HOW LOW CAN YOU GO?
I’ve read a lot of your Q&A tech. You guys are the absolute experts. I own a former U.S. Army Humvee equipped with the 6.5L GM diesel engine. The engine has a problem, and I’m hoping you can help.
The problem is very low pressure when the engine is warm. The cold idle oil pressure is about 25-30 psi, but as the engine warms, the oil pressure drops to near zero.
I have already changed the oil pump and looked at a selection of crankshaft bearings. All appear normal (the engine has accumulated just 20K miles since being rebuilt in 2006). I thought at first that the dash gauge was reading incorrectly, but I have verified the oil pressure problem using a known-good mechanical oil pressure gauge.
Do you have experience with such a failure?
Andy Dreschner Germany
The AERA Technical Service Bulletin #1180 indicates that owners of 6.5L diesel engines with oil pressure of less than 10 psi at a hot idle or 40-45 psi at 2,000 rpm, and assuming all other sources of oil pressure loss have been eliminated, should do the following.
Remove the water pump and aluminum front timing cover to verify that the camshaft oil gallery plugs are not dislodged or missing. A missing plug would cause a loss of oil pressure and a massive oil leak internal to the engine. There are other inspections called for if one or both cam oil galley plugs are not intact, like verifying whether the #1 main bearing or turbocharger shaft bearing have been damaged due to oil starvation.
Some time ago we visited AM General’s engine manufacturing plant in Franklin, Ohio. While there we saw how they pre-test an engine to ensure that all of the bearings and related oil galley plugs have been installed before they complete engine assembly. Basically, they used air to pressurize the lubrication system, then looked/listened for an unusually large air leak. Normally, there’s just a lot of hissing around all of the bearings. A missing bearing or galley plug would cause a loud rushing of air.
Aside from an engine teardown, we don’t know what else to suggest. You may need to remove the engine, pull it apart down to the short block, then pressurize the oil system, looking for a large air leak. Good luck, and keep us posted.