Ok, here's the deal my 97 540i with 160K has indicated that it has lost oil pressure 3 times in the last year. It happens after a quick throttle blip (rpm up to about 3 or 4k), warm engine. The first time I shut down, check oil, level good, restart still no pressure indication (no lifter racket though like you would think with no oil pressure). Dealer diagnosed next day as bad pressure switch. No problems for several months. Then happened again about 4 weeks ago, same way, I left car overnight in parking lot (afraid to move) went back with flatbed and just to see, started car. Oil pressure ok. Took home on flatbed and replaced pressure switch and dropped lower oil pan to make sure oil pump bolts tight. All three bolts in place and tight. 2 days ago same thing happens after another blip on throttle. I'm thinking, can't be another switch. In between incidents there have been plenty of full throttle excursions to the redline when going places. But those didn't result in loss of pressure indication. Anyone with any suggestions? Maybe an overpressure bypass that is lifting and not reseating (engineer speculation). Thanks for reading the long post and for any suggestions.
You shuold probably replace the oil pump. They are so easy to replace that it would be your best bet. Since you know what you are looking at, you have remembered to tension the pump properly, correct?
I would not rule out the switch. Those things are notoriously cheap. I do not know why, after literally decades, BMW has never specified a durable replacement, but the truth is, they haven't. They are not unique in this regard. I have found the same in my experiences with Audi and Toyota, as well. The simple fact of the matter is, even if you replaced the thing only a month ago, the most likely problem is the switch. You sound like the kind of guy who can test the oil pressure, so do it. Once you have verified that you have good pressure, you'll know for sure.
Of course you should hook up a gauge first. I am brain drained today. I only suggested it from having seen weak oil pumps intermittently on that vintage BMW (not very common, though.)
Thanks for the replies, I don't have a gauge at the moment, but will get one. Will most big auto parts chains have the necessary fittings to go where the current pressure switch is? Also the chain tension appeared a little loose but didn't seem to be in danger of coming off the sprocket. The bentley manual seemed a little vague on how to adjust it so I didn't mess with it. Maybe I'm not a savvy as you gave me credit for. I'm not a bad wrench wielder but always have more to learn. I'll try the gauge and go from there. Thanks again.
I posted this a long time ago. Never followed up. Turned out there was a broken piece in the oil filter housing internals that was sporadically blocking the return. Local independent mechanic found it and voila, no more problem.
