thoroughly cleaned or the engines will most probably be shut down by all the sludge brought up from the bottom of the tanks.

I’d be interested in hearing more in detail about your daughter’s experience as well as any others. Thanks!

13

It’s possible. On another board there is a person that works at a gas station and has reported a number times when somebody filled up with diesel at the pump. No special equipment is needed.

14

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.

15

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.

16

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.

17

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.

Does the cost savings of not using the wipers offset the cost of Rain-X? I doubt it.

Yes, but you are making the oil pump work harder. Also big filters make the oil pressure fluctuate more.

18

Used to put a gallon of kerosene in a 30 gal tank to prevent vapor lock when pulling heavy loads in the 70’s… Works good… No fancy injection or electronics then.

Why does saving the environment always make it more costly and complicated for man?

Oh, burned 100LL av gas in a 76 Chrysler Cordoba with no problem …

Need to up your octane, just add Toluene from the paint store.

YMMV

19

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.

20

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.