i have a 1988 2.4L 185,000+ miles chevy s10 pu. the check gauges light has been coming on for some time. the gauge bounces up and down a lot. but settles to 20psi at driving speeds. there is no tapping or noises from the engine and has good power and oil. what should i have check
i would try replacing the oil pressure sending unit. It is relatively cheap and easy to do. And if nothing else it will either confirm or rule out that possibility.
Sounds like a typical aging GM engine. At this age and mileage, this is very common on pretty much any GM engine. It does mean the engine is well worn, but does not necessarily mean it will fail any time soon. I have owned many GMs that do this, and I have known of others who have driven them like that for years and accumulated tens of thousands of additional miles with the oil pressure gauge acting like a tachometer the whole time. What I do when I have a GM vehicle that does that is keep an eye on the oil level and drive on. If it starts using oil excessively or making noise, then you have cause for concern.
What does the volt meter indicate? If the indicated voltage is under 13 check the gauges ground wire near the parking brake.
You should be running higher oil pressure than 20 psi at highway speeds. The oil pressure dropped to below 10 psi on my '88 Escort back in the winter. The problem I found was the pick up screen on the oil pump was clogged. After removing the oil pan and cleaning the screen the oil pressure returned to about 50 psi at 55 mph. This is on an engine with 517+K miles.
A clogged oil filter or one that has damage can also cause low oil pressure.