Oil Pressures

[DJ194950]

I've been following this forum for 2+ years and have read that 40 psi- 55 psi at higher rpm's is good with an idle rpm when hot is 5psi - 10 psi is also good.

Why is the lower psi ok?, when newer motors including mopar do NOT do this?.

Just trying to understand this. Mine is about 45psi cold and about 10-15psi when fully warmed up, seems no problems, but is just enginerred into the mains, cam bearings, or the oil pump? Expansion of any/all of the above?

Can this be changed? Has someone trying to change this?

I know Ferd and Mopar believed that flow was more important than pressures(pressure = resistance to flow),

but now the ALL seem to into pressures.?

Just curious,

Seems we have some very well trained/experienced forum members,

Thanks for your imputs,

Doug

[Merle Coggins]

This is quite common on all engines, although the pressures may vary between manufacturers due to different configurations.

You are correct that the pressure is a result of the resistance to the flow of the oil. When the oil is cold it is thicker which in itself creates more resistance to flow, thus increasing the pressure. But the pressure relief valve will limit the pressure. As the oil warms up, and gets thinner, that resistance lessens and the pressure will be lower. At higher RPM's there is still enough flow through the system to build pressure in the system, but at idle the flow is reduced, because the pump is spinning slower, so the pressure is lower. Also, at idle the load on the bearing surfaces is less, so that lower pressure is still OK. Here again different engine manufacturers will have different specifications as to what is acceptable oil pressure at idle, but 10 - 25 is quite normal for many engines.

Merle

Edited August 26, 2012 by Merle Coggins

[Plymouthy Adams]

well..big block mopar is only 8psi at idle...the ole rule of thumb of 10psi per 1000 RPM is still pretty much accepted..

[Flatie46]

I hate to have an oil pressure gauge on anything, it's just anthor worry. If you don't have the gauge your not constantly glancing over at it.

Then you just listen for a rattle.

[RobertKB]

I hate to have an oil pressure gauge on anything, it's just anthor worry. If you don't have the gauge your not constantly glancing over at it.

Then you just listen for a rattle.

That's a bit like saying, "I don't want to know my blood pressure, I'll just wait for the heart attack!"

No point in burying your head in the sand.

[Flatie46]

That's a bit like saying, "I don't want to know my blood pressure, I'll just wait for the heart attack!"

No point in burying your head in the sand.

True but I think I'm better off just driving it and not letting it worry me. My old truck has had low oil pressure for years (10 or so) I've been saying when it lays down it lays down. Having the gauge is just like the truck nagging me when I jump in it. Not really burying my head in the sand just procrastination at it's finest.

[54Illinois]

The Plymouth manual I have says any pressure, even low at idle is normal. They only give a pressure for driving...

[Young Ed]

That oil pressure at idle is a minimum. Both of my flatheads have 30-35 at idle even after driving on the hotest summer days.

[W.F. Brown- III]

On my '48 Plymouth I have 40 to 50 psi when driving, but after 20 or 30 miles of driving the pressure at idle will drop to just about off the gage. This has just recently began to happen. Previously, the idle pressure when hot was in the 10 to 15 psi range.

Should this be a concern?

[meadowbrook]

Either your gauge/connections are faulty or your engine has a problem. Any increased engine noise at idle?

My never rebuilt 230 in my 79,000 mile '50 Dodge runs 50 psi hot at 2500 rpm and between 10 and 20 idling hot, depending on how hot.

I use 30 wt oil, BTW.

So it seems that at least my oiling system/bearing clearances are ok.

Compression certainly isn't as I get 100 psi on 5 cylinders and 85 on the 6th. But it runs fine, easy starts (cold) and smooth operation.

It is a bit harder to start hot, which makes me wonder about the compression or maybe I dont have the proper procedure down yet (as in how many pumps of the pedal).

[Niel Hoback]

I think most people, including me will tell you not to pump the gas on hot start. That will make it hard to start.

[DJ194950]

Just time for me to says thanks for all the imputs!

I'd love for the pressure to stay at 30+ when fully warm And driven, but so many say don't worry, so i won't!

Thanks for the feedback.

For Neils last comment on hot/warm starts, I have found that 0 pumping the gas actually made it easier to start. I was pumping it like it was cold and it did not start until i'd finally hold the throttle 1/2+ open, almost wide open.

Thanks to all for the comments,

Doug.

[W.F. Brown- III]

Although the oil pressure in my '48 drops to next to nothing at idle when hot, there is no engine noise. Give it a little gas, and the pressure jumps back to the 40 psi range.

I recently began running 10W-30 oil. Could that be part of the problem? What things could cause a low pressure reading at idle with a hot engine?