Diesel fuel, how old is too old?

[Raspy]

There is a difference between fuel going "bad" and contamination. It seems that diesel doesn't go bad and I've burned some in my boat and my old Mercedes that could have been 40 years old. It had been sitting in an old tank for heating oil on a friends property. No problem. But algae is a problem and it gets in from the tank breathing. Moisture in the air comes in when the tank cools and heats repeatedly. It gradually builds up to a puddle in the bottom and then algae grows to become a black sludge that will clog filters. Any fuel that will be stored for a while, or gets used very slowly, should get a biocide added. Also a water separator of some kind before the filter. A water bowl is OK, or a drain valve on a tee, or something that can get maintenance. But a water separating filter can get overwhelmed and let water go right on through. Be careful. I ended up with water in my injectors because of that.

Fuel polishing sounds good on paper, but the sludge sticks to the tank bottom and most likely won't get hosed off in a typical tank. Best if you can take off an inspection cover and spray out the interior of the tank with the filtered fuel as it gets recycled through the polishing equipment. Most boats don't have inspection covers and the tank is at the end of a long curving fill tube. It's usually done on boats that have been sitting for a long time and are about to go on a trip. In that case the owner should take a couple cases of filters because the boats motion stirs it all up and sends it to the filter.

 

[txdon]

I have a friend, I'll call him "Fred" , who is using 18 year old diesel in his new Kubota and having power problems. He says the old diesel is not the problem and has narrowed it down to an air problem. Can diesel still be good fuel after 18 years?

 

[California]

How can he have an air problem when a diesel's throttle is wide open all the time? I would still suspect a clogged fuel filter or line.

 

[kevin37b]

You mean fred and the famous turbo fi x ?

 

[txdon]

Yes, Turbo Fred. but this is not about his turbo thread, I was just curious about the longevity of diesel fuel.

 

[Raspy]

How can he have an air problem when a diesel's throttle is wide open all the time? I would still suspect a clogged fuel filter or line.

Simple, it's called a clogged air filter, or a bird in the intake horn, or a disconnected turbo boot, or a bad barometric compensator, or a kinked exhaust. That may not be the problem, but air can definitely be a problem even though the intake is always open. Not enough air will cause black smoke, clogged fuel filter will cause loss of power, erratic running and possibly blue smoke.