91 Lumina Sedan - 174,000Km

I have a problem with high oil pressure. Once the engine warms up, if I am cruising between 100-120km (60-70mph) @ 2000rpm, my oil gauge reading is way up in the high end sometime touching the 550kp mark(highest mark on gauge). If I'm going up a hill the pressure drops ever so slightly but after cresting the hill (engine now not working as hard) the pressure increases again. The needle also fluctuates a little in the high end from time to time despite being on cruise control and the rpm being constant. I have had the oil and filter changed but still have the problem. This all started when I began using 5w30 synthetic oi during the winter and regular 5w30 for the summer 18 months ago.

Anyone have any ideas?

Andy

Well first thing, once you go synthetic your not supposed to go back to normal oil. Synthetic has detergants which clean out the engine and help protect against friction better than regular oil does, it also conditions seals but if the seal is allready shot it cant do anything for it. On an engine with 100,000 + miles thats not a good thing. The synthetic will break down any deposits and gunk inside there, and they will all float around in your crankcase until the next change. You dont want tar and chunks of burnt oil floating around in your engine. It will do this until the engine is clean, but it will also eat away the gunk around the seals, which maybe holding back a huge leak.
Why would you use the same weight synthetic in the winter as the regular oil in summer? That doesnt help it any. Your supposed to use higher weight oil in the summer.
For the oil pressure problem. You may have to much oil in it, or your oil pressure sensor is fudged. Most likely the sensor, but check the oil anyway.

I'll point out 2 things you may be seeing. First off in the GM 2.8 engine in the late 80's they had a crank bearing clearance issue where they had too much clearance so they ran more oil pressure to compensate for the problem. If I'm not mistaken the 3.1 had a similar issue, but I am not sure the year it was cleared up. The other more likely thing you are seeing is the pressure sender for the gage is out of calibration. Put a new sender in it. It may be reading abnormally high.















91 Lumina Sedan - 174,000Km

I have a problem with high oil pressure. Once the engine warms up, if I am cruising between 100-120km (60-70mph) @ 2000rpm, my oil gauge reading is way up in the high end sometime touching the 550kp mark(highest mark on gauge). If I'm going up a hill the pressure drops ever so slightly but after cresting the hill (engine now not working as hard) the pressure increases again. The needle also fluctuates a little in the high end from time to time despite being on cruise control and the rpm being constant. I have had the oil and filter changed but still have the problem. This all started when I began using 5w30 synthetic oi during the winter and regular 5w30 for the summer 18 months ago.

Anyone have any ideas?

Andy

Oil pressure sender kaput.