I changed my oil for the first time since buying my car yesterday. The oil was in decent shape, black, but no chunks or anything. I put in mobil 1 5w30 with a fram filter. After the change the car was acting like it always has... 30 pounds of pressure at idle, 60+ under throttle. Then late last night, it noticed it would maintain 30 pounds at idle, and stay at 30 pounds under throttle. It's still like this, and as I drive it the oil pressure tends to steadily drop. This afternoon it was running for a while at around 15 psi consistently . No signs of oil under the car, in the engine bay, or in the coolant overflow reservoir. The dipstick looks like clean mobil 1, but I'm about 1/3" overfilled. I've heard it's either the pump or the sensor. Any ideas guys?

 

try a mechanical gauge and see what you really have

 

yeah our third gen gauges seem to like to be a little looney. My oil pressure gauge went nuts just a few weeks ago. Now its fine after its temper tantrum.:lala:

 

Someone suggested I put a guage on the sender unit for the oil pressure guage to see my actual pressure. Where is this sending unit located?

 

It could be the mobil one, before I changed to it my car would have 50-60 psi all the time (by the factory gauge). Then when I changed over it goes from 60 when cold at idle, or over about 1500 rpms to 30 at idle when warmed up.

 

i was thinking the moblil one also, synthetics are diffrent than regular oils, you may also be cleaning junk off you block and plugging up you pickup screen. this would be a far shot but i have heard of it before with synth oils and a dirty engine.

 

Well the wierd thing is that it was normal immediately after the swap to mobil 1. Other than that it's exactly my story. You aren't worried at all about this??

 

id replace your sending unit... i had the same thing happen to me eventualy it went all the way to zero and wouldnt climb at all so i shut the car off at my friends and t sat there for 3 dyas caus ei thought the oil pump was bad and i was told to replace the sender wich is like 12 bucks and i did and it pegs 60 again

also instead of 5w30 i think u should be running like 10w30/40

i thought 5w30 was for winter cause it is a bit thinner

 

You are correct. I won't reach another 5k miles until winter is over, so this is my winter oil. Where is the sending unit located?

 

The sending unit is either located off of a T coming off the rear china wall, behind the distributor. Looks kind of like a small bell with a wire or 2 coming off the top. The other place is down on the block itself, just above the oil filter.

depending on if you've changed things like me, either look for a 1 wire sender or a 3 wire combination "sender/switch." Best thing to do is to bring it in with you into the parts store to eliminate any confusion.

 

If the mechanical gauge reads the same once you hook it up, I'd bet it's the pickup getting clogged. I made the mistake of running too long with a clogged pickup thinking it was the sender being screwy. One rev too high and now it sounds like I bent a pushrod.

 

Where is the pickup located? Maybe I could just take a look at that if it's anywhere near the oil pump or sender.

 

oil pickup requires removal of the oil pan. And you can't just lower the pan as it's all the way at the bottom.

 

My plan is to get the car on stands, drain the oil, remove the pan, if the pickup is clogged, clean it, bolt the pan back up, put in a new filter and oil (and take a look at the sender while the filter is off). If the pickup looks good I'll replace the sender. If that doesn't work, I'll look into a mechanical oil guage and replacing the oil pump.

EDIT: Hmm isn't there that crossmember down there under the oil pan?

 

Yessir

Plan on removing cap/rotor, seperating the motor mounts, and then jacking the motor up a few inches. Not quite so easy on these cars as it is on others. Assuming everything isn't rusted solid, should only be a couple hour job still.

 

Oil pickups are cheap enough to replace. Unless you don't want to go through setting the depth and all that.

 

I finally got around to take a swing at this oil pressure problem. I heard 5w30 was too loose for an SBC so I bought some mobil 1 10w30 and an acdelco filter to replace the fram I used at first. I decided to wait on dropping the oil pan to fix this issue, so I drained the synthetic 5w30, replaced the pressure guage sender, and put in some dinosludge 10w40 leaving the old fram on to see if it worked or not. Well guess what?!?! Now my pressure is disgustingly HIGH. Idle hangs around 50-60 (or at least the guage says so), slowly increasing under throttle. Any input guys??

 

I wonder if the fram filters cause problems....mine has one on it and it does exactly the same thing.....had PLENTY of oil pressure, now, stays at about 25 when cold, when hot, drops to literally nothing....

I'm hookin up the manual pressure guage tonight,.....I hope its ok!!

 

If that's what the oil pressure gauge confirms, I'd look towards loose bearing clearances.

 

I can't say enough good things about aftermarket mechanical gauges. My stock gauge showed no more than 40psi now matter what. With a mechanical autometer gauge it shows 30psi at idle after its real warm. 60-70 under hard throttle.

I would suggest getting a mechanical gauge anyways. Much better.

And a mechanical gauge will cost you about as much as that mobil 1 synthetic you just drained out. Possibly for now reason.

 

As long as we're on the subject of oil press gauges, I have thought of putting a mechanical gauge into the hole at the front of the block right ahead of the intake and slightly off to the passenger side. Just for a quick double check in case I feel like there's a reason to doubt my factory ga. It would be a very simple install, probably about 5 min.
Is it a good idea to mount a gauge there, or would the pressure reading be untrue since it's further away from the pump?

 

That's where I had to move my factory gauge sender to because it was interfering with my manifold. It's reading is exactly the same, but it takes half a second longer for it to read pressure on startup. My guess is that it's just because it's a little further from the pump If it's anything like mine was, you'll need a square drive socket to get the plug out. It was rusted in way to bad to get it out with an open end wrench.

 

welp, put a new mechanical guage in my car, hooked it up to the port behind the intake mannie...started her up...........

50 PSI OF PRESSURE!!!! WHOO HOOO!

So I know for a fact that my guage is just screwy. I also had some leaking gaskets on my valve covers....fixed thems up, no more leaks


cept that stinkin stock oil pressure sending unit.....friggin crap GM parts.

cheers!