This is a real brain teaser. I've a 98.5 with 125,000 miles on it, this has an excellant truck except for one thing, it loses engias ne oil through the vent tube. It always does this on level surfaces at speed, but, it occurs randomly. I brought the truck at least six mechanics no one has been able to figure this out. The compression is good, it starts up fast, the fuel economy and power are excellant, the turbo is in good shape it has been ruled out, it has never run hot even in 100deg+ temperatures. It will do this with or without a load. For practical purposes the engine works great except it blows engine oil and all at once. If anybody has any idea PLEASE tell me.

 

You're not overfilling it with oil are you?


phox

 

I had the same thought as phox. If you have the chance check your dipstick and the markings against a dipstick from a similar truck.

 

I did check the dipstick with another, as it turns out there was a recall on this particular dipstick. The previous owner never changed it for the five years he owned it. A mechanic showed me this problem and i filled to the word "add", (the correct level). After a week everything was fine, then I noticed another leak coming from the diaphragm on left side of the engine. it was replaced. Then during a couple of test runs the problem came back and I have truck parked. When the engine was apart everything looked clean, including the screen that went to the vent tube. I have mechanic looking at it now trying to figure this one out.

 

I was told from the service manager at Cummins, check your vacuum pump as this will cause blowby and therefore oil loss.