I have a CAT Grader S/N is 71D438 (1959 or 1960 model) It's old but still strong.
Trouble is: there is some fuel leaking into the oil. Not a lot but enough to be concerned about. I can run it but would rather not because it thins the oil too much.
A mechanic said it might be a seal at the fuel injection pump to the block.
Any ideas on what the problem might be or how to fix this?
Please click on the photos below to enlarge the view of the fuel pump housing attached to the block.
Is the 'seal' or 'O-ring' that needs replacing visible in the diagram? (part #)
This forum has helped me before and I'm confident with the info I get here.
Thanks, Ol George

Yes, that is a common problem with these old Cat's....The "O" ring that seals the fuel chamber at the joint going from the filter housing to the fuel injection pump housing drys out/shrinks, allowing fuel to leak down into the sump. You will have to pull the fuel injection pump/governor assembly to access. Should only be one seal on the late D318 where the earlier ones have the same seal at both ends of the pump housing that should be replaced together.

I have added a photo and diagram; can you see which part needs replacing?
Looks like it might be part # 1H5959 which is listed as a 'seal'.

Obviously, I'll need to bleed the system when done, but I was thinking I could do this repair myself... What do you think? I have already fixed one seal to one of the injector pumps. If I can manage this repair, I might as well replace the remaining five. Maybe....

The seal I'm referring to is a 8B4967....you have to look at the fuel injection pump housing diagram for the part. Would be a good idea to replace the 1H5959 also while your in there.
No reason you can't do the repairs, it's pretty straight forward, just a little awkward to get the nuts on the back side.

I think the seal you need is an "O" ring seal and is toward the top of the front housing where the tube (ferrule) sticks out and is a 8B4967 and you,ll need a new gasket too when you take the housing off. It would be a good idea too to change that lip seal at the bottom that slips over the drive for the camshaft to drive in the lower housing. That is the 1H5959 and the gasket for the front of the housing is 4F5148 where the inj. housing bolts to the front filter housing. Also the transfer pump seals can cause fuel to get in the diesel oil so you might want to replace them too.