[Super Dave]

Everybody experiences it but I want to know why it happens and if it can be corrected.
At cold temp oil PSI is maxed out at 65psi at 1100rpm. When at 195 deg F and 800 rpm psi is 7-10 psi (yeow-za!) When rpm is increased to 1100 rpm psi is only 40 psi I'm using Mobil 1 but it happens with 10W-40 or straight 30W. I understand viscosity vs. temp but come on! Is it a function of my oil pump bypass spring or what? Bearing clearances? Pump is new as is 454 rebuild.

 

[Harley]

7-10 seems a little low from 65, How many miles on the engine? My work truck with mobile 1 and about 6000 mi. will drop to 20-25 from 65 on a hot day.
Pressure drop is a function of RPM, vicosity of the oil and bearing clearences.
Harley

 

[tom3]

Long running argument about oil pressure. Which is better, high pressure, volume, or stock. Washing bearings, oil film retention, etc. I've seen a bunch of F or ds that ran forever with no indicated oil pressure at highway speeds. I'd guess you got some extra clearance in the bearings. Get some argument here, but I'd suggest a bottle of STP with each oil change and 10W40 oil. I'd also get a 180 degree thermostat. BTW Do you get any rattling or knocking noise when you start the engine after changing the filter until the oil pressure comes up? That would verify the loose bearings. tom

 

[BillK]

Dave,
I would think you have a problem, may be the relief valve in the pump, might be excessive bearing clearances, but if the motor is fresh that should not be the case. Take a look at Melling's site: http://www.melling.com/
they have some very informative articles on oil pressure and the causes of low pressure. The 10W40 oil should be fine, it is the same as 40W when it is hot (Go to Mobil's site for a good explaination of viscosity numbers) and you should not need STP or any other oil additive if your motor and oil system is up to snuff.
40lbs at 1100 rpm is more than enough, GM specs 10lbs per 1000rpm. But 7-10lbs at idle is a bit on the low side. Your motor really should have at least 30lbs at idle with the 10w40 oil in it.
The other thing is to make sure that your gauge is correct. Hook up another gauge just to be sure. If you have any other questions e-mail me, I will try to help.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100

 

[JWagner]

It seems a little odd that the pressure drop from cold to hot would be the same for Mobil 1 as for the petroleum based oils. Mobil 1 should have a much smaller viscosity change than the petroleum based oils. I have used Mobil 1 in engines that were difficult to start in subzero temperatures and no matter how cold it got, they cranked over like it was summer.

 

[Sean]

10lbs is about as safe-low as one would want to go in my opinion for a stock or mild motor.

At this point, raising the idle abit will keep the pressure in a safe range, and then keep a close eye on it once the rpm's are up a tad.

The part that leads me to believe you may NOT have a problem is the 40lbs at 1100 rpm.
Hence, if you set the idle at 950, you might have 20-30lbs??
This is plenty of idle pressure I think most will agree.

my .02

Sean

 

[drptop70ss]

Any cam bearings get nicked when the cam got installed, and are all the cam bearings oil holes lined up?..saw cam bearing problems cause this problem before..

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70 chevelle ss396 conv
66 chevelle ss396 hdp/conv

 

[Super Dave]

Thanks for all the inputs. The 461ci does not clatter when first started. Engine has < 1500 miles on rebuild. The gage is accurate when compared to another. I don't know if I should really worry as cruising nets >40psi at all temps. Additionally, my F-150 460ci experiences the same phenomena although it goes to zero at hot idle (electrical gage). I suppose this is one of those cosmic issues that belongs in Roswell. Maybe an AUTOpsy is in order...