Help - diesel fuel in gas engine

[65Matt]

My coworker accidently put diesel in a gas engine. (long story) The truck is currently running rough.

How bad will this damage the engine? Can we just dilute whats in the tank with cheap gas, or should we take the diesel out?

[Monroe]

I'd drain it or siphon out as much as possible and then fill with fresh regular.

Monroe

[SalKhan]

Don't plugs get fouled pretty quickly?

[Elliswon]

It's not your truck, tell your buddy to go ahead and run it on diesel and report back to us on what happens.

Seriously, if it were mine, I wouldn't run it until it was drained and flushed with the proper fuel. Seems like the safer alternative.

[ROUSHGTR]

Originally posted by 65Matt
My coworker accidently put diesel in a gas engine. (long story) The truck is currently running rough.

He should be thankful that he didn't put gasoline in a diesel engine...

Drain it out and it should be fine.

Jim

[Trumps]

I thought diesel pumps had larger diameter snouts to avoid this kind of mistake?

[jfranci3]

Originally posted by ROUSHGTR

He should be thankful that he didn't put gasoline in a diesel engine...

Drain it out and it should be fine.

Jim

I don't know if anyone watches the show "the Amazing Race", but someone people did that in that show. The engine ended up just running rough and dying. They drained the gas and added diesel. The trucks fired right up after that.

[Tim]

not to bad adding gas to diesel system. oil burners can tolerate some "foreign" material. but the gas engine will most likely not run well. I saw a guy do this many years ago and he made it out of the station and onto the road followed by a 2 story white smoke cloud. not going to burn well hopefully it will just foul the plugs. drain it and add some gas to flush and fill with new gas.

[onestep]

From what I have been told the newer diesels will not tolerate gas. They rely on the lubricating ability of diesel fuel to keep the injectors, and high pressure pumps from destroying themselves.

[Tom351]

Originally posted by Trumps
I thought diesel pumps had larger diameter snouts to avoid this kind of mistake?

It must be an older truck. I could drop a golf ball down the gas snout in my 1967 Mustang.

[jetenginedoctor]

Diesel in a gas engine will cause serious damage. The entire fuel system needs to be drained and flushed. Don't try to run the vehicle until this is done.

BK

[Rupert]

What kind of damage? I expirimented with a 1:3 diesel/gas mix in the fairmont for a while, the only problems I had were with the fuel filter plugging up. I think if it were warmer out when I had done this things would have turned out even better.

ahh, nothing like diesel fumes from a gas burners tailpipe...

[Helmetcase]

Isn't the Octane rating of diesel somewhere in the 40s? Its pretty much like trying to run it on really thin oil, isn't it?

As in KA-boom bye bye head gaskets, internals, and everything else. I'm sure that gunky diesel isn't so hot for the fuel delivery system either.

[Judd]

Putting diesel in a gas motor will just irritate you, no permanent damage done. Cats and the O2 sensors may not like it much though. Putting gas in a diesel will end up in a bad day if enough gas is added. A diesel will run on just the fumes from a rag soaked in gas when it is held near the intake. It's actually a good little trick when bleeding air from the fuel lines in a diesel.
Reminds me of something my friend did once. We went to get some kerosene for the shop heater one day and we were yappin about something. Well, he was so busy yappin that he forgot why he pulled up to the kerosene pump. He stood there pumping kerosene into his fuel tank. I never said a word. He topped off his tank, went in the store and paid for his fuel. Still, I didn't say a word. He started the truck, pulled out and started to return to the shop. Got about a mile or so and the truck started running rough, smokeing pure white smoke. It was bad, looked like a mosquito sprayer! The thing would only run at idle/part throttle. He figured it out pretty quickly once I started laughing. Funny as heck!

[jetenginedoctor]

Okay, couple things to consider.

First of all, diesel engines are compression ignition engines. The heat of compression is all it takes to ignite the air/fuel mixture in the combustion chamber. This is due in part to the very low octane/anti-knock index of the diesel fuel. So, putting diesel into a gas engine creates a very low-compression diesel engine.

Next, consider the much higher BTU content of diesel fuel. I can't quote from memory the numbers of typical diesel fuel and unleaded gasoline, but if somebody is bored, you can probably find it on the internet and see what I mean. That higher BTU coupled with the richer air/fuel ratio of a gasoline engine means you're throwing a lot of diesel (comparitively) into that combustion chamber. If there's enough gasoline there to help ignite the diesel, the added BTUs (heat) can damage pistons, overheat/warp heads, not to mention the damage to rod and main bearings caused by the pre-ignition garanteed by the resultant ultra-low octane value of the diesel or diesel/gasoline mixture.

It's so serious a problem, in fact, that if you accidentally burn Jet-A fuel in a gasoline reciprocating aircraft engine, you must OVERHAUL the engine. If I remember correctly, it's in a Service Bulletin. . . . mandated by the FAA.

Its okay I guess if you want to burn diesel in a gas engine. No skin off my ass, but don't say you weren't warned with the pistons fall apart or you hammer your bearings into razor blades.

BK

[blown84gt]

Well, I can speak from experience here. My wife loaded her 91 GT with diesel at a BP station 65 miles from home. She made it a half mile or so when it stopped on her. When I got there and checked the usual things, I knew I smelled diesel fuel, but I thought no way she did that. It would run until you put it in gear (automatic). I got her going by holding the rpm up and throwing it in gear. Once on the interstate, I left it in third, no overdrive. I made it home fine. Next day, I smelled the diesel again, so i topped it off with gas and she immediately ran better. Next tank, all is well. I was prepared to replace o2 sensors, cats, etc. but I assume no serious damage was done since this happened 6 years and 65k miles ago..........

[Keith Shaw]

BK, I think you're talking about some pretty extreme situations in your examples- none of that is likely to happen to a gasoline engine operated at part throttle that has had some diesel fuel added to it.

First of all, diesel engines are compression ignition engines. The heat of compression is all it takes to ignite the air/fuel mixture in the combustion chamber. This is due in part to the very low octane/anti-knock index of the diesel fuel. So, putting diesel into a gas engine creates a very low-compression diesel engine.

I don't agree with that assessment- the heat of compression is only one aspect of the diesel's diffusion combustion process. Factors such as bowl shape and piston shape, high compression ratio, direct injection timing and spray pattern- all these play a role in creating the diffusion driven combustion process that is the trademark of the diesel engine. What you really get when you add some amount of diesel fuel to a gasoline engine is a poorly running gasoline engine that acts like it's burning a lot of oil. The nature of combustion in the engine has not changed.

Next, consider the much higher BTU content of diesel fuel. I can't quote from memory the numbers of typical diesel fuel and unleaded gasoline, but if somebody is bored, you can probably find it on the internet and see what I mean.

No need for boredom; I have tons of fuels analyses laying around. This may surprise you, BK, but in terms of mass the net heating values for diesel and gasoline are very similar. Both are right around 18,450 BTU/lb. Diesel is somewhat denser, however, so on a volume basis the diesel will come out roughly 8-11% higher in total energy. Certainly nothing that would cause mechanical failures in normal operation of a gasoline engine.

It's so serious a problem, in fact, that if you accidentally burn Jet-A fuel in a gasoline reciprocating aircraft engine, you must OVERHAUL the engine. If I remember correctly, it's in a Service Bulletin. . . . mandated by the FAA.

These gasoline engines are operated at rated power for takeoff and are pretty heavily loaded even during cruise. Most aviation engines are also high compression engines that require leaded fuel (either 100LL or the older 100/130 AvGas). With a high octane requirement and highly loaded operation, fueling these engines on something akin to diesel (such as Jet-A) would be a recipe for disaster. Bear in mind that this doesn't really translate to the light-duty operation of a passenger car's gasoline engine. The amount of power required to keep a Honda Accord at 50 mph on level ground is roughly 8 hp. Even normal accelerations don't present a very significant load to the engine in most light duty vehicles.

Its okay I guess if you want to burn diesel in a gas engine. No skin off my ass, but don't say you weren't warned with the pistons fall apart or you hammer your bearings into razor blades.

Again, I don't think thats very likely to happen. You'd really have to work at it. For anyone who has accidentally added diesel to their gasoline vehicle, simply siphon out what you can from the tank, then fill it back up with gasoline. Any diesel left in the fuel system won't present a problem IMO.

[jetenginedoctor]

BK, I think you're talking about some pretty extreme situations in your examples- none of that is likely to happen to a gasoline engine operated at part throttle that has had some diesel fuel added to it.

Who’s talking about part throttle? Most people who erroneously fill their gas tank with diesel are puzzled why the vehicle runs badly, and go ahead and give it whatever throttle they need to in order to get down the road. Again, we’re talking about MOST people, not folks who have some understanding of the fact that diesel doesn’t go in the fuel tank of gasoline powered vehicles, and why. They keep booting it in the ass and cursing the gas station for selling them “bad gas.” They keep pushing it however hard they must in order to drive whatever speed and accelerate at whatever rate they’re accustomed to, all the while still oblivious to the fact that their indeed damaging their engine.

I don't agree with that assessment- the heat of compression is only one aspect of the diesel's diffusion combustion process.

Keith, I know this. I’m not saying that all it takes to make a diesel engine is to fuel your station wagon next to the big rigs at the nearest truck stop. I’m stating that it is the heat of compression that makes a diesel engine work, thus the term compression ignition engine.

Factors such as bowl shape and piston shape, high compression ratio, direct injection timing and spray pattern- all these play a role in creating the diffusion driven combustion process that is the trademark of the diesel engine.

Agreed. The above factors are what are necessary for a properly designed/executed diesel engine. But considering the added heat the diesel fuel creates within the combustion chamber, I’d say it’s safe to bet that there is at least one unintentional source of ignition in the ground electrode of the spark plug, and likely just enough heat of compression to facilitate auto-ignition. After all, I don’t think that direct injection, combustion chamber shape and spray pattern technology were existent when Mr. Diesel invented his compression combustion engine, yet he still managed to make them run. . . right?

What you really get when you add some amount of diesel fuel to a gasoline engine is a poorly running gasoline engine that acts like it's burning a lot of oil. The nature of combustion in the engine has not changed.

But what’s not defined is how much diesel was added. One would figure that if they’re putting fuel in a tank, its because there was probably very little fuel in there. Who buys fuel with 7/8 showing on the gauge? Granted, this is an assumption, but bear with me.

If you’ve got ‘a little’ gas in the tank, then top it off with diesel, you’ve effectively got a tank full of diesel. That little bit of gasoline has little bearing on the burn characteristics of the diesel fuel that has now absorbed it. Keep in mind, it doesn’t take much oil leaking past rings or valve guides to cause detonation/pre-ignition. Well now you’re introducing ‘oil’ into the combustion process in vastly greater proportions than your leaky rings or valve guides could ever dream of. Surely you can see where this is a bad thing.

This may surprise you, BK, but in terms of mass the net heating values for diesel and gasoline are very similar. Both are right around 18,450 BTU/lb.

In mass, yes. In volume, no.

Diesel is somewhat denser, however, so on a volume basis the diesel will come out roughly 8-11% higher in total energy. Certainly nothing that would cause mechanical failures in normal operation of a gasoline engine.

Since fuel injection systems operate by injecting a ‘known’ volume, of fuel (not mass) into a ‘known’ volume of air, the added BTU value of diesel would be of significance. If it had the same anti-knock characteristics of gasoline, this added heat energy would be beneficial. However, because of the unpredictable nature of an unknown and uncontrolled mixture of gasoline and diesel fuel, uncontrolled combustion and engine damage are the results.

These gasoline engines (aircraft) are operated at rated power for takeoff and are pretty heavily loaded even during cruise.

This is true. Still, if memory serves, the SB states that an engine run for any time at any power setting with any measurable quantity of turbine fuel must be overhauled. Again, this is from memory, and I’ll dig through boxes of college notes and SBs if you insist on proof. In my opinion, if it’s a big enough deal that the FAA says you have to disassemble and inspect any certified gasoline burning engine that’s run for any amount of time on fuel contaminated by turbine fuel, then I think it’s a big enough deal that folks should not be advised that it’s ‘okay’ to burn through a tank of it in their car. (pardon the run-on sentence.)

Most aviation engines are also high compression engines that require leaded fuel (either 100LL or the older 100/130 AvGas). With a high octane requirement and highly loaded operation, fueling these engines on something akin to diesel (such as Jet-A) would be a recipe for disaster.

Wrong, wrong, WRONG!!!!! Most general aviation gasoline engines have a static compression ratio of around 8:1. These engines were designed to run on rather low-octane fuel, something to the order of 80 octane. Only a very small percentage of general aviation engines require octane ratings of 100 or more. These are some of the high-performance turbocharged and/or supercharged engines found on select high performance aircraft. Your typical non-turbo Cessna owner has probably done the STC (supplemental type certificate) that allows him or her to fuel their aircraft with 87 octane motor fuel. Why? Because it costs about half as much, you can buy it 24/7 in most places, and it has negligible negative effects on engine performance, operation, or longevity.

Bear in mind that this doesn't really translate to the light-duty operation of a passenger car's gasoline engine. The amount of power required to keep a Honda Accord at 50 mph on level ground is roughly 8 hp. Even normal accelerations don't present a very significant load to the engine in most light duty vehicles.

Again, I don’t think you’re using a very realistic scenario. How safe is it to assume that this was a Honda Accord being driven on level ground at 50 MPH? Who drives 50 MPH? How likely is it that the ground was level? Normal accelerations are likely to require roughly half of the engine’s available horsepower in order to bring the vehicle to cruising speed in a reasonable length of time.

Factor in that the engine will NOT be operating properly, will NOT be efficiently converting heat energy into kinetic energy, and the fact that it doesn’t take long for the sound of the under-hood death rattle to do really ugly things to an engine. I mean really, I’m not expecting a worst-case scenario, just a real-world realistic scenario.

For anyone who has accidentally added diesel to their gasoline vehicle, simply siphon out what you can from the tank, then fill it back up with gasoline. Any diesel left in the fuel system won't present a problem IMO.

I agree. What you’re saying here is pretty much the same thing I said in the first place. My intention was not to create a flame war or argument. Rather, I wished to stress that it’s a bad idea to just shrug your shoulders, tolerate the vehicle overheating and running like shit till you burn through a tank of diesel, then just top off again with gas and pretend it never happened. I think the time and trouble you might go through to drain the tank and fuel system is well worth the damage you’ll avoid. Like I said, run the hell out of it on diesel, it’s no hair off my ass. Just trying to offer warning, that’s all.

YMMV

BK

On edit--replace my use of Service Bulletins with Airworthyness Directives. Brain fart. . . it happens.

bk

[jetenginedoctor]

An excerpt from FAA Airworthyness Directive #96-02-04

On June 23, 1994, the Federal Aviation Administration (FAA) issued priority letter airworthiness directive (AD) 94-14-11, applicable to Franklin Model 6A4-150-B3 and 6A4-165-B3 reciprocating engines, installed on the following U.S. registered aircraft: N6209M, N74231, and N752C. That action requires teardown and analytical inspection for engines certified to operate on 91 or higher octane aviation gasoline (avgas), and differential compression test and examination of the oil filter for engines certified to operate on 80 octane avgas. That action was prompted by reports of reports of aviation gasoline (avgas) being contaminated by Jet A fuel. After investigation, the source of the contamination has been determined to be the refiner of the avgas. Through its distribution system, the refiner inadvertently caused Jet A fuel to be loaded into distribution tanks intended for avgas. Contaminated avgas from these distribution tanks was then shipped to local fuel distributors. The FAA has determined that aircraft with certain Franklin engines installed were fueled with this contaminated mixture between May 22 and June 2, 1994, at Sacramento Executive (SAC) airport, or between May 18 and June 2, 1994, at Sacramento Metro (SMF) airport. The list of U.S. registered aircraft specified in the applicability paragraph of this AD is based on investigation of fueling records secured from the two affected airports, which the FAA has determined to represent the population of affected engines. That condition, if not corrected, could result in detonation due to low octane, which can result in severe engine damage and subsequent failure.
This AD requires engines certified to operate on 91 octane or higher avgas to undergo a teardown and analytical inspection for detonation damage, and engines certified to operate on 80 octane avgas to undergo inspection for evidence of possible internal engine damage. Engineering analysis of operating these engines with avgas contaminated with Jet A fuel indicates that actual damage to the engine may range from unnoticeable to very severe, according to the duration of run, engine power level, and level of contamination. Damage may be characterized by increased operating temperatures resulting in damaged intake valves and burned pistons, and excessive loads imposed by detonation. Since internal damage may not be assessed by any other method, engines certified to operate on 91 octane or higher avgas must undergo a teardown and analytical inspection and any parts showing signs of detonation damage must be replaced.

This is the first AD I found. . . there are several others to cover this issue. You can find them at www.faa.gov . Search for Airworthyness Directives, key words contaminated fuel.

Just wanted to show I wasn't making this shit up.

BK