hey guys, I recently picked up a 99 trans am with 213k on the clock. not sure if the motors ever been replaced but it doesn't use/leak a drop of anything, anyway my oil pressure seems low to me. I have 45 psi at cold start up. once warm I have like 25-28 at idle in park, bounces 20-25 in gear idle. cruising on the highway (1500-2000 rpm) I have 30-35. WOT I have 40-45. is this normal or is my oil pump getting weak?

 

Whats the ambient temp at a cold start up?

On a cold winter day I sit right at around 60 psi cold idle. Usually hovers a bit above that until the oil warms.

With a fully warm engine I'll be between 38-42 psi at idle.

Mine has 163k on the clock.

Should you be worried about it? I dunno. I've seen oil pressures all over the place in these cars. As long as it rises with the RPMs in a satisfactory manner, I wouldn't worry.

 

You are a little on the low side. Most are around 35-40 psi hot idle. With all those miles you probably have some wear and i am sure your oil pump o-ring needs to be replaced.

 

air tempature has been anywhere from 40-75 lately. doesn't really seem to change at all with air temp at cold start. been using 5-30 vavoline synthetic.

 

Huh? I've seen never heard of this problem unless the O-ring was new and not installed correctly.

This is normal for an engine with that many miles and still well within the safe range. The reason for the pressure drop is
- Oil gets thinner as it warms up
-Oil get thinner as you put running hours on it
- Parts expand as they heat up so tolerances open up as the engine comes up to running temperature
- Tolerances open up as parts wear.

GM service manual says at operating temperature minimum pressures.

6 psi @ 1000 rpm
18psi @ 2000 rpm
24psi @ 4000 rpm

anything under 6psi you will see the oil light come on and probably warning light to check guages.

 

may be a tad low. with those miles, like gagliano said, bearings prolly
have some wear on them. i know mine did when i took apart the block
@ 188k miles.

 

I'll just run it for now I suppose. If it gets to under 20 at idle I'll just yank the motor and go through it. Motor still seems to be as strong as ever and runs fine. Just wasn't too sure about the oil pressure because my 01 5.3 z71 with 240k has at least 40 psi at all times.

 

The o-ring gets square and dry rotted over time. I was surprised how brittle the one i took out of my 6.0 with 130000 miles.

 

Low normal, I wouldn't worry about it. My 98 with 174K idled about the same. My rebuilt LQ4 with a melling pump hot idles around 50 PSI.

 

I agree with gagliano about the pickup tube o-ring. They do get old, brittle, and they sort of rot. Been there, seen that, got the t-shirt.

As for the original question your oil pressure does seem a bit on the low side. With the mileage I don't suppose its too bad. Also early LS motors didn't have the greatest oil pump.

If you wanted to do preventative maintenance you could buy a new oil pump and put on a new o-ring. Or just leave it alone until its time to rebuild the motor.

 

I wouldn't worry one bit about those pressures you described, especially at that kind of mileage you have. Clearances get looser over time and oil pressure drops, doesn't necessarily mean it's a bad oil pump just means your engine is starting to wear.

I'd certainly keep an eye on them from now on to ensure they don't get any worse, but those are plenty to maintain a healthy engine. Maybe do an oil change with w40 oil next time.

 

Oil pressures are all over the place in these cars. I just replaced my factory oil pump with a Melling 10295. I get 50 PSI on a cold start, ~25 on a hot idle, and hot cruising is around 40-45psi. Some say this is too low, others say it's fine. My oil pressure rises with the RPMs, and doesn't fall during WOT.

With the stock pump I was getting a little under 40 PSI hot idle, but I was also running 0w-40, now I'm running 5w-30.

 

Sure way of knowing the o ring is getting bad is the lifters start to get louder and louder.

 

IF this happens as the result of the o-ring, does it mean that they are damaged beyond the point of 'coming back' and ever being quiet and functional again, or is it just the air making them noisy, with no permanent damage?

Also, could a leaking o-ring also cause the needle on the dash gauge to 'twitch', or flutter at full hot idle, even if the pressure is showing within the OK specs (~35-40 psi)???

 

Yes it could make the needle move around. Mine were LOUD for 85k miles until I added some TransX to swell the oring and 6 ozs of ATF to clean the lifters every oil change. Mine is quiet now and it was LOUD! But my car wasn't beat on too hard. If you beat the hell out of it with air in the oil system for too long of course things get worn. You are probably ok, these are tough engines in stock form.

 

There are 3 different Trans-X products on the shelf at Vato Zone, which one is it??

Also, wouldn't the petroleum distillates (listed as FIRST ingredient) in the Trans-X DESTROY what is left of the oil pump/pickup tube o-ring seal, instead of just swelling it (like ATP-205, and Blue Devil rear main seal additives would)?

 

I used it many times without any trouble. It certainly can't be any worse than being in acidy dirty engine oil! Walmart has it for 5 bucks, its stop leak stop slip only one I know of.

 

my car has 92k and it has the same oil pressure ranges. i tried the trans x treatment when rockin recommended it to me a few months back but i havent put enough miles on it for it to really get a chance to swell the o ring.

the trans x stuff shouldnt hurt anything. its designed to swell the rubber seals in a transmission, so it wont hurt the o ring.

 

Cold start idle is between 62-63psi, full operating temp idle is 55-56psi. Normal driving full operating temp is right at 60psi, wot at full operating temp is 65-67psi.

 

Is this for your car, and does it have an aftermarket, high(er) pressure pump on it??