take this with a grain of salt , but I would go to a synthetic oil of a lighter weight vs. pulling a engine just to see what happens . So I assume there is no unusual engine noises? Do you think that the engine has been serviced well, not being sledged up , if so a high detergent lighter oil might help clean things some. good luck
Still haven't gotten to the bottom of this one, but have discovered a few things: 1. I've verified pressure gauge to be reading correctly, by attaching gauge to known pressure source. And after running the engine for several days this past summer, I definitely get oil leakage around the sender unit and oil filter (no matter how tight I get it). Not a good sign, and I'm afraid something is going to 'blow,' like the oil pump, causing engine damage, or leaving me stranded. 2. I'm supper happy to report, however, that you CAN assess the oil pressure reliever valve (spring, poppet) WITHOUT removing the engine. The oil pan can be dropped and pulled out around the oil intake screen/tub, with no problems. Then the valve can be easily accessed as it's right there in front. Easy Peesy! Note: the back two pan bolts were not accessible with a socket or wretch, but the bolt heads have a Phillips driver as well, so with a short Phillips they can be unscrewed. 3. There was no 'obvious' excessive damage. However here's what I've determined on that. There is a spot of some wear on the poppet with some small scratch marks that can be felt with a finger nail. I'm assuming this could be causing the poppet to 'stick' and not release at proper pressure. I'm not sure if the valve assembly is intended to regulate pressure, or only for excessive pressure release? Anyone know about that? Just the same, the spring, does not appear to be within specs (Free Length 1.850 inches, Pre–load 16 lbs. @ 1.398 inches). I don't have a spring compression tester, but with my 'home-made' job I am getting slightly more pre-load (in the 18-20 lbs) to achieve the 1.4 inches in compression length. Also it measures a bit short for Free Length = 1.702" Soln? I'm hoping I can get replacement from Napa. My understanding is the Mitsubishi 4G3 engine was also used in the Mirage and some of their forklifts. If I could find the part number that could be helpful. Outside of that, I'll have to try polishing the scratches out of the poppet and give that a try.