91 5.2L with 146xxx KM's

The gauge really fluctuates when warm...ill be at a red light and it will go down real low, sometimes to the point of were the low oil light will flicker on and off a bit. But once i get the rpm's up it will go back up, usually a little past half on the gauge. When the engine is cold it stays pretty much in the middle and doesnt move. What are some possibilities? If i take it to a shop to get a oil pressure test done on it, that shouldnt take them more than a hour?

 

It sounds like the oil pressure sender unit (oil pressure switch at autozone) is giving up on you. I just changed mine in my '95, same symptoms as you.

 

cheap fix? no specialty tools needed?

 

I had the same problem with my 94 5.2l, I changed to 10W40 oil and added some lucas in there with it and haven't had a problem since, other than one time when I went a little too long between oil changes. This is something cheap and easy to try...

 

The only specialty tool you will need is a socket made for sending units. Make sure you get one that will hold the unit in while you position it, and whatever you do, don't take a wrench to it until after you've caught a couple of threads, cause where that is you don't want to be having to re-tap the hole if you strip it.
I had the same problem on my '95. I replaced the sending unit first and it went away for a while then it came back. I had the sending unit tested and it was good. This time it was my oil pump. I can't complain, the truck has over 187K on it, so replacing the oil pump didn't bother me. The manual labor involved to do the pump on the other hand was a pain. Good luck!