Gene Peterson

My 1991 Dodge cummins runs great but gets water in the oil. Replaced oil
cooler. Same problem (water in oil and oil in water) Whats happening?

wannadiesel

Welcome to DTR.

Water "water" or coolant "water"?

If it's coolant, then it sounds like you need to change the head gasket.

timeagain

Yep head gasget, or a cracked casting.

Lil Dog

You also have to be careful with the earlier series engines. The 89-91 non IC models had 9mm injectors and there is potential (very small) for a cracked head. However the cross over of oil to glycol and vice versa is typically an oil cooler problem.

The water and oil don't meet until cooler, so you usually don't see cross contamination from a head gasket leak.

von Trapp

"Usually" being to operative qualifier

It is quite possible to have a HG blow out the gasket material between an oil passage and a coolant passage opening. This problem happened 3 times on my FL70's 5.9L before we figured out WHY it was happening (a long story for another post LOL)

Oil cooler is the first suspect. Pull it off, and pressure test the sucker.

If it tests OK, I would go to NAPA (or alternative) and rent a coolant pressure tester. Run up the psi, and see what the drop rate is. You can try pulling the valve covers, and listen for a "hiss" noise. You might get lucky and actually see or hear a leak, especially in the pushrod holes, which are very close to coolant passages on the 5.9L head. It's nice to be able to know the general area of a leak, so you can look more closely at the head/HG/block when you have it all apart.

Pulling the head on a 5.9L is not that hard; it's pretty straightforward. Hopefully you have a Dodge service manual in your possession. Head bolts are 18mm, and very tight. You should use a big breaker bar to make life easier, and better yet, make sure the engine sits for at least 6 hours to cool off. I'd also recommend using a cherry picker to lift the head off. It's a heavy SOB. You can leave the exhaust manifold and turbo on the head BTW.

There is a head gasket kit available from Cummins and Dodge; comes with almost every gasket you'll ever need on the top end, including new fuel return line washers and a head bolt stretch gauge. Either may sell you a single head gasket too, but the part number seems to get "lost" sometimes...guess because a single HG is less money than a HG kit

Shop around other sources too; some engine rebuilders also sell parts.

Make sure to take the time and have the head pressure tested / magnafluxed while it's off.

Piers had a special on heads; might still be available.

Gene Peterson

Appreciate the infom, these diesels are the only way to go! I was gonna give up and went out bought a used Dodge 2500 (v-10 engine). Its up for sale now due to 9 miles/gallon OUCH!

Gene