Oil pressure spikes / drops in my jeep

Ok, basic information first I suppose…

1996 jeep grand Cherokee, I6, 111,000 miles.

Bought used with 99,000 miles almost a year ago. No major damage or repairs I now of. very small main seal leak. Driven daily in heavy city traffic.

About a week ago we had our first real cold snap here in New York City. On two mornings in a row I started the truck and imeideatly drove to work without letting it warm up. On the third morning I noticed the oil pressure spike to about 40 (normally it goes to 20 and stays there, hot or cold) and then dip down back to 20, then spiked again to 40. This went on for about 10 minutes. I checked the oil and was about a quart low. I put in a quart, drove and the problem is still there. I was due for an oil change anyway so I got the oil and filter changed. problem still there. The pressure drops back down to 20 and stays there when I’m on the gas, then at a red light after a few seconds the spikes start again till I get back on the gas.

I believe oil pressure sending unit may be the issue because there is no leaking oil, no smoke and no real loss of power. Could it be anything else? Should I be looking for anything else?, and how would cold starts cause this issue?

Thanks in advance for your replies!

I would make sure you have the right oil “weight” in that engine. I will assume that is the case since you say you recently changed the oil and hopefully the shop knows what they are doing and are also in the same area temperature wise.

First guess would be the oil pressure gauge sending unit. You can temporarily (or permanently) mount a mechanical gauge to know for sure what the pressure is doing.

I am suprised that you consider a reading of 40 psi a “spike” and a reading of 20 psi at speed,when warm “normal”. Perhaps they are normal for your exact engine but it would fit in with the rest of the crowd better if normal pressure at speed would be 40psi and a “spike” would be something in the 65 psi range. I am making a mistake in that I am not familar with the peculatities of this engine type and I am applying values that were normal for other engines. I do wonder what is going on with yours that puts it so far off the mark set by other engines. I ask myself if these readings are influenced by how the engine is designed and my inital thought is "no’ but there is something going on here.

everything looks all right

To be hones im not sure what normal is. what causes (and what fixes) low pressure?

Bearing wear is the number one cause of low oil pressure, followed by pump wear(either in the relief spring or actual gears) and even the wrong viscosity of oil to a much lesser degree