# 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:** 4
**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 11, 2010, 4:05am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/61 "2010-01-11T04:05:46Z")
> [@billfish678](#): > > Let us know when you show up on Judge Judy or The People’s Court. Aahh… no problem, I keep a legal firm on retainer to handle anything which might raise its ugly head. It’s kinda nice, actually… 😃 ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 11, 2010, 4:08am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/62 "2010-01-11T04:08:13Z")
> [@The\_Central\_Scrutinizer](#): > > Aahh… no problem, I keep a legal firm on retainer to handle anything which might raise its ugly head. It’s kinda nice, actually… 😃 Are these the same lawyers that told you “you owned” a rental car when you you were RENTING it? I can just see Judge Whopner saying “I’ve heard enough, I’ve made my decision!” already. ---
**Author:** ![Rumor\_Watkins](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@Rumor\_Watkins](https://boards.straightdope.com/u/Rumor_Watkins)\ **Post date:** [January 11, 2010, 4:11am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/63 "2010-01-11T04:11:51Z")
Wapner. Please show some respect for the greatest legal luminary since Learned Hand! ---
**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 11, 2010, 4:18am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/64 "2010-01-11T04:18:39Z")
> [@billfish678](#): > > Are these the same lawyers that told you “you owned” a rental car when you you were RENTING it? > > I can just see Judge Whopner saying “I’ve heard enough, I’ve made my decision!” already. Nah, legal beagles are like toilet paper, they’re there to clean up messes. From time to time I’ve gotta give 'em something to do so they don’t get bored & get any more into creating incomprehensible laws & making sure our coffee is lukewarm… or running for office! :smack: ---
**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 11, 2010, 4:23am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/65 "2010-01-11T04:23:34Z")
> [@Rumor\_Watkins](#): > > Wapner. Please show some respect for the greatest legal luminary since Learned Hand! Hmm… Impressive! I’ll take that as a compliment! Thanks! 😃 ---
**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 11, 2010, 4:26am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/66 "2010-01-11T04:26:16Z")
> [@jasonh300](#): > > Sorry…didn’t pay much attention to it. It was all city driving and we’re talking about a vehicle that probably only gets 5 MPG anyway, so even a 20% increase (or decrease) in mileage wouldn’t have been noticeable. > > It was a full size 26’ truck with an International gasoline engine. Probably a mid to late 80s model. > > When I realized what I’d done, I stopped pumping and a friend who was with me saw a trucker filling up his semi across the station. He suggested we ask the trucker if the diesel was going to be a problem. We told the trucker what had happened and he had this amused sort of look on his face and was probably thinking that regular people should be allowed to operate large trucks. > > The trucker told us to top it off with unleaded and it might smoke a little, but we’d probably be ok. He said it wasn’t the first time he’d seen someone do the exact same thing. > > I’m also remembering that we were working with $25.00 for gas, and that topping it off wasn’t an option. Thinking that this must’ve been around 1996, gas or diesel would’ve been right around $1.00 a gallon, so we probably had 5 gallons of diesel, plus 20 gallons of regular, plus whatever was still in the tank (very little). > > The truck didn’t run any different, or produce any visible smoke. The exhaust just smelled like diesel. Thanks, I truly appreciate the constructive information! 🙂 ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 11, 2010, 5:06am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/67 "2010-01-11T05:06:00Z")
" Hence the gradual addition of diesel, & the return to a pre-problem state if any show up. " So, if you keep adding diesel fuel till you burn something up, ruin the sensors, or break something, you can magically return to the “pre-problem” state by runing lower concentration/diesel free fuel through the engine? I did not know that. ---
**Author:** ![thirdname](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@thirdname](https://boards.straightdope.com/u/thirdname)\ **Post date:** [January 11, 2010, 7:02am UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/68 "2010-01-11T07:02:22Z")
> [@The\_Central\_Scrutinizer](#): > > Yeah, that’s the standard tire-store & auto manuf. mantra. Yet I’ve never encountered it, & I’ve read much info to the contrary. The info I mentioned is correct. In all the years of driving, I’ve never had a set of tires worn in the middle before they were worn along the outside edge, & once I increased the pressure to the rated maximum, all was as I’d said. Roughly 1/3-1/2 way through the tires life, I have them dismounted, switched so that the opposite side now faces out (the direction of rotation remaining the same) & get more than the rated mileage life out of the tire. This is only applicable for symmetrical tread designs. I also spray marine-grade silicone inside & out to minimize ozone damage & help seal the tires micropores from seeping pressure gradually over the months. That saves fuel as well as tires. Have you performed tests of your car’s stopping distance at these higher pressures, on a variety of surfaces? Considering how much money is put into making cars more fuel efficient, if it was that easy and there were no downsides you have to wonder why every car company doesn’t recommend 45 psi so they can get better EPA ratings. Isn’t silicone slippery? Is that a good thing to have on tires? Are you spraying it on the tread, or just the sidewall? ---
**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 11, 2010, 7:15pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/69 "2010-01-11T19:15:14Z")
> [@billfish678](#): > > " Hence the gradual addition of diesel, & the return to a pre-problem state if any show up. " > > So, if you keep adding diesel fuel till you burn something up, ruin the sensors, or break something, you can magically return to the “pre-problem” state by runing lower concentration/diesel free fuel through the engine? > > I did not know that. Well, you’re taking me out of context & jumping to conclusions, so with the exception of “burning something up”, “ruin the sensors” or “break something”, yep, that’s about the size of it. Just like getting a splash-blended load of methanol fuel from a cheap gas station, or having to purchase high-priced system cleaners/decarbonizers to remove the damage from all the alcohol in the fuel. I wonder just how “Marvel Mystery Oil” has gotten along so well for so many years? Or any other oil-based additive, of just about all which contain "petroleum distillates = kerosene? ☹ ---
**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 11, 2010, 7:21pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/70 "2010-01-11T19:21:12Z")
> [@thirdname](#): > > Have you performed tests of your car’s stopping distance at these higher pressures, on a variety of surfaces? Considering how much money is put into making cars more fuel efficient, if it was that easy and there were no downsides you have to wonder why every car company doesn’t recommend 45 psi so they can get better EPA ratings. > > Isn’t silicone slippery? Is that a good thing to have on tires? Are you spraying it on the tread, or just the sidewall? I’d think, after driving nearly everything from 2 to 18 wheels for almost 35 years, I’d have a good enough idea as to how my vehicles handle both before & after… have you considered that the larger contact patch also hydroplanes easier? That narrower tires perform better on wet roads vs. wider ones do better on dry? That stiffer sidewalls & firmer pressures resist rolling over under hard/sudden cornering? That the auto manufacturers rather their vehicles ride nice & soft like driving on marshmallows because that’s what American drivers have become used to, vehicles that handle like drunken hippos on ice skates? Go figure! :smack: PS - Think about the silicone: they used to offer it in a spray can called “Instant Snow Tire” because it released the snow from the treads, that any that got onto the treads themselves almost immediately got worn off by contact w/ dry pavement… SHEESH! What a “maroon”! ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 11, 2010, 7:26pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/71 "2010-01-11T19:26:31Z")
> [@The\_Central\_Scrutinizer](#): > > Well, you’re taking me out of context & jumping to conclusions, so with the exception of “burning something up”, “ruin the sensors” or “break something”, yep, that’s about the size of it. > ( So, if something bad and unexpected doesnt happen, then something bad and unexpected won’t have happened? If you are so DAMN sure it aint gonna hurt a car, why the hell dont you just use your own damn car? ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [January 11, 2010, 8:10pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/72 "2010-01-11T20:10:44Z")
> [@billfish678](#): > > So, if something bad and unexpected doesnt happen, then something bad and unexpected won’t have happened? > > If you are so DAMN sure it aint gonna hurt a car, why the hell dont you just use your own damn car? Yup the only reason to use someone else’s car is because of the potential for damage. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [January 11, 2010, 8:35pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/73 "2010-01-11T20:35:50Z")
> [@The\_Central\_Scrutinizer](#): > > 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. Are those Imperial (UK) gallons? That would translate into 60 city/63 highway for US gallons. You general point still holds, but not quite as dramatically. ---
**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 12, 2010, 3:48pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/74 "2010-01-12T15:48:52Z")
> [@billfish678](#): > > So, if something bad and unexpected doesnt happen, then something bad and unexpected won’t have happened? > > Umm… Yes, isn’t that about what I said? Whoa, Duude, could I try a coupla of whatever it is that you’re takin’? 😕 > If you are so DAMN sure it aint gonna hurt a car, why the hell dont you just use your own damn car? 'Cuz I’m sure that you won’t let me use YOURS! 😃 ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [January 12, 2010, 3:51pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/75 "2010-01-12T15:51:31Z")
> [@The\_Central\_Scrutinizer](#): > > 'Cuz I’m sure that you won’t let me use YOURS! 😃 Cause I got enough technical sense to NOT let you do it. Why don’t you mossey over to the BBQ pit part of the forum and see what people really think about this whole rental car plan? ---
**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 12, 2010, 3:52pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/76 "2010-01-12T15:52:38Z")
> [@pulykamell](#): > > Are those Imperial (UK) gallons? That would translate into 60 city/63 highway for US gallons. You general point still holds, but not quite as dramatically. Hey, check out the info on Wiki, search for “Toyota Prius”. I’m sure that was in Imp. gals, which are roughly 10% more (I think). I also recall that the equiv. was mentioned for U.S. mileage, but their fuels source is most probably different as well. Wonderful site, Wiki… Thanks! ---
**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 12, 2010, 3:57pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/77 "2010-01-12T15:57:47Z")
> [@billfish678](#): > > Cause I got enough technical sense to NOT let you do it. Why don’t you mossey over to the BBQ pit part of the forum and see what people really think about this whole rental car plan? Thank you for recommending it, bit I’ve got a world of things to accomplish, & like I said before, I didn’t come here for a debate or to ask permission or group approval of the masses. I WORK for a living. Although when I get old, feeble, bored & suffering w/ Alzheimer’s, perhaps I’ll amuse myself there. Perhaps I was misdirected to this page when I came asking a Question; thanks for letting me know that the “pit” is for hen-pecking & debates. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [January 12, 2010, 4:19pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/78 "2010-01-12T16:19:51Z")
> [@The\_Central\_Scrutinizer](#): > > Hey, check out the info on Wiki, search for “Toyota Prius”. I’m sure that was in Imp. gals, which are roughly 10% more (I think). I also recall that the equiv. was mentioned for U.S. mileage, but their fuels source is most probably different as well. So the [Wikipedia page on the Prius](http://en.wikipedia.org/wiki/Toyota_Prius) gives a combined US fuel economy of 50mpg for the 2010 Prius, and a combined UK fuel economy of 54.7mpg (both in US units). That’s surprisingly close, considering they likely use different driving cycles. As for what started this discussion, the EPA estimated mileage for the Prius indeed used to be higher, but in 2007 the testing methodology was changed to reflect what were felt to be more realistic driving conditions ([Wired article cited](http://www.wired.com/cars/futuretransport/news/2007/05/hybrid_mpg) on Wiki). Nothing to do with E10, if that was the implication. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [January 12, 2010, 5:14pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/79 "2010-01-12T17:14:08Z")
> [@The\_Central\_Scrutinizer](#): > > C > 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! I have enjoyed this thread, but stayed away mainly because of the line quoted above about marine engines being simpler and tougher than today’s auto engines. What specifically is ‘simpler’? Since marine engines range from multi-port injected 502 cubic inch Mercruisers built from GM big blocks to sophisticated Honda 4-stroke V6 outboards based on the car maker’s auto line, what exactly makes marine engine simpler? Marine engines are engines with some parts replaced for marine use (such as non-sparking components, brass plugs or other add-ons that can withstand salt/water/etc. These parts are mostly accessories. The internal and fuel delivery systems on marine engines (filters aside) don’t like water. Keeping water out of a marine engine is just as important as on a car engine. Marine engine internals don’t stand up to water any better than car engines. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [January 12, 2010, 6:50pm UTC](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055/80 "2010-01-12T18:50:25Z")
> [@ghardester](#): > > \*\*Regular gas has a RON octane rating of 91 and an AKI octane of 87. \*\* > […] > 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.** So in a couple years, when _my_ kid calls and tells me he accidentally put about 1.5 gallons of diesel in the tank, I’d be better off having him top it up with premium than regular? Or maybe buy some bottles of octane booster and add some of that? (They sell that, don’t they?) [Previous page](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055.md?page=3) [Next page](https://boards.straightdope.com/t/adding-diesel-fuel-to-gasohol-to-increase-mileage-efficiency/524055.md?page=5)