Oil Pressure

When the engine is hot, my oil pressure is about 45-50 under load. At idle, the oil pressure drops down to 20.

I only drive about 3000 miles a year and do an oil change in July before the Crawl, and one in December.


I’m assuming maybe a bad oil pressure sending unit?


Anyone else have an XJ who’s pressure gauge does that?

Check the oil viscosity. Maybe it is too thin for hot days. I try to stay away from the bargain brands. What oil filter are you using? That could restrict the pressure to the gage as well as the rest of the engine.

I use Amsoil 10-40. With ambient temperature in the low 80's, after an hour on the highway the gage show 60 at 2000 RPM and 40 at idle. I uses the Ford FL-1A filter and replace it every 5000 miles. Oil at 15 to 20 thousand miles depending on miles driven in stop and go traffic.

Yeah I have that as well, its always been like that since I bought it 2 years ago. I bought a new oil sending unit but that one broke while installing it so I just never replaced it.

Cottontail said:

When the engine is hot, my oil pressure is about 45-50 under load. At idle, the oil pressure drops down to 20.

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Sounds normal to me. Oil pressure is a function of rpm, not load. Also the gauge isn't overly accurate to begin with. If you have a real gauge you might want to check the actual pressure versus what the dash shows.



From a 97 FSM:
At Idle Speed (600 rpm) . . . . . . . .13 psi
At 1600 rpm & Higher . . . . . . . . . .37 to 75 psi
Oil Pressure Relief . . . . . . . . . . . .75 psi

lawsoncl said:

Sounds normal to me. Oil pressure is a function of rpm, not load. Also the gauge isn't overly accurate to begin with. If you have a real gauge you might want to check the actual pressure versus what the dash shows.



From a 97 FSM:
At Idle Speed (600 rpm) . . . . . . . .13 psi
At 1600 rpm & Higher . . . . . . . . . .37 to 75 psi
Oil Pressure Relief . . . . . . . . . . . .75 psi

Click to expand...

That's great information...and a relief. After blowing an engine in my Commander last week I've suddenly developed a fear of overheating ANYTHING.

Oil pressure varies with engine rpms. 40-50 psi at 55 mph and about 20 psi at warm idle is typical.

I had problems for years with mine as it got hot. I use 20W50, live down where it hits 105 F mid days.

I finally solved two problems that plagued me for years. I am convince I had enough miss fires to slowly dilute my oil with just small amounts of gas and would make mine drop after a 1 hour run on the freeway to 15-20 psi at idle (10 psi years ago...). It is now 25-30 psi at idle min on the hottest days. One was just needing slightly hotter spark plugs on two cylinders, that have just a tiny bit of oil getting by the well worn valve guides that would foul #1 and #2 plugs over time. That led to miss fires, and that led to traces of gas in the oil that thinned the oil which lead to more oil getting past the valve guides to the plugs. Vicious circle! Only took me 14 years to debug that last issue on the 87 Waggy, now at 298,000 miles

It got as low as 10 psi back around 2005. Put in a high flow oil pump then, and used a quart of Lucas for years to deal with it and kept it no lower than 18 psi.... Now it runs a good 30-55 psi with using Lucas!!!

I've herd that if you use a high flow oil pump that it would kill the distributor gear and the gear on the cam that drives the oil pump . because I looked it up and that was people was saying , I would like to run that kind of oil pump .

tech1001 said:

I've herd that if you use a high flow oil pump that it would kill the distributor gear and the gear on the cam that drives the oil pump . because I looked it up and that was people was saying , I would like to run that kind of oil pump .

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I ran mine since about 2004 with the high flow oil pump from AZ. No idea what brand it was. The dizzy was already new, durajunk from AZ.

A few months ago the POS Sheer/role pin died (sheered) that holds the Dizzy gear on the Dizzy shaft. New dizzy installed about 8 months ago now with no problems. Been about 75,000 miles since I did it in 2004.

But then, my oil pressure was down to 10 psi, hot at idle. There is by pass valve, relief valve if pressure gets over 75-80 psi.

I have not read of any one else here using a high flow like I did, that I recall.

I would definitely consider borrowing/renting/buying a pressure gauge to confirm your pressure, but looks like your readings are good/normal-ish.
For idle/low rpm I believe the old school standard was 10psi/1k rpm