High oil pressure at idle????

[wml52]

I recently replaced the 4.0ltr in my 2000 TJ with a Jasper 4.0ltr remaufactured engine. Here's the issue, when I first installed the engine I was getting normal oil pressure between 10psi and 14psi @ idle and around 40-60psi highway driving. Now I noticed that at idle I'm running 60 -65psi and 70-75psi at highway speeds, this was confirmed using a diagnostic pressure gage. My questions are, why would the pressure suddenly change and is this s bad thing???

Would appreciate any help on this one. Thanks!

Bill

[mrblaine]

Originally posted by wml52
I recently replaced the 4.0ltr in my 2000 TJ with a Jasper 4.0ltr remaufactured engine. Here's the issue, when I first installed the engine I was getting normal oil pressure between 10psi and 14psi @ idle and around 40-60psi highway driving. Now I noticed that at idle I'm running 60 -65psi and 70-75psi at highway speeds, this was confirmed using a diagnostic pressure gage. My questions are, why would the pressure suddenly change and is this s bad thing???

Would appreciate any help on this one. Thanks!

Bill

What did Jasper say about it?

[wml52]

I haven't spoken to them yet, will call them tomorrow, but if it's anything like how they handled my transmission I'm not to hopeful anything will be done.
Bill

[mrblaine]

Originally posted by wml52
I haven't spoken to them yet, will call them tomorrow, but if it's anything like how they handled my transmission I'm not to hopeful anything will be done.
Bill

The reason I asked is typically that's an indication of a bad sending unit for the oil pressure gauge, but you said you used another gauge to check it, so it's not a very common issue.

Good luck with Jasper.

[Tumbleweed]

Have you changed brands of oil filters? I have seen a pressure difference in some brands.

[wml52]

I didn't think it would be the oil filter because it had the same filter installed when I first installed the engine, nothing other then the pressure has changed.

[Dukes69]

maybe they put in a high pressure pump? Are you using an electric or mechanical gauge?

[wml52]

Mechanical Snap-On diagnostic gage, my questions stems from the fact that it only recently started to read high pressure, prior to that it was nonimal and within Chrysler specs.

[JLemieux]

Engine oil pumps are "Positive Displacement Pumps". This mean that as long as the pump is turning it is flowing oil. The volume of oil changes with the speed of the pump. Oil pumps do not pump pressure.
Oil pressure is different from oil volume. Oil pressure in an engine is a result of the restriction of the oil flow. An engine with tight clearances will have a higher pressue reading than a worn out engine with looser clearances. Oil flows with less restriction on the worn out engine resulting in less oil pressure.
The high end of oil pressure is regulated by a pressure relief valve in the oil pump. If the restriction is too high for the pump to push the oil, the relief valve opens the excess pressure is bled off. If this didn't happen the pump would self destruct or the shaft that drives it would break.
Now, in your situation you had normal oil pressure and you now have high pressure. The only way for this to happen is to have more restriction in the oil system. This is not a normal occurance. It is possible that your pumps relief valve is set at 75 PSI and at higher engine speeds it is simply bypassing the excess pressure. Otherwise you might see 100 PSI readings.
The filter should not cause this because most good filters have a bypass built in just in case they get plugged up. Even if it didn't have a bypass, I'm pretty sure the pressure sending unit is downstream of the filter so it would show low pressure if the filter was plugged.
As a rule of thumb, 10 psi of oil pressure for every 1000 RPM is acceptable.
I have never seen a Jeep with 65 PSI at idle. My guess is something is plugging up the oil passages.


Hello? Jasper? I've got this problem....

[wml52]

Thank you for a fantastic explanation was very helpful. I had a feeling it wan't normal, sounds like Jasper is trying to dodge the bullet. Will keep you posted!

Bill