Johnv

So this engines oil pressure was fine until the oil pump was replaced ?
or was a freshly built engine that your having issues with ?

Could be the barbell (oil gallery plug at back of block)
Could be cam bearings, I just had one walk out of a rebuilt engine causing low oil pressure.
could be missing the oil gallery core plugs if engine has been rebuilt.

or could be excessive bearing clearence, did your friend mic or plastigauge the big ends and mains ?

Oil pump pickup oring is the most commen cause.
maybe a stuck pump relief valve ?

98RedBird

iTrader: (77)

Did he plastigage the mains/rods? Or pull the cam and mic the cam bearings? That's the only way you're going to somewhat accurately measure the clearance on the bearings with everything still in the car.

As long as the pump and O-ring check out okay then the problem is either in the galley's (a leak, possibly the barbell plug was mistakenly not installed or either the front or rear covers are leaking at the gasket that directs the oil 180 degrees down the lifter galley's.), or the problem is in the bearing clearances.

And good parts don't mean dick if it was poorly machined/built.

slayerized6

iTrader: (12)

To the OP, I literally have the same exact problem as you.

I also have a 1998 Trans Am. Around 3/4 weeks ago, my oil pressure started dipping down into the 20's at warm idle and would be around 30psi cruising once warmed up. My pressure would be ~40psi at start up, but it went downhill once warmed up. Sometimes the pressure will fluctuate while cruising at a steady speed. At 1800 rpms in 4th gear, it would fluctuate back and forth multiple times between 30psi and 40psi within a matter of seconds.

I got the idea from a different forum that the problem could be a stuck open pressure relief valve. I went ahead and got the oil pump replaced. I had a thunder racing ported oil pump installed by a local shop. Even after the new oil pump, I still had the same problem. But on a good note, I have a little extra pressure from the new pump.

My car has been running fine. No new noises, no new vibrations, no ticks, etc.

According to All data, my engine does put out enough pressure to met minimum requirements. However I am still a bit worried that there could be a bigger underlying problem Im unaware of


Oil Pressure (Minimum-Hot):
At 1,000 rpm 41 kPa (6 psig)
At 2,000 rpm 124 kPa (18 psig)
At 4,000 rpm 165 kPa (24 psig)

98RedBird

iTrader: (77)

Swap your pump and sending unit. I had a 98 T/A that did the exact same thing. Swapped the pump and sending unit just to cover both bases and she was up to 60 at cold idle and 40-45 cruising, 35-40 hot idle.

slayerized6

iTrader: (12)

i understand your point by covering the bases, but why would my OPSU crap out only after my engine warms up? Ill probably end up swapping either way, but i just dont understand why the sensor will give false readings only when the engine warms up. Now i just gotta wait until a nice day comes by to pull the manifold and replace the sensor

98RedBird

iTrader: (77)

Oil pressure sending units can and do act up and go out on these cars. It's not at all uncommon.

slayerized6

iTrader: (12)

i just did some research on OPSU's for ls1's. the 98 has a different sensor than 99+ units. me and the OP both have 98's so i guess thats a common denominator. i already changed the sensor in mar/april '09 when i did my intake. Maybe this time ill be able to get the intake off within 30-45 min .

btw, i meant to say my oil pressure is above 40psi at cold idle. I get 55-60psi at cold idle with my new, ported oil pump. Oil pressure starts to dip right when my engine reaches 130*

ill be ordering a new OPSU from the ws6store later this night.

Black LS1 T/A

Slayerized6 ... your problem seems EXACTLY like mine.

The only thing about the OPSU ... isn't that easily determined by checking the true pressure with a separate, external gauge? Or are you guys saying you can TRULY have low oil pressure because of some issue with the OPSU?

This part is amazing:

That is just like mine was, when completely hot and driving it. When I hooked an external gauge to it, it was a couple or three psi higher. But, those numbers are almost "psi for psi" what my stock gauge told me. Since replacing the oil pump, idling it in the garage, it gets to about 10 psi hot. If I rev it, the pressure jumps up to about 20 or so ... but, I'm only rev'ing it about 1000 or so rpms with a pat of the foot.

jeffman127

iTrader: (2)

I am having the same problem. I just installed a slp unit into my 98 camaro. Cold idle is great and after warmup drops down to under 20psi. I replaced the oil pressure switch (without removing manifold) and still has same pressure. All signs point to o-ring. I will be replacing the o-ring by dropping the oil pan this time. That way I can make sure the o-ring seats nicely.

stangbeaterz28

iTrader: (6)

I had the same problem, sometimes at idle mine would even DROP TO NOTHING at the gauge. I had ZERO noise with a ms3 cam and could crank it all the way up to the rev limiter with no issue. Hooked a manual guage to the Oil pressure SU just to verify the gauge and it was still reading almost nothing at idle, i know i paid careful attention to the o-ring...

Upon tearing back down i realized the 4 bolts holding the oil pump to the block had backed off, i must have forgot to lock tight them or didnt tighten properly and the gap between the two machined surfaces allowed oil to fall back into the pan after passing through the pump.

Again, i had no noise even with the big cam and stock lifters, the car drove fine...

Black LS1 T/A

Hmmm ... remember I said the car has sat up for about 2 1/2 to 3 years?

The weekend I grabbed some STP oil treament and ran that for a while at hot idle and rev'ing.

Then, today, I grabbed the best filter I know of (WIX filter, to me ... but the one that's an inch longer, for a 6.0 block) and some Castrol 20w50 (I've always run no heavier than 10w40 the whole time I had this car.

When I drained the oil, I couldn't believe how sludgy it looked and felt. I turned the engine over a few times without letting it start up, just to build some pressure. Then, when I saw some pressure build again, I let it run.

Solid 40 PSI at cold idle (about 1300 rpms). But instead of drifting downward, it stayed there until it warmed up and the idle dropped down to 900.

OK ... that's about 3 psi higher than earlier. But .. let it warm up.

After warming up, min was 30 psi. I rev it once ...went to about 45, then back down. I let it idle, rev, idle, rev. Then I rev'd to about 2500 (went to about 45-50 psi), in that way that when it bounces off idle it would almost cut off. Oil pressure dipped to 10, then steadied up to about 22 or 23 psi. That's the minimum at idle now. If I rev, I can get it up over 40 - 50 at around 2500 to 3000 rpm.

Tell me what you think?

Black LS1 T/A

And, I wonder if there is more old oil in there that I will need to drain yet again, later? Could it be that simple? Or did the weight of the oil and/or filter make all the difference.

Also, remember this low dip in oil pressure was rather sudden, after leaving the track one evening. This was not gradual.

ae13291

iTrader: (8)

you guys really should have used the oil pump pick up tube girdle that goes over the tube and uses the 2 threaded bolts rather then 1 bolt. i did that and have not had a problem

stangbeaterz28

iTrader: (6)

when i first started mine and drove it, i had EXCELLENT oil pressure. then like you, suddenly it was almost nothing. When i would rev it, i would get decent pressure... again like you it bounced all around. The pump was getting enough oil even with the gap between mating surfaces to keep the motor alive for about 1,200 miles. Then a stock rod bolt broke\

Then when doing the tear down, obviously saw the pump had a 1/16-1/8" of clearance to the motor, i think the only thing that kept it from coming completely off was the timing cover.

jeffman127

iTrader: (2)

Where did you get that? I have never seen that before.

Black LS1 T/A

Well, nix that about the oil being whack. My mechanic friend said when he drained the oil it as like new. It should have been ... I had just changed it, even though it sat a long time after that.

We agree the wierd consistency I was seeing in the oil I put in when I got the car back was the STP Oil Treatment that I had just added to it the weekend. It was kinda snotty feeling.

The increase in oil pressure is evidently only due to upping it to the 20w50 and perhaps the better flowing WIX filter.

01ssreda4

iTrader: (96)

I think you should run whatever oil is recommended for the car/climate.

ae13291

iTrader: (8)

http://www.brphotrods.com/Girdle.html

this is the site that sells them but i was able to make my own out of my dads mill machine

stangbeaterz28

iTrader: (6)

i would pull the timing cover and check it out man.

Black LS1 T/A

I will do more than that. I'm gonna pull some more money together and pull the engine with a mind to go into it. So, I will need a rebuild kit. I'll take everything back off the front of the engine before I pull it and check that. I started my portion of the work at double-pinning the crank (the single-pin had been sheered off) for the Super Damper and replacing the timing cover on outward. The pump was definitely on tight and everything at that point was buttoned up.

As I get back to the Timing Cover, I'll look at it. But, I was just there last week. This guy is thorough. He described to me how he followed instructions for putting the pump in ... how he knows about taking care with the o-ring. There must be something else wrong. But, I'll check it, anyway.

I dont know how long it will be before I can get to it (removing the engine), but I will come back and post so the thread is properly closed out ... I won't leave everybody hanging. I hate it when people don't post final solutions to a thread they started.