oil pressure GM 5.7

[mikebrown2008]

I bought a 99 tahoe with 180k miles. On the test drive the oil pressure was around 25psi idle and 45 at speed. After driving it home for about an hour at highway speeds the oil pressure was 25 psi at speed and around 5 psi at idle. Is this normal for this engine. Should I change the oil to a 20w50. For what its worth it runs like a top and the engine is very quiet.

 

[The_Jeff]

Someone is going to chime in and say put a real gauge on it.

Does this also have an oil idiot light or does it ding and say "check gauges"? 4 psi is usually the idiot light threshold.

 

[stxonall8]

Test the pressures with a mechanicalgauge to verify this first.

 

[NHGUY]

Replace the sender,maybe its worn.

 

[beast3300]

I would suggest using an external oil pressure gauge to verify. GM or anybody else's dash gauges are not real accurate. I have seen this low pressure condition on high mileage 350s.

 

[stxonall8]

Change the oil out with some fresh 10w30 as well to rule out poor quality or worn out oil.

 

[aquariuscsm]

Aren`t those oil pressure guages simply "idiot lights" via needle? I`ve heard that they basically read on/off and are not pressure sensitive.

 

[Brons2]

Originally Posted By: aquariuscsm
Aren`t those oil pressure guages simply "idiot lights" via needle? I`ve heard that they basically read on/off and are not pressure sensitive.


That's on Fords. The GM gauges actually move.

 

[dparm]

20w50? I doubt it needs something that thick.

 

[aquariuscsm]

Originally Posted By: stxonall8
Change the oil out with some fresh 10w30 as well to rule out poor quality or worn out oil.


^^Do this

 

[bullwinkle]

I ran 20W50 in my '94 high mileage (215K at the time) 350 and it didn't hurt it any, still started fine cold. Have since switched it to Nextgen Maxlife 10W30, hot idle oil pressure is a little low at 10-15 PSI but no lights or warnings. 5W30 actually burns off quicker in it, Maxlife has been doing 1500-1700 miles per quart.

 

[caravanmike]

i believe the 5.7L is suppose to be at 18psi at hot idle. i vote for a fresh 10w30 oil change to rule out sheared fuel contaminated oil from previous owner. and also vote for mechanical oil pressure guage verification.

i also have seen some (including my brother) run 20w-50 in a sbc with no issue, especially with you being in tx

 

[tightwad]

Don't know about the 1999's, but the later models have had big problems with bad sending units. Recently was on a trip with a friend in his 2007 Yukon, and in the middle of nowhere a beeper started going off. DIC said low oil pressure. He knows nothing about cars. We pulled over and checked the oil, and I knew it had oil pressure because the lifters weren't rattling. We made the next 50 miles into town. The next morning, the service writer at the GMC dealer goes "oh, here we go again, another sending unit".

 

[dave1251]

To maintain the proper oil pressure if I had to use 20W-50 I would start saving to have the engine rebuilt or to buy a new one. But that being said you could get another 100K+ of service out of the engine.

 

[OVERKILL]

Originally Posted By: dave1251
To maintain the proper oil pressure if I had to use 20W-50 I would start saving to have the engine rebuilt or to buy a new one. But that being said you could get another 100K+ of service out of the engine.


This. 5psi (verified with a mechanical gauge) with the spec'd oil weight is really freakin' low and indicates a whole lot of bearing wear. It is an indication of rebuild time.

 

[mikebrown2008]

Its a truck I bought for 3000 cash. If I can get 30000 more miles out of it I will be happy with that. That being said I think Im gonna go the 20w50 route and see what happens.

 

[mikebrown2008]

Would Mobil 1 15w50 work better in this engine than a conventional 20w50.

 

[dave1251]

First you stated that you do not want a engine rebuild and you would be happy with 3K more miles of use. Now you are asking if M-1 would be better for engine protection. What is not right with this picture?

 

[Jocephus]

my vote goes for trying new 10w30 in a good conventional before you start throwing in much thicker oils like 20w-50.

 

[A_Harman]

Verify the reading with a mechanical gauge. If it really is that low, you can try the 20w50 thing, but it might not get you to safe oil pressures. "Safe" meaning nothing below 12-15 psi at idle.