What is normal oil pressure gauge behavior at idle vs on throttle?
So after my most recent oil change I noticed that pressure while driving was just above 50psi. At idle, pressure will drop to low 40s. I don't recall seeing it behave like this in the past; I recall pressure staying steady at just above 50psi at idle and while driving.
After letting it sit overnight I found that I had overfilled the oil. I drained somewhere between .5-.75 quart and the level was back in the safe zone (2-3mm above’E’).
Test drove again and saw the same behavior after car fully warmed up.
Is this normal behavior or is something jacked up (or about to be jacked up)?
P.s. Yes, I am paranoid about this car. No, I’m not ashamed to admit that.
Oil pressure should be 10psi @ idle. 45-75psi @ 3,000 rpm. If I you're experiencing oil pressure drop, the book says it could be/but not limited to: faulty oil pressure sending unit, clogged oil filter, worn oil pump, oil pump and/or relief valve stuck, etc.
"To test the sending unit, measure the resistance between the sending unit terminal and the metal housing. Should read between zero and ten ohms."
Thanks all. The consensus I am hearing is that this sounds like acceptable oil pressure readings and likely not something bad happening in the engine.
I’m going to check into the sending unit and a manual pressure check for peace of mind.
It is more likely that the overfill of oil jacked with your relief valve and/or spring. Can be removed and inspected. Unfortunately, the service manual does not go into any detail for that specific task.
Typically a drain and refill can do the trick on most other vehicles with a stuck relief valve.
Question on the physics of the relief valve. If it were stuck open, wouldn’t it be showing low pressure at idle at all times (i.e. at startup and after warm up)? My idle pressure is only dropping to ~41/42 psi after about 15-20 minutes of running. It is rock steady at 51/52 psi at idle at startup through 15 ish minutes).
Edit: I suppose if the valve is partially open, low temp viscosity could mask any bleed off through a partially open valve. Then as oil reaches temp and viscosity decreases, the effects of a partially open valve are now detectable?
Last edited by Mrama004; April 9th, 2020 at 08:55 AM.
seems right where its should be to me. Anything over 7 psi used to be the bottom point. A late friend of mine used to drag race and he built his own engines. He would never run more than 5 psi because he said it stole HP from the engine if the clearances were tight enough to raise the pressure.
AJ, agree, pressure readings are in spec. I’m more concerned with the abrupt change in oil pressure readings than the actual number. My dumb neurotic brain wants to know ‘why now?’ and ‘how do I bring it back to what it was a few days ago?’
Last edited by Mrama004; April 14th, 2020 at 07:07 PM.
Did you change your filter to another brand? Just spin off the "new" filter you just put on and try either a same one or another brand just for giggles. Easy to do and rule out the filter messing with your pressure.
I use mobil 1 10w-30 and the mopar viper spec filters consistently.
However to Ellow’s point, I came to the same idea a few days ago. I had not yet discarded the previous oil and filter. So I put in the old 10w-30 and put the old filter back on to see if there was any contribution from either of those elements. Pressure readings were exactly the same, ruling out the new oil or new filter as contributors to the change.
Is it possible that it was always like this and I just never noticed? Anything is, but I’m still not convinced that this has been going on and I am just now seeing it after 19 years and at least as many oil changes. However since the pressure readings are perfectly in spec, I also don't want to throw tons of $$ at what amounts to an academic issue at the moment.
So here is where I am on this:
1) check pressure relief valves
2) if they are fine then I’ll just keep my eye on the oil pressure and recalibrate this as my current normal.
The other probable issues in the SM seem like they would require getting into the engine. That seems like excessive work for what are ultimately in spec readings. However do tell if I am missing a warning signal that suggests the work is worth it.
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