Bad fuel cleanup help needed

So I messed up. I forgot to add stabilizer to the diesel in my 802 when I filled it about 9 months ago. Now the diesel has varnished up and coated the inside of the tank. Well I didn’t discover this until after I had ran the generator for about 3 hours. Now it ran just fine, and still does, but now what?

I’m removing the old fuel but what is the best way to remove the varnish from within the tank? I plan to change the fuel filters but is there anything else I should do?


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This is my opinion and your mileage may vary. If it were me I would dump the old fuel change the filters and fill it up with new fuel and stabilizer. While you’re at it go ahead and service the engine as well.


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I have found that E85 will dissolve that varnish. Fill the tank 1/3 full and let it ride around with you for a few days to let it slosh around and dissolve the gunk.

NDT said:

I have found that E85 will dissolve that varnish. Fill the tank 1/3 full and let it ride around with you for a few days to let it slosh around and dissolve the gunk.

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Ride around? It’s in my mep-802. I’m more or less concerned about potential damage to the injectors or mechanical fuel pump. I just need to get this figured out before winter in case we get any ice storms and I need to use the generator.


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Diesel doesn't turn to varnish, what you see in your tank is wax.If the fuel isn't agitated over long term storage some of the wax will settle out. This seams to be more pronounced with ulsd as the lubricity agent can also fall out and collect on the sides of the tank. What you have in your tank will not hurt your fuel system, aside from maybe plugging a filter. just run it, many times I have started a diesel engine and run it after being parked for many years, I just run the tank empty refill it than change filters.

I should add water will damage your fuel system if water ends up at the injectors than the pintles will get scored and stick because of a lack of lubricity.

snowtrac nome said:

Diesel doesn't turn to varnish, what you see in your tank is wax.If the fuel isn't agitated over long term storage some of the wax will settle out. This seams to be more pronounced with ulsd as the lubricity agent can also fall out and collect on the sides of the tank. What you have in your tank will not hurt your fuel system, aside from maybe plugging a filter. just run it, many times I have started a diesel engine and run it after being parked for many years, I just run the tank empty refill it than change filters.

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This is my experience as well. If this were a truck and I was going to driive it 1000 miles I'd just take off and go and top the tank off with fresh fuel in about 50 miles and then again at 1/2 a tank.

If it's a genset that's going to sit prior to use, you can drain the tank and replace it with fresh treated fuel, but understand that what your treating is owner anxiety and not a real problem...

Ok. Well that makes me fill better. However I still need to do something as things are so sticky inside the tank that the strained at the end of the fill port won’t even drain fuel when pulled out.


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its just wax which is good for your system anyway the only way to get rid of it is a solvent I would blow backward through the drain to get the drain to work or if the genset is on a trailer take it for a field trip, and slosh the fuel around. I have tried to remove that goo from plastic ibc containers with a steam cleaner and it wont even touch it.

Well I went ahead and treated my 55gallon drum again with another dose of PRI-D and shook the drum around for a few minutes. Hopefully that staves off having the same problem with the large reserve.


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I attached a picture of the super sticky sludge I pulled out of the tank. It’s only a little bit but there’s plenty more in there. Unfortunately it completely gummed up my fuel gauge probe, and the fuel level float are pretty sticky as well. So when I have time I’m gonna have to drain the new fuel I put in there and somehow clean that stuff out.

I managed to pull the filler tube out of the filler neck and cleaned off the strainer with a blow torch and wire brush. Worked pretty good.


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I am not sure what that is. My MEP-003 sat for 4 years with a 3/4 full tank on a yard and there was a little crud / sediment in the bottom of the tank but nothing that was close to that mess.

I would pull the tank and see how much of that you could get out.


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that looks like an extreme case of algee

snowtrac nome said:

that looks like an extreme case of algee

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I thought that at first but it just doesn’t look like a biomass. It’s most closely related to a tar substance unless you let it dry out and then it’s like a wax.


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Those fill strainers can get clogged quite easily...but that does look bad. I soaked mine in Mineral spirits, paint thinner then blew it off with a blow gun. Thats how i cleaned my fuel tank too. although to clean the bottom of the tank i did have to stuck my arm in there with a rag and rub the bottom. My fuel system was no where near as bad as yours. I was in there to do the well nuts or else i wouldnt have done anything.

You could pull out or tie up the fuel senders/float, put some solvent and a chain on a string in the tank and go for a drive. The chain scrubs the bottom and the string lets you remove it easily.

Ops double post.

Howdy,

I know what you have.


Somebody used a bunch of black RTV which has since dissolved in the diesel.

Daybreak said:

Howdy,

I know what you have.


Somebody used a bunch of black RTV which has since dissolved in the diesel.

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Let's hope not....

Daybreak said:

Howdy,

I know what you have.


Somebody used a bunch of black RTV which has since dissolved in the diesel.

Click to expand...

I don’t think so. When I first got this unit I tore it apart to replace the leaky well nut. Cleaned the tank on the inside very well. Never saw any RTV sealant. This really seems to have come from the fuel. The fuel itself smelled and felt different in between my fingers from fresh stuff.


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I have posted this PDF document before, however it's not easy to find buried in older posts so I am posting this again as it seems relevant. This document is from BP Australia, so keep in mind their seasons are opposite as ours where winter months are mentioned. This document is intended to address bulk diesel fuel storage for large fuel consumers like Australian ranches/farms etc. However the information is useful for long-term diesel fuel storage regardless.

View attachment long-term-storage-diesel.pdf