The fuel pre heater is using the engine coolant for function. So engine oil is not mixing with the fuel there. Well if the oil under pressure is higher than the internal lift pump pressure it can flow into the lift pump. If the O ring is bad.

My guess is the available oil pressure lubricating the injection pump is higher on that series of engines in the injection pump. Basically less lubrication flow restriction than the earlier injection pumps. A heavy flow meaning more oil pressure is present perhaps.

That is only a guess though as on the earlier engines the fuel tended to flow into the engine diluting the engine oil in the process. The engine oil level would rise.

With the black appearing fluid logically being engine oil added to the fuel. A smoky burn is to be expected. That used engine oil burns dirty is well known.

If you had not mentioned the change in the fuel color. Or it was not observed and the signifigance of it understood. You could have undergone a horrible experience finding your issue.

My overall point is there is no way to expect to see the color of the fuel changed in the way you describe. As a normal situation.


I am heavy on diagnostic testing. If you disconnect the output line on the lift pump. Collect a little fuel by cranking the engine. With the shut off tied down on the injection pump.


So the engine does not start. It probably will not anyways. If that fuel sample is darker . Remove the lift pump to see if you can change that o ring in that model of lift pump. You probably can.


Also if it turns out to be the issue. Change the engine oil as some fuel may have thinned it.


It sounds like you have located a really nice example of the model.