Mysterious Corrosion in Cat D4 Fuel Tank

Hello ACMOC members:
I'm having problems with a 30 gallon diesel fuel seat tank on a Caterpillar D4 (7U series) tractor. This tank slowly accumulates a corrosive brown residue under the fuel cap that eventually destroys the ring (Caterpillar P/N: T-22, RING) that holds the fuel strainer in position. Further inspection shows more of this residue inside the fuel tank above the fuel level. This residue is also pitting the metal under the fuel cap at the top of the tank. The fuel tank cap is new and the tractor is stored indoors when not in use in the Redding, CA area. The yearly temperature in the storage building ranges from about 35 to 95 degrees Fahrenheit. The altitude at this location is about 3600 feet and the tractor sits most of the time. The fuel is acquired locally and is sold for agricultural use as "red dyed" diesel fuel. The tank was previously cleaned (over 10 years ago) at a local radiator shop and we have installed a Caterpillar diesel fuel filter between the fuel tank and the fuel transfer pump to protect the pump. Do any of you folks know why this residue is appearing and how it can be prevented? Thanks from realwork.

I get that stuff too.

I get the feeling it is something that happens with diesel fuel, like it is the result of the fuel evaporating in the tank and drying at the top of the filler hole.

I think it is "normal" but I would also be interested in knowing if someone actually knows something about it.

Looks like typical rust from condensation. If you are able to store the tractor with the diesel tank full, it really helps this sort of thing.

Hope this helps

BP.

Its from not keeping the tank full. any air space in the tank is room for condensation.

yes my D4 does that too. i think this new diesel is to dry to prevent corrosion like old N0.2 fuel used to do. i just pour a little ATF around that area before i park the tractor and it seems to help.

Rust, plain old fashioned rust.

Rust as evidenced by the fact that the bottom of the filter can be seen! :doh:

[quote="realwork"]Hello ACMOC members:
I'm having problems with a 30 gallon diesel fuel seat tank on a Caterpillar D4 (7U series) tractor. This tank slowly accumulates a corrosive brown residue under the fuel cap that eventually destroys the ring (Caterpillar P/N: T-22, RING) that holds the fuel strainer in position. Further inspection shows more of this residue inside the fuel tank above the fuel level. This residue is also pitting the metal under the fuel cap at the top of the tank. The fuel tank cap is new and the tractor is stored indoors when not in use in the Redding, CA area. The yearly temperature in the storage building ranges from about 35 to 95 degrees Fahrenheit. The altitude at this location is about 3600 feet and the tractor sits most of the time. The fuel is acquired locally and is sold for agricultural use as "red dyed" diesel fuel. The tank was previously cleaned (over 10 years ago) at a local radiator shop and we have installed a Caterpillar diesel fuel filter between the fuel tank and the fuel transfer pump to protect the pump. Do any of you folks know why this residue is appearing and how it can be prevented? Thanks from realwork.[/quote]
It would be worthwhile to keep tank always supplied [and kept full of fuel] with a supplement fuel deicer [heet]no matter what time of year,
eventually tank will most likely rust threw on bottom,this is how all of my equipment is maintained.

my opinion,which is always free,leon

Yep wet rust, This is why i filter the fuel b4 it gets 2 the transfer pump using a felt oil furnace filter.