Low Oil Pressure: OW-40 OK?

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1995 Grand AM four cylinder 150,000 miles. Burns about 1qt of oil in 4000 miles. No oil leaks after re-torqing cam covers.
The car runs flawlessly. The oil pressure goes up to 80 PSI when cold but
drops off to about 12 when hot at idle with the specified 5W-30 oil. The in dash gage was verified with a high quality mechanical gage.
I am thinking about using synthetic 0W-40 oil to increase the oil pressure at idle.
Is this going to cause any problems?
The 80 PSI seems a little high. What should the pressure relief valve be at?
Thanks, Scott
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Yes. 0W-40 is a thinner oil which will lower your oil pressure. You want to use a thicker oil like 10W-30 or 20W-50.

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Mike wrote:

No, it isn't. However, my might want to switch over to mineral oil, synthetics tend to be a bit thinner.

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Incorrect. The cold oil pressure is high. The 0 weight is lighter than the 5, so it may reduce the already high cold start oil pressure. The 40 weight is thicker than the 30, so at hot idle the oil pressure may improve over the current 12 (which, in itself, is NOT a problem anyway).

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Not at all. 100 psi might be getting a tad high, but 80 is just fine.
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Mike wrote:

I'd say his oil pressure numbers are just WONDERFUL as-is. Why change anything? 12 PSI at idle is about 3 times the bare minimum requirement (4-5 PSI). 80 at the high end is just fine also.
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Mike wrote:

This is a misunderstanding. A 0W-40 oil will be thicker at operating temperatures than a 10W-30. The upper number references viscosity when hot, the lower number refers to pumpability when very cold.
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0W-40 is a thinner oil which will lower your oil pressure. You want to use a thicker oil like 10W-30 or 20W-50. -------- Mike.
This is a misunderstanding. A 0W-40 oil will be thicker at operating temperatures than a 10W-30. The upper number references viscosity when hot, the lower number refers to pumpability when very cold. --------------- John Horner.
What is the difference between pumpability and viscosity? --- Rodan.
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pumpability. Viscosity is basically thickness.
the number before the W is the cold viscosity - measured at 0F IIRC. Might be colder than that. The number after the w is the hot viscosity. Wide viscosity range oils have had a bad rap for loosing viscosity when hot after prolonged use.(due to polymer shear) but unless you are running extended drain intervals(which I do not advocate) ther is nothing wrong with a quality 10W40 oil.
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On Wed, 28 Nov 2007 09:12:02 -0300, "Scott Buchanan"

That said, 0W40 synthetic is a perfectly legitimate replacement for 5W30. I think you are trying to solve a non-existant problem, but your "solution" won't hurt anything.
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Good response. I guess that I should have asked if it is a problem. I just don't like to see the needle at the red mark. Especially when I am stuck in traffic at idle for extended periods of time. I was thinking that if the pressure was higher the bearings would get more oil and would last longer. Thanks.
<clare at snyder.on.ca> wrote in message wrote:

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Are you sure it's supposed to be at the red mark at 12 PSI? You may have a sending unit that is reading a little low. --scott
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I don't know about supposed to. The needle sits right on the top of the red mark which is below about 10-12 PSI. I checked the accuracy of the dash gage with a good mechanical gage so I trust what I am seeing.
The newer cars that I have seen don't have oil pressure gages. I am guessing that this is the reason why. People worry about "Low" oil pressure when there is no need to. I guess that the dealers get a lot of warranty claims because of "Low" oil pressure when the oil is hot.
My 1993 Grand Prix has what looks like a oil pressure gage but it is really not. It will drop all the way down when first turning the key on then move about 3/4 of the way up when running and never moves.
What should be the minim oil pressure be and is it known that it does not lead to accelerated wear?
Thanks
wrote:

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10psi per 1k rpm is a good rule of thumb as far as rules of thumb go.
Steve B.
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Scott Buchanan wrote:

The unofficial rule of thumb I've heard is 10psi per 1000 rpm. However, the manual always trumps that. I've seen as low as 35psi max for a 70's V8 as being considered normal.
10-12 psi at hot idle in drive isn't probably a problem for a high mileage car... but you can run something a bit thicker - again, check the owner's manual. For my cars, it's usually 5w30 recommended, but you can run 10w30, 10w40 in hot weather, and IIRC my Subaru even allows 20W50 (if you live in Texas.)
So, if you're running 5w30 and you're reading low pressure, if it was my car, I'd start by switching to a 10w30 or a 10w40 and see what the gauge reads after, but where I live it's 0w30 in the winter...
Ray
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On Fri, 30 Nov 2007 04:38:49 GMT, news

ontario summers.
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I wouldn't use oil that thick in Death Valley in August, let alone in Ontario.
But then the OP doesn't have a Toyota, either.
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I've used it in the summer on every vehicle I have owned since about 1973, except for my current Mystique and TranSport where I use 10W40. I generally put about 200,000 miles on an engine. Never had a lubrication related engine failure. Closest would be valve guide failure on 3.0 Mitsu - and they would fail regardless what oil you used. Chevy's and Pintos/mustangs (2300cc) back in the '80s that ate camshafts did NOT eat them with 20W50 in the summer. 2.6 Mitsus did not stretch timing chains on 20W50 - but you still had to do the countershaft fix, same as you did on 10W30 to get any life out of them. If you could run straight grade 20 on an engine without it being too thick for the conditions you can run 20W50 - and I don't know of a single engine on the market in the last 30 years that can not use straight 20 in the summer because it is too heavy. 20W50 is like 20 that doesn't thin out as much above 100F.
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clare at snyder.on.ca wrote:

And I run 10w30 on everything I own from a 1966 to a 2000 (the manuals on the later ones call for 10w30, the '66 still references single-grade oils but I use 10w30 anyway) and can make the same claim. Two of my engines have exceeded 350,000 miles. Yer point?

I know of *quite* a number of engines that will develop enough oil pressure when cold on 20w50 to put the spin-on filter at risk of bursting.
Besides, thick oil boosts pressure but flows WORSE inside the engine so that its not actually reaching the critical contact points. Viscosity has almost nothing at all to do with actual film strength. There are 0w30 oils with better film strength than single-grade 30-weight.
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<clare at snyder.on.ca> wrote in message

On what basis do you recommend this? Why should we override the Toyota engineers in favor of your choice?
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