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I have an 82 Z28 with a 355 that has approx.
9-10K on rebuild. My problem is that when the engine is cold, I have 50-60 psi of oil presure, but when the engine is warm, I only have 5-10 psi. There is a little bit of smoke coming out of the tail pipes because the I have had a hard time getting the rings to seal. But I have been told that this is not the problem with my oil presure.
Please help!
 

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seems a little low, but a general rule of thumb is 10psi per 1000rpm. does this sound like what you have? has this been a recent, sudden problem you've noticed? if not you're probably ok, just keep an eye on things.
 

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what oil are you running, please dont tell me 0 or 5w anything... if so theres your issue, thicken the oil up a bit, oil thins and loses viscosity with heat. so thus the drop in pressure,However , if your pressure goes up as the RPM's do , dont sweat it. its fine. my good friends 98 Vette is the same way, 15lbs at idle, then it goes up

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[This message has been edited by Chris Edwards (edited 02-20-2002).]
 

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What's Wrong with 5w Oil?
I ran 5w oil in my Trans Am up until the engine blew (no joke intended).
I'm wondering if I should use a heavier oil?
 

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5w 30 has the properties of 30 wt at normal temps but takes on the properties of thinner oil when it's cold out. 0w 30 or 5w 30 should not be any different than straight 30 wt when the engine gets warm.

Check your gauge and if it's accurate talk to the engin builder and find out what clearences were used in your lower end. If they are on the loose side a 15w 40 or 15w 50 might show better warm idle pressure.

I should have asked this first, did this just start or has it done it since the engine was new?

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"The '69, the '96 & the club"
 

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I agree with Dennis, I use 5w-30 in all my cars, 100% synthetic in fact. The thermal stability at all temps is safer too.
I think something else would be involved in that pressure issue other than the oil at this point. The guage, tolerences, etc.
But if it just 'started' doing that, dont push the engine until you get answers from your engine man.


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My brand new 454 has 15 lbs hot pressure at idle, but climbs to 40 lbs @ cruising speed.
This is with a el-cheapo guage so who knows.
As long as you're building pressure with
rpm increase you should be o.k.
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by mls48341:
My brand new 454 has 15 lbs hot pressure at idle, but climbs to 40 lbs @ cruising speed.
This is with a el-cheapo guage so who knows.
As long as you're building pressure with
rpm increase you should be o.k.
<HR></BLOCKQUOTE>

Well, time to tell my story again... 2 yrs ago, fresh 383, nice parts runs well but has about 5psi at idle warm. Engine builder doesn't like it so out comes the mill. Lower end gets looked at and a new oil pump goes in... Mill goes back in the car... Same 5 psi warm but climbs 10 psi per thou rpm. Builder shakes his head but says run it, if it breaks he'll fix it. I switch to Kendall 50wt and see about 7psi warm idle. We talk about the slight increase and I learn it's because he set the clearences just a freckle to the loose end of spec's...

I drive the car all summer, maybe 3000 miles and builder and I just keep shaking our heads. Every time we get together it's could it be.... The next summer it's driven about the same our longest trip (Hot Aug Night in Reno) came and went and I changed the oil on returning. Well I started to notice that when warm the pressure was not what it was!
Still about the same at idle but the longer the drive it seemed to fall off some. Straight to the builder and out comes the mill again. Now the mains are all copper and worn badly, rods look ok.

Final diagnoses: Casting flaw in the block that manifisted into an internal oil leak causing the low pressure at warm idle. The 4 nights of cruising at HAN (idle speeds for hrs on end) is what we suspect killed the bearings...

What I am trying to say with all this is if your always rev'd and rolling there may never be a problem. Just be aware of what extended idling can do...

If your clearences are a bit on the loose side run a heaver oil and you may see things improve.

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...Dennis
"The '69, the '96 & the club"
 

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DJD,
Good story, good point about checking clearances.
Did the guy honor his word and set you up
with a good motor?
Being the owner of a machine shop and having
assembled the engine myself, clearances are correct on mine but food for thought.
 
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I had the same trouble with the oil pressure. After making sure the oil gauge was ok, I put new rod/main bearings and a new oil pump and now I have 60 psi cold and 40 psi hot.
 
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