Mistakenly put diesel in fuel tank

[PDW911]

1999 250 HP Alpha

I messed up and put approx. 25 gals of diesel in my 100 gal tank that had 25 gals or so of fuel. Obviously the boat stalled and quit. After a tow to our dock, the dock mechanic (not my regular technician) drained fuel tank, changed fuel separator, "cleaned carb" and filled tank with 50 gals of fresh fuel. When I picked up boat he said it was still stalling off/on and back firing now and then, but to run it and it would straighten itself out

I ran it for about 40 minutes with various levels of acceleration...it still runs rough, the RPMS don't peak out any higher than 3800 (usually I get a good 4200-4400), it occasionally back fires or hic ups, idles rough, stalled going in reverse, difficult to start, but ultimately did......although the more I ran it...it seemed to get better (wishful thinking??)

Any way I am about to pull the boat and take it to my regular mechanic....just wondering, was running it OK....I'm concerned about doing any damage (or making it worse) by running it and there isn't a lot on the web about what to do in this situation

(I never noticed the green hose......my mistake for sure)

Any meaningful comments or suggestions really appreciated

 

[Scott Danforth]

Re: Mistakenly put diesel in fuel tank

It sounds like there still is diesel fuel in the system. did the plugs get changed? the diesel fuel would have fouled the plugs.

you didnt hurt the motor, just your pocket book. now it you put regular fuel into a diesel, you would have taken the motor out.

 

[NHGuy]

Re: Mistakenly put diesel in fuel tank

More info please, is it really a carburetor engine? or EFI? If it's a carb motor put new spark plugs in it, change the oil and give it a go. Change the fuel water separator often, and run the gas down to near empty before each fuel stop.
How does the engine oil look and smell? How is it's level?
If it never gets all the way better you might need to redo the carb further than a clean up. Might need a true carb rebuild. The diesel could have plugged or stuck in places in your carb. It could have cleaned up stuck stuff in the carb which then clogged smaller openings. Or it possibly could have deteriorated the float or the accelerator pump seal. I'd at least run it at big throttle openings, like almost wide open, til it stops improving.
Or just do the carb, oil, separator, and plugs. You'll probably do them anyway eventually.

 

[Southtowns27]

Re: Mistakenly put diesel in fuel tank

Likely fouled the spark plugs...change them out and try it again. The diesel really shouldn't have hurt anything.

 

[HT32BSX115]

Re: Mistakenly put diesel in fuel tank

I messed up and put approx. 25 gals of diesel in my 100 gal tank that had 25 gals or so of fuel. Obviously the boat stalled and quit.

Howdy,


When the engine "stalled, and quit", did you hear any detonation/pinging? If you did, you may have more problems that new plugs won't fix.

Did you remove the spark plugs and crank the engine to purge any water that may have been "sucked" back into the engine from the "sudden stoppage" ?

Marine engines are not unlike aircraft engines. (running at high continuous HP for long periods of time) When gasoline aircraft engines are misfueled with Jet-A (kerosene based fuel not unlike diesel), it nearly ALWAYS causes detonation and complete engine failure. You cannot "hear" detonation in an aircraft engine.

It's very hard to hear detonation in marine engines and frequently, the damage is "done" before you can throttle-back & get it shut down.

After you inspect/clean/replace the plugs, you may need to do either a cylinder leak-down or a compression check to verify the integrity of the cyls.


Regards,


Rick

 

[Walt T]

Re: Mistakenly put diesel in fuel tank

Diesel wont detonate in a gas engine and in fact will raise the octane of the gas to a point where it may not even fire in the engine. This is what is happening now. I'm sure there was still some diesel in the tank even though the mechanic said he pumped it. Sorry but running it and doing what NH said about all you can do. You can also just pump all the gas out and sell it to some unsuspecting lawn care guy but you shouldn't have to rebuild the carb. Diesel will not foul it. It most definitely can foul spark plugs so check them.

 

[agallant80]

Re: Mistakenly put diesel in fuel tank

Diesel wont detonate in a gas engine and in fact will raise the octane of the gas to a point where it may not even fire in the engine.

You mean lower? Diesel is 40 Octane.

 

[HT32BSX115]

Re: Mistakenly put diesel in fuel tank

Diesel wont detonate in a gas engine and in fact will raise the octane of the gas to a point where it may not even fire in the engine.

Only true to a point. Diesel fuel won't "ignite" in a gasoline engine if the fuel is 100% diesel (or kerosene)

But, diesel fuel in gasoline is like any other oil in gasoline........... IF introduced at high power settings (like full throttle) and if the engine was able to make it to full power before the contaminated fuel made it to the induction system, there will likely be detonation when the fuel DOES get to the engine.

If the contaminated fuel got into the carb(s) BEFORE the engine(s) made full power (and max combustion temps), THEN they were likely UNABLE to get to full power. AND there *should* be no damage. (other fuel system contamination and plug/combustion chamber fouling)

There is no "octane" number for diesel or other kerosene type fuels it's a completely meaningless number for anything other than gasoline or other high vapor-pressure or gaseous fuels.

 

[PDW911]

Re: Mistakenly put diesel in fuel tank

More info please, is it really a carburetor engine? or EFI? If it's a carb motor put new spark plugs in it, change the oil and give it a go. Change the fuel water separator often, and run the gas down to near empty before each fuel stop.
How does the engine oil look and smell? How is it's level?
If it never gets all the way better you might need to redo the carb further than a clean up. Might need a true carb rebuild. The diesel could have plugged or stuck in places in your carb. It could have cleaned up stuck stuff in the carb which then clogged smaller openings. Or it possibly could have deteriorated the float or the accelerator pump seal. I'd at least run it at big throttle openings, like almost wide open, til it stops improving.
Or just do the carb, oil, separator, and plugs. You'll probably do them anyway eventually.

Yes it is a carb....not EFI. The best I can gather is that dock mechanic did not change plugs or oil. I am guessing that my mechanic will do so ( I discussed briefly with him this AM)...but he didn't comment about the back fire or roughness. he doesn't want me to do anything until I get him the boat

 

[PDW911]

Re: Mistakenly put diesel in fuel tank

Yes it is a carb....not EFI. The best I can gather is that dock mechanic did not change plugs or oil. I am guessing that my mechanic will do so ( I discussed briefly with him this AM)...but he didn't comment about the back fire or roughness. he doesn't want me to do anything until I get him the boat

I appreciate all of the input.......bottom line...it appears it would run rough until all of the remediation steps are performed. It was a little early to pull the boat, but with weather changing I'm only losing a couple of weeks. I trust my normal mechanic so I assume if he thinks the carb needs extra work, he will do so. He did indicate that the fuel tank was probably run down to no more than a gallon or two of 50% mix of diesel and gas. With a full fill (100 gallons) of gas, the mixture will probably mix out to 1% contaminated...and lessen as I add fuel

I was more concerned about major damage to the engine...I guess it will run a little rough in the spring

 

[Walt T]

Re: Mistakenly put diesel in fuel tank

You're right Agallan, I should have said Cetane

This explains it pretty good:

The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking.

 

[crazy charlie]

Re: Mistakenly put diesel in fuel tank

Replace the plugs and change/drain the fuel water seperator again and replace the fuel filter in the carb and you should be fine.Charlie