My '87 s10 has a whole slew of problems, but honestly I'm not sure where to put them in the forums. But this one is definitely "non-specific". Basically, on a hot day, or after a lot of driving, my oil pressure goes very screwy. It dips a bit, shoots back up, drops like a stone, etc etc. Now, I'm assuming this is a problem with the pump? Or is there a known problem with the gauge?

 

is it instantly popping around? or is it like a sliding raise and fall? Warm,these engines
(at least i know the 4.3) can idle at 20 psi. Which is normal. Cold 35-75. As soon as you touch the gas it'll raise back up to 40-45 ish.

 

a 4.3 can idle safely around 5psi, lol. Oil pressure rises as rpms go up, and drop when it goes down. Low oil pressure can be from worn crank and rod bearings, weak oil pump and the such. Unless it's staying at 0 like dead ZERO and goes above 20-30 while driving normally your fine. Also cold = high pressure and warm = low pressure. It's like heating up syrup

 

You need to connect a mechanical oil pressure gauge to the sending unit to verify if the dash gauge is reading correctly or not. If it is, then you most likely have a bad oil pump.

 

I dont think its a problem with the guage its a worn engine with a weak oil pump thats causing this to happen.Its quite normal for an engine with high milege to do this.
My truck has a 4.3 with about a 190k miles.It will start up cold at 60psi.As the engine warms the presure drops to 35 psi at idle,when I step on the gas it will go up to 50psi.

 

OK, I'll start making note of the actual numbers, but it does sound like a weak pump. Its an old car, makes sense that things would start to wear out. I'll look into fixing that. Is the oil pump essentially self contained except for obviously the lines? What I mean is, is this a mechanic job, or a me job?

 

Oh and I've got the v6

 

there are no lines on your oil pump..... Here is a picture.
if you were to do it, which you can so long as you pay attention, you have two options, pull the motor out, or try and do it with the motor in. you have to take the oil pan off the bottom of the engine. that is basically step one. thats why i would say to pull the motor out, its more work, but it makes changing an oil pump easier.
so if you pull the motor,
step 1. put motor on engine stand, drain oil, then flip over SLOWLY so you are looking at the bottom.
step 2. remove oil pan
step 3. remove oil pump being careful not to drop the oil pump shaft that is connected to it.
step 4. install new oil pump, i believe the torque spec is 35 or 50 ft-lb for the bolt, and pump shaft with new collar so it wont fall off. you should replace the oil pump shaft collar as they are only like 2 dollars and is "cheap insurance". its the little white thing in the upper right hand portion of the picture.
step 5. scrape off old pan gasket and install new one being sure to put some gasket maker in the corners and front and rear so you dont have leaks!
step 6. put pan back on and reinstall engine.

if you leave the motor in the truck:
step 1. do everything that you can to get the motor as high as you can, which is going to entail undoing motor mounts and possibly the trans.
step 2. realize you just did about 85-90% of the work it would take to pull the motor.
step 3. pull the motor out anyway.
step 4. see step one through step six above.

i only say this because i dont think that you can get the oil pan off the engine with it still in there seeing as i had and 89 and i couldnt because the cross member isnt removable and there isnt enough room.

 

If you end up pulling the motor to change the pump I would change the main bearings also.