What is acceptable oil pressure at operating temp

B

Big_Guys_baby

Senior Member
Hey guys,

I am curious what the acceptable numbers for oil pressure are at operating temp for both idle and cruising speed? I did a bunch of searching but can't seem to find a clean thread discussing "normal" ranges for these engines.

'46 Business Coupe
 
The old adage for a flathead is a minimum of 10 pounds per thousand RPMs. Undoubtedly some may disagree but it works for me.

Tom
 
Something at idle and something higher above idle! Like Vic said, flathead oil pressures seem to be all over the place. A lot of people do go by the 10 psi per 1000 RPM, with that you would end up with 5-10 psi at idle and 25-30 at 2500-3000 rpm. A little higher might be nice, but once you get above 60 psi the high oil pressure can become an issue.
 
I gave my 33 with a later 21 stud a good run last weekend, and it seems to have a sweet spot for oil pressure at about 45 mph. The pressure settles at 35-40 psi with a mechanical gauge. If I run at 50-55 mph for some unknown reason the pressure drops to about 25 psi. As it never went any lower I was happy to cruise in that range.

Mart.
 
Mart:
How many Qt's of oil do you run ? Are you maybe pumping it out of pan faster then it is getting back to pan / making the pump search for oil / just a thought

BILL W
 
Just remember, it's not pressure that lubricates, it's flow. You could have a totally blocked off lubrication system and show as much pressure as the bypass valve would allow on the gauge and not have any oil flowing anywhere. I think that's the concern with too high of pressure as JSeery mentioned. So, technically, any pressure at any speed indicates that the oil is flowing to where it needs to go to lubricate. That being said, most seem more comfortable with more than minimal pressure along the lines of the numbers that have been said.
 
Well, It's not the MPH it's the RPM, depends on gear ratio. My 40 coupe with a T5 and 9in. rear 3:50 gears turns 2000 RPM at 60 MPH. Now tripping with oil all warmed up at 60 mph has 40-45#, if I drop the trans back to 4th, higher RPM about 55#, hot idle witch is 900 RPM with my wild cam and everything else in this engine has 20#, close to 100,000 miles with same main bearings, I did put in a new set of rods bearings at about 50,000 because I broke a second ring land and couldn't get one 3-5/16 piston so had to bye a new set. Walt
 
In My new 280ci engine I run 5-20 oil and have 10 at idle and 40 at 2000. This is at aprox 180 degs. I'm sure the bearings are very happy, because all the oil comilg out of the pump is going through them.
 
Thanks guys! I was mainly making sure my idle pressure was alright. She averages 5-10 around 180 at idle and around 40-60 while cruising.

The oil pressure used to drop off real bad at idle before I did a bunch of work and pulled the oil pan and cleaned out the pickup screen real well. That seems to have helped a lot.
 
The 40 deluxe I just finished, with an 8BA has normal pressure, until it warms up. I have driven it 2000 miles, I have an electric gauge and a mechanical one. After it is warmed up to 180-190 degrees the oil pressure, at idle is 0, 40-45 at road speed. I dropped the oil pan and checked the pump,(bypass valve), pick up, oil level. I hate to destroy all the new bearings, but although no oil pressure, it is quiet as a mouse. I'm running Brad Penn 20-50. If it blows I maybe ready to modernize!!!!
 
I don't feel so bad, I basically get zip at idle when hot.. (Electric gauge) seems a very common thing as soon as the oil is at temp the pressure drops right off, my y block is the same tho I get 10 - 15 at idle with that.
 
I would be concerned about no or very little oil pressure at idle, but a lot of flathead people apparently are not, been this way for very many years!
 
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