Engine Mechanical problem
1977 Oldsmobile 442 V8 Two Wheel Drive Automatic 0
I have a 1976 Olds 350cu in engine. We have completely rebuilt the engine and turbo 350 transmission. It runs fine but when the engine is cold it hold oil pressure @ about 50 psi but when it warms up it drops to 1 or 2 pounds at idle. When you up the RPMs the pressure comes back up to 20 psi. We have replaced the oil pump with a high output pump, new sending unit and gauge and replaced the oil with a 10-30 penzoil to see if the other oil was not qualitity enough. We took it to our mechanic and had him check the pressure with his gauge and it did the same thing. We took the top end off and check to make sure the engine shop replaced the plug to the timing gear galley, we spun the oil pump with a drill and we were getting good oil flow in the lifters, distributor port, and through the cam bearings. We are pretty sure that the main bearings are ok as we were careful checking each with plastic gauge strips and specified torque. We don't see any wear on the cam or lifters after the break in. Do these Old Olds engines run low oil pressure and are we chasing a ghost? Are we missing plugging an oil galley somewhere on this engine?
The spec is 30-45 psi at 1500 rpm, retest pressure with these specs.
May, 11, 2010 AT 11:17 AM
We have tested it several times. The problem is low oil pressure at idle when hot. 1 or 2 pounds. When revived hot it will only go to 20-25 pounds. It's ok when oil is cold. It appears oil is pumping every wear it should. I would think the main bearings would have to be pretty loose to lose oil pressure? I doubt that because we just installed them with plastic gauges and two differant torque wrenches. We have examined the top end and can not find any plugged galleies or missing plugs to the timing chain area. We had a MSD distributor on a chevy 454 that said it didn't need o rings but after we installed some that ended a similar problem. This car has the orginal distributor and the oil gallies do not go through a ring on the distributor lick the Chevy. Do you know what the OEM oil weight was for this engine?
May, 11, 2010 AT 11:42 AM
You do have a bearing or crank journal wear problem, two different pumps and both have low pressure. Not sure what oil was used new, but if the engine was just rebuilt, it's way too low. You could try SAE 30 and see what happens. Just lighten it up some during the winter.