Author Topic: How much is too much gasoline  (Read 1828 times)


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How much is too much gasoline
« on: August 08, 2013, 07:41:22 AM »
So, how much oil does one add to fix accidentally pumping gasoline into your diesel fuel tank?

Gasoline-waste oil blenders generally blend gasoline at 20% with waste oil, so 4x4manonbroke up-thread, who only added 3 gallons of regular unleaded gasoline to a tank of 20 gallons of diesel fuel could have added new or used oil at as much as 15 gallons to get that percentage of gasoline-to-oil to have a functional fuel blend. However, that is a lot of oil to buy new at $10-$20/gallon.

So, how little oil needs to be added to fix his mistake?

Calculations of BTU and viscosity show that a fuel blend of 50% gasoline to 50% 10-40 motor oil, with no diesel in it, has the same BTUs and viscosity of D2 diesel fuel. My gasoline-waste oil blending experiments have supported these calculations. In fact my 1983 6.2L Detroit Diesel runs like a hot rod on gasoline blended waste oils above 20% to 50%. So, I am a bit surprised that 4x4manonbroke up-thread found only 3 gallons of gasoline to 6 gallons of new motor oil, which is 33% gasoline in 17-20 gallons of diesel fuel, was not a perfectly functional fuel blend with no loss of power or performance; however, he most probably could have put half as much motor oil in and would have found his fuel blend perfectly functional.

More typically people drive up to the fuel pump when their tank is on 1/4, then fill it up, and maybe after the nozzle goes "click" they realize that they just filled their diesel fuel tank 3/4 full with gasoline. In that case, you would want to pump out the fuel tank down to about half a tank, then top off with 10-40 motor oil, or vegetable oil, which would be expensive, but cheaper than going to a garage to have them pump it out and dispose of the contaminated fuel to the tune of $300.

However there is a caveat. Since 1996 (I think) in an effort to remove toxic lead, and carcinogenic MTBF from gasoline, which were used as anti-knock additives, and octane enhancers, alcohol has been added at 10% to the fuels in the USA. Alcohol in gasoline at 10% will definitely ruin BUNA and silicone seals and hoses. Old diesel engines made before 1996 commonly used BUNA and silicone seals and hoses. Therefore, any diesel engine made before 1996 should have less gasoline in its blend.

How much gasoline is too much in a fuel blend for an old diesel engine? I do not know, but I do know that gasoline at 20% will run indefinitely on my old diesel engine. I have had some injector pump failures using blends in excess of 20% gasoline. I have not yet found out the terminal amount of gasoline in a diesel fuel blend for my injector pump. A diesel fuel blend of 50% gasoline-to-waste oil has alcohol at 5%, and that, I believe, is too much alcohol. A 25% gasoline-to-waste oil diesel fuel blend has alcohol at 2.5%. That level of alcohol seems fine.

Recent research with seal swelling tests shows that gasoline at 30% will work with BunaN and Silicone seals.
I have run various blends of waste oils and unleaded gasoline since Feb, 2007 in a 1983 Chevy G-20 van with a 6.2L diesel V-8 engine, with a Stanadyne Rotary DB2 IP. I have started the engine with no difficulty on an 80/20 (WVO/gas) blend down to 3F (-16c).  I now run 60/20/20 (WVO/diesel/gas)


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Re: How much is too much gasoline
« Reply #1 on: April 04, 2016, 06:28:34 PM »
I dont know but I thought i'd share an anecdote, that the military guys with the multifuel engines are told they can run 100% gasoline as long as they dump a couple quarts of motor oil into it.  The two issues i've heard are risk of overheating the engine (which EGT gauges should show) and lubricity failure, the motor oil at least solves one, and would have far more lubricity than diesel fuel.  Using straight up fresh motor oil should help correct it AFAIK.