I have changed my oil with the same container and have never had it overflow, until this last time, by about a quart. I know that I don't have coolant in the oil. Is there a way that diesel can get into the crankcase, the oil was pretty thin. maybe by the pump or the injectors. Early, 1991 without intercooler and 727 trans. 215k on the engine. Any ideas.

 

I would seriously consider having that oil sampled before you throw it away if you haven't already. Yes, diesel can get into the crancase by several methods.

 

Agree with Dieseldude4X4 get a sample in for testing asap .... diesel fuel can wipe your bearings and cause failure

 

fuel can get into the crankcase when an injecter is seeping a little when you are shut down. it will just drip into a cylinder and wash down into the oil. i haven't had my cummins do this but have had a detroit and a cat do this in a couple of heavy trucks.

 

Agreed, get an oil analysis ASAP. If you plan on continuing to drive your truck then suggest that you check your oil level daily. If it starts to rise, then time to change the oil again before you ruin the engine. Best bet is to trace the cause as fast as you can and not drive it very much until you have the cause rectified.
You could try pulling all the injectors and having a look to see if one is wetter than the others.

 

Bad lift pump, leaking into engine from bad diaphram. Its a cheap insurance fix. 35 bucks or so.