This question will be directed towards street driven cars. I have always heard that constant high oil pressure is bad for the bearings. For example, 60 psi at idle and 80 max at high rpm. Is there any truth to this? If it would be an issue, would it happen quickly or take a lot of miles to wear the bearings down?
Oil pressure concerns, fact or myth
- Thread starter duster360
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MOPAR Factory High Performance engines used a 65 psi relief spring while standard engines used a 45 psi relief spring. All those engines would run forever, 100K - 200K, if not beaten to death. The rule of thumb was 10 psi per 1000 rpm. It has to do with the fluid dynamics of the rotating crank journals.
Unless you are spinning 10,000 rpm you don't need that much pressure. 66fs is spot on with the 10psi/1000 rpm formula. Now I would rather see a little higher at idle and not too much at rpm. 30 @idle and 50-60@ 5000 rpm but that's just me. I don't have a manual gauge in my cars because I don't want to worry about the pressure. (if it's too low or two high.) Now, before I get bashed for what I just said, I'll bet I have put a million miles on Mopars since the 70's with nothing more than a idiot light.
I had an engine that hit 100 psi cold and ran it for many happy miles.... Never an oil or bearing problem...
I would rather error on the high side than the low side when it comes to oil. 75-100 psi won't hurt the bearings, but to little will....
Metal to metal will wear the crank and bearings real fast...
I would rather error on the high side than the low side when it comes to oil. 75-100 psi won't hurt the bearings, but to little will....
Metal to metal will wear the crank and bearings real fast...
middleagecrisis
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Costs a little extra horsepower to run the higher oil pressure, but I'd rather have oil pressure that's a little higher than a little low.
67Dart273
Well-Known Member
The big problem so far as I know for higher than needed oil pressure is the danger of rupturing a filter, and damaging / failing something in the oil pump drive.
My old 340, which lived in the old FJ-40 landcruiser, routinely pegged a 100psi gauge
My old 340, which lived in the old FJ-40 landcruiser, routinely pegged a 100psi gauge
Always upgrade to the beefier distributor drive gear with the HV and high pressure oil pumps.
They need the extra strength over the stock shaft.
Not True within the range we are talking about. 100 psi is too high, more likely to blow a filter canister. Too thin an oil is more detrimental to bearings than oil pressure, especially rod bearings.
AJ/FormS
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I'm with you mike.
magnummopar
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Here, at magnummopar, general rule is 20-30 idle and should see 60 by 3K. Been working great for us for 20 years and never a bad bearing.
There was a heated debate about why 10 wasnt ok, I stand by the above with 100's of engines working great to back me up.
As far as "washing" the bearings with to high of oil pressure, I would think whoever told you that has something high, but it wasnt their oil pressure.
Dry sump runs lots of pressure but doesnt rely on cam to drive pump so no hp loss from pump. Regularly run 100+, bearings last just fine.
There was a heated debate about why 10 wasnt ok, I stand by the above with 100's of engines working great to back me up.
As far as "washing" the bearings with to high of oil pressure, I would think whoever told you that has something high, but it wasnt their oil pressure.
Dry sump runs lots of pressure but doesnt rely on cam to drive pump so no hp loss from pump. Regularly run 100+, bearings last just fine.
Ive always liked 20-30 psi at idle, but like stated 10 psi per 1000 rpm works well in most applications. My dart s 360, with a pressure fed lifter solid roller cam runs 35 at idle and exactly 60 above 2k rpm all the time.
To add, when I was working as an operator in a shipping yard some of the older equipment would pretty much make no oil pressure lol. The gauges that worked would read about 25 psi driving around and maybe 2 psi at idle. The gauge would barely read anything. These were big diesels (not sure the type) and because it was shift work they would run 24 hours a day! it was pretty much full throttle everywhere you went pulling 100k pound trailers. The one making the lower pressure had 24 thousand hours on it and it still ran perfect and had good power.
Not that I think thats good, it just shows that things can live with low pressure! LOL
To add, when I was working as an operator in a shipping yard some of the older equipment would pretty much make no oil pressure lol. The gauges that worked would read about 25 psi driving around and maybe 2 psi at idle. The gauge would barely read anything. These were big diesels (not sure the type) and because it was shift work they would run 24 hours a day! it was pretty much full throttle everywhere you went pulling 100k pound trailers. The one making the lower pressure had 24 thousand hours on it and it still ran perfect and had good power.
Not that I think thats good, it just shows that things can live with low pressure! LOL
There's pressure, then there's volume of flow, wash. I read or heard somewhere that GMs 305 being a cam eater was because there wasn't enough wash to lobes and lifters engineered in , even with ample oil system pressure.
Why stop at a 305. All small block Chevrolets are. I never took out a lifter that was not dished from a stock small block Chevrolet.
66fs said:
Indeed it does,
Just by way of 'info'...
http://raceenginetechnologymagazine.com/,
Issue # 30 read the below article, its free...
Focus: FLUID FILM BEARINGS - The magic of crankshaft bearing operation and where it is headed.
Yeah , I know, its not F1 Rpm here in Mopar land, the principals are all the same & have been...
TrailBeast
AKA Mopars4us on Youtube
There is a lot to be said for just driving and having fun with a car and not watching and questioning gauges all the time.
Mopar92
Well-Known Member
Wash them out with what? More oil? Ha!!
moper
Well-Known Member
No truth to washing out bearings. Also - pressure does not indicate flow. Just the opposite. What you are doing is taking engine power and trying to compress a fluid. All that really means is the bypass valve in the pump is open a lot, and you're creating heat in the oil. The best case scenario is the 10psi/1k rpm if your clearances are per the factory manual. If they get wider, the pressure will drop - but that's what supposed to happen. If you run your clearances wider than factory specs, the larger volume pump should be used with the HP oil pump drive.
spoken for truth ... in a pushrod engine Once again,http://raceenginetechnologymagazine.com/,
Issue # 30 read the below article, its free...
Focus: FLUID FILM BEARINGS - The magic of crankshaft bearing operation .
In the 6-9k rpm range at least...
So using the 'tried & true ' formula an 'otherwise prepped' Engine, at say 18k
RPM, would need the same oil pressure ???
18,000 rpm x 10 Psi per = YIKES !!!!
Bearing wash was an issue in the '70s.
Non-sequitur since the evolution of 'Hardened Aluminum Tri-Metal' designs.
Honored Posters, I am not trying to be an A** here, just trying to help.
Thx for the Grace !!!
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