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View Full Version : Oil Pressure - should this worry me????



Murphy
07-31-2002, 10:52 PM
On my rebuilt, modified sbc I'm registering 80 psi oil pressure cold. Hot it holds steady at 65 psi and never drops below 40 psi even at idle. Oil is straight Valvoline Racing 40W. The oil pump we installed is a stock unit. The hot pressures don't alarm me too much, but 80psi just seems on the high side. What think you???

Thanks,

Murph

MOP
07-31-2002, 11:05 PM
Sounds like good pressure to me, thats what my 302 runs at :D

CDMA
07-31-2002, 11:48 PM
My new stock 350 ( I use stock loosely) has the same sysmptoms. My engine builder said it is what he wanted...

Chris

Scott Pearson
08-01-2002, 05:34 AM
My BBC pushes about 100 psi when its cold. Thats 20w-50.

(NJ)Scott

Moody Blu'
08-01-2002, 10:36 AM
im pushing 80 psi cold in my 351w and thats with 10w-30 mobil 1

Rootsy
08-01-2002, 10:45 AM
that's a beautiful thing :) and your motor thanks you for it!

blackhawk
08-01-2002, 11:20 AM
My 502 is about 80 when cold and about 40 when hot at idle. That's straight 40w also.

Woodsy
08-01-2002, 11:33 AM
You guys need to check your oil pressure with a calibrated mechanical gauge. Most electrical oil pressure gauges are off 10-20PSI on the high side. Tey are also not linear, meaning that it could be off 20PSI at high rpm and only be off 5PSI at idle. Most stock oil pumps range anywhere between 40-65PSI at operating RPM. If you truly have 80 or 100PSI for oil pressure in your engine, rest assured it would be leaking out of every seal possible unless you used the high pressure seals during your rebuild. Not to mention, you would probably be scavenging your oil pan dry, the oil pump would be pumping oil faster than it could return to the bottom of the engine.

Woodsy :D :D

Steven Cohn
08-01-2002, 11:42 AM
Murphy,
I may have a lot of nay sayers, but I don't agree that 80psi is good. Most GM-based V-8s call for 40 psi @ 2000 RPMs. I don't know what rings, pistons, bearings, temps., oil pump,... you're running. However, a lot of specs. don't call for 40W oil or 80 psi ~ at what RPM did you say? I'm a licensed master mechanic and know a little if not anything about the subject. Your oil pressure depends upon alot of variables. Consider this ~ you spend more for racing oil and run your motor with a high viscosity oil. If the motor has tighter than stock tolerances you're not getting enough oil to lubricate the bearings and rings. One could have high oil pressure, but low lubrication. Think about it. Most marine motors call for a 30W oil.
Steven

Murphy
08-01-2002, 12:09 PM
Thanks for the replies. I'm fairly certain about the 80psi because I have a MasterLube pre-oiler installed and the liquid filled guage reads an honest 80psi when it recharges. I think I will move down to a 30W Valvoline Racing oil & see what that does. The comment about getting good oil pressure but poor lubrication stikes me as a real possibility, especially during cold start when the 40W is at it's thickest. From what I've read in performance books and articles there is a concern that many boats are operating on oil that is too thick and too cold. The rule seems to be that at proper operating temp when the oil thins, the lower viscocity provides better lubrication and places less load on the oil pump and consequently on the engine. I know we've kicked the oil topic to death but I'm still interested in hearing what others think.

Murph

Moody Blu'
08-01-2002, 12:15 PM
Wheres big griz when ya need him. wink

I think hes the OIL torture testing king wink :D

btw im running a melling oil pump and have brand new claibrated gauges from gaffrig.
I understand what your saying about electrical oil gauges but if its new and from gaffrig I woudl think it is top notch, wouldnt you?
I'm not arguing just questioning..

Rootsy
08-01-2002, 12:20 PM
by chance, high volume oil pump?

basic fluid dynamic laws dictate that in order to pump more volume of a fixed viscosity and density fluid through the same passage in the same amount of time more energy (larger Delta P) is required. the pressure drop (Delta P) across the system is the energy required dictating a higher discharge pressure from the pump... if the pump geometry is able to obtain the necessary discharge pressure to move the volume without cavitation then the result is higher discharge or gauge pressure... this whole system is balanced by the pressure relief valve in the pump but in order to move the volume properly the spring is stiffer than in a stock replacement pump, resulting in higher discharge pressure... :D

MOP
08-01-2002, 12:31 PM
Been doing this stuff awhile I really belive in decent pressure, the load on a marine crank is many times higher that automotive use. 68-80 is quite common, I have electric dash and mechanical engine compartment gauges. They read the same, my feeling if you are hammering an engine in a boat with less than 30-35 its not long for this world.

Woodsy
08-01-2002, 12:57 PM
Just got off the phone with Mercury Racing. The oil pressure specification for Mercury Racing & Mercruiser V8 engines is 30 - 70PSI @ 2000RPM. This is with a 25W-40 or a straight 40 weight oil. You can also run 20W-50 as well. This is what they recommend on all of thier supercharged motors.

Here is a neat explanation of oil, viscosity and grading...

http://www.valvoline.com/carcare/articleviewer.asp?pg=ccr20010101ov

Woodsy Von Donzi :D :D

Steven Cohn
08-01-2002, 01:36 PM
Woodsy,
Good link.
Steven

mattyboy
08-01-2002, 07:56 PM
I'm not the mechanic but, I'll take the same approach has I do with my Dr.
high blood pressure is better then no blood pressure at all!!!!!!

Matt

Donzigo
08-01-2002, 08:11 PM
Best post and replies I've read in a long while. I have learned a lot, good info & good link Woodsey. Thanks to all, don't stop now, there's got to be more.

HyperDonzi
08-01-2002, 09:19 PM
Jamie Root,
for a second there i thought maybe someone had proven you wrong. but now i am starting to wonder, will that ever happen?

MOP
08-01-2002, 09:42 PM
Great link thanks a bunch! Nice to get some straight talk.

KMLFAMILY
08-02-2002, 09:06 AM
My .02. All good engine rebuilders replace the stock oil pump with a higher volume pump A- For longevity, as motor becomes worn tolerances increase and pressure will still be there. B- If engine becomes overheated or oil breakdown occurs (cheap insurance).The higher volume pump also increases oil pressure as this increased volume can not be forced into the oil circuit,passages,lifter bores,etc.This is where your higher than stock readings come from.A high volume pump will not increase crankcase pressure-oil leaks etc.The pressure is in the oil circuit and restricted there.You also will not pump pan dry unless oil returns or filter plugged due to the fact 5-7 qts will not fit in the oil circuit. On a high rpm motor windmilling can occur scavenging the oil pan thus the windage tray, knife edge cranks etc. Just a couple of my thoughts.

Scott Pearson
08-02-2002, 05:40 PM
Woodsy,
That is pressure. I have liquid filled Autometer gauges and they are machinacal not electric. I get almost 100psi. No leaks after 14 years. And I shift the car over 7,000 rpms. I wait till she heats up......Laughing!

(NJ)Scott