BobM46128

We just bought a '91 GMC Sierra extended cab. It was super clean, not just cleaned up, under the hood. The spark knock sensor was broken when they installed the new starter and we put a new one on just before taking a 400-500 mile trip. It would have been a longer trip, but at about 250 miles we discovered we were loosing LOTS of oil. It took 8 quarts to get us back home! The oil pressure stayed around 45-50 lbs and we had no oil starvation noises.
When we got home we looked fruitlessly for a leak, but no luck. The exhaust is spewing diesel black oil out of the exhaust. then we looked into the radiator and found white foam!
I'm guessing that we have a cracked head or head gasket. Any one had this problem before? And would I be alright just redoing the heads and head gaskets? The truck sounds really healthy and the oil pressure is staying around 45-50. Any ideas?

horse482

It does sound like a head or head gasket problem, but they usually don't dump oil in to the combustion chamber. It is posible that the head has a crack big enough to dump oil in to the coolant and a crack around one of the exhaust valve guides. About the only thing that you can do is pull the heads.

BobM46128

Yeah. I filled the heater and turned it on, so I guess I've got no more excuses! So I'm headed out to the garage.
I bought it cheap and I guess I got what I paid for!

Riche

try pulling the spark plugs and finding the cylinder with the oil... the plug will be covered. If oil is not the plugs then the leak is can not be in the cylinders. It may narrow the search down for you at least.