Mysterious low oil pressure problem

[stevembraun]

I have a 1997 850 GLT, my Volvo. I kicked my Subaru to the curb this summer, because I hated how it handled in our 6 month long Minnesota winter. I got my 850 for a song over the summer, knowing it was in need of love. So I replaced all the brakes, the front suspension, ABS module, timing components, and transmissions fluid over the summer. A local mechanic replaced the starter, because the previous owner had problems with it. His mechanic, come to find out, put the wrong starter in. Fast forward to the winter, when a trip to hell is more preferable then crawling under your car when the ambient air temperature is south of 10 below. My oil pressure light started going on and off at start. Nothing major. It was really cold. Then, when I was driving home one day, it started flickering on and off, which freaked me out. So until my tax return came, it visited opposite sides of the street every week. It went to visit the local Volvo mechanic Tuesday, who I may still be donating my kidney to. Sure enough, my oil pressure was low. He dropped the oil pan, and replaced the o-ring to the pick up tube. Checked the oil pressure. It was good. Yay. Took it for a spin. Low oil pressure light. The newly increased oil pressure blew out my crankcase seal and the seal behind my distributor and the seal around the oil pressure sending unit. Expected. Told him to replace them and check my PCV system, because I didn't want to be blowing seals. So he replaced my seals and my breather system. Took it for two test drives between 5-10 miles. First one, fine. Second one, the light came back on. He's stumped. I don't know everything they've checked after this third attempt. Perhaps another seal is leaking, and there is a low oil in general in the system? If the sensor was bad, would it be on right away, instead of waiting ~15 miles. Also, I wish he would have called me when the pan was dropped, because I would have had him replaced all the seals/o-rings in the oil sump. Any thoughts? Silver linings, it's now March, so spring will begin to appear in 6 weeks in this northerly tundra.

PS- Thank you for all this knowledge floating around. I've definitely spent ours reading posts about cars that I don't even own.

[stevembraun]

Sorry, I forgot to add, the car has 141000 miles on it.

[abscate]

steve - I assume s/he replaced the oil pressure sensor too? If the oil pressure light is on, but the oil pressure tests ok, isn't that a pretty good diagnosis?

If the sensor was bad, would it be on right away, instead of waiting ~15 miles.

These units can fail in a 'complex' way, so I would say the answer to that is "No"

[stevembraun]

Just wanted to close the loop on this question. I got my car back after the weekend. The problem was the mechanic hadn't changed my oil filter (why not, I'm not certain), and he believed that it was so full of crap that it was restricting the flow of oil. Whether or not that was true, he changed the filter and the light stopped coming on. As always, start with the simple solution and work your way to the most complex.

[abscate]

Life is good. Carry on...

[traxcavator]

I had a similar problem on a 2000 V70XC. Write up is here: https://www.matthewsvolvosite.com/forums ... 26#p347726