0W-40 OK Follow Up

I went ahead and put the 0W-40 synthetic oil into my 1995 Grand Am four cylinder. As expected the hot idle pressure went up. It went from about 12 PSI to
about 20 PSI. So I achieved my goal. The problem is that all other times the pressure gage is pegged past 80 PSI. A mechanical gage shows the pressure about 120 PSI and the needle shakes widely.
A responder to my original post suggested that the cold maximum pressure of 80 PSI seemed a bit high. He was onto something. I am guessing that the pressure relief valve is sticking. I wonder if this was causing the low (12 PSI) at hot idle with the 5-30 oil. Looking at the manual, it seems like a time consuming job to get to the pressure relief valve and that might not be the problem. The car is in good shape and I want to make it last a lot longer.
I don't know what to do. Any suggestions?
Thanks, Scott
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My suggestion would be to go back to the oil you were using, which I believe was the oil recommended by the manufacturer. Idle pressure was apparently within spec when the engine was using that oil. I'm not sure which problem you solved by switching to another oil. But the engine is now apparently pegging the oil pressure gauge.
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John S. wrote:

I agree with re-installing the original spec oil, but a good quality. Try the Castrol(?) blend for high mileage engines. The higher the oil viscosity, the higher the resistance to flow. 12 psi at idle is fine, as long as you have adequate pressure (30-50) around 2000 rpm. Your gauge is registering the 'backup' in the system. If you have a worn bearing, the oil will literally be spraying out of the clearance, somewhere in the crankcase. Some situations like this, can overload the oil rings on a piston and you'll start burning it. 100 psi can blow through an old gasket easily. So, start looking for drips..
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Don't waste time and money fooling around with changing oil spec. You have a problem and it is NOT the oil. DO NOT DRIVE IT THIS WAY. Get the oil pressure regulator checked and repaired YESTERDAY like.
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Last time I saw something like that was on a GM too. I asked my 'friend', who does his 'own' work, when was the last time he changed his oil filter and he asked me 'where' that was....
His pressure was either real low or pinned, just like yours.
Having the wrong oil pressure and/or running the wrong oil isn't really good for the life of the engine, if it is the valve failing, it should be fixed before...
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip Photos: http://mikeromainjeeptrips.shutterfly.com
Scott Buchanan wrote:

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Scott Buchanan wrote:

I think there may be something missing here. The viscosity ratings for oil are not all that precise in their meaning. In theory when the temperature is cold 10w30 and 10w40 are supposed to be the same viscosity, but anyone who has poured 10w30 and 10w40 from a bottle when the temperature is around 0F knows that 10w40 is a lot thicker.     In theory the 0w40 should be thinner than 5w30 when cold. But that depends on how cold is cold. What's missing here is - you haven't said how cold it is where you are.


Where are you measuring the pressure? Where is the oil filter and pressure valve in relation to where you are measuring pressure?
-jim

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On Thu, 6 Dec 2007 21:06:26 -0300, "Scott Buchanan"

If the PR valve is stuck closed it will not cause low oil pressure at idle. It WILL cause excessive pressure at speed, and is just about the only thing that CAN cause it using that oil. I think there is an external plug to get the regulator valve out, but I'm not that familiar with your engine. You definitely need to get the regulator(pressure relief valve) checked and repaired before driving it...
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