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Loses oil pressure

Hi ya’ll, my 89 chev p/u, 350c/i just started to lose oil pressure after warming up, goes from high normal pres. to 0 on gauge & check eng. light comes on. has 98k, never had any eng. issues befor. thanks

98K in 20 years is suggestive of a life of short local driving. Although the mileage is low, it may be simple wear.

Oil pressure is created by the pump forcing oil through the small spaces between the wear surfaces, creating a high pressure oil barrier between them. If too much wear develops the spaces can become too big, the warm oil can flow through too easily, and the pump can have difficulty maintaining pressure at idle. Short of a teardown there’s no real way to check this. A compression check would give you a good idea of the overall condition of the engine, and I recommend one, however it isn’t a direct check of wear on the sleeve bearings or their corresponding wear surfaces.

One thing you could try is a heavier weight oil. That might help.

This Doesn’t Sound Good, But I Think I Would Get A Second Opinion.

What scares me is the fact that it reads high and then low, rather than just reading only low.

Here’s how I’d get another “opinion”. I’d remove the oil pressure switch/sender. I’d buy a mechanical oil pressure gauge ($15 - $20) and screw that in and see if you get the same results. It’s good to have one in your tool box, anyhow.

You could skip this step and just buy a new switch/sender and try that, but it looks like they cost $20 -$40.

CSA

it’s not just at idle, it loses oil pressure completely instantly after engine warms, last time I rode the last mile home & heard engine rattle, so I don’t believe it’s a guage prob. I’m gonna try to find a good mechanic that I have confidence in-not easy today.

Oops! Rattle Information Withheld . . . We Have A “Bingo!”

CSA

Yup, that “little” detail about the engine rattle clinches it.
Ask the mechanic about a Jasper rebuilt engine. This engine is almost definitely too far gone to save.

it was after oil& filter change, took test ride, 5 mi’s all is ok, then sudden total oil pressure loss, I continued home for 1/2 mi, that’s when i heard rattle(like pinging) start. It will start up just fine with plenty of oil pressure right now, but I’m scared of any more test rides. Hope I can find a compentant mech. here in st pete, Fla

Perhaps the people that did the oil change could suggest a mechanic.