The Cummins ISC Diesel Engine is a great performer, we have several in our fleet and they are a very durable diesel engine. As with any engine there are failures and in this case we experienced the oil level increasing to an over full condition. One test that told us it was fuel in the oil was the oil sample analysis. We took a sample and the guys at BTA in Kamloops faxed over a report to let us know it was in fact diesel fuel. Another tell tale red flag was the oil pressure was dropping below normal along with a splatter of oil on the rear engine compartment door. The viscosity decreased making the oil thinner causing these conditions. We actually went through this repair before and the symptoms were exactly the same (that’s what happens when you have a fleet with the same drive train). The CAPS Fuel Pump has to be replaced to repair this condition since it provides the high pressure fuel and injection delivery. It runs directly off the accessory gear and is about the same size as a 2 cylinder air compressor. The fuel lines and accessories have to be removed along with the pump accessory drive gear. The first thing to do after this repair is change the engine oil and get rid of that thinned out engine oil.