Hey all,
I'm new to the jeep world and if I'm being honest to the automotive world in general. About 5 months ago I purchased a 1997 ZJ with 4.0 I6 (hope I got that right). I really love this vehicle so I've done quite a bit of work on it to keep it on the road. I've learned so much in these 5 months and take pride in my ability to do my own mechanical work on my vehicle. I started having what seems to be a common issue with oil pressure in these 4.0s. In the beginning, cold start gauge reads 40 psi and stays at a constant no matter what, idle, all rpms, never moves. Once it would warm up, oil pressure would drop to 0 at idle and shoot back up to 40 while driving. I went to advance auto parts and bought a replacement oil pressure sending unit, however they have changed what they carry and its now called oil pressure switch (all auto parts stores nearby carry this same part). I installed it and now on cold start I get 40 psi reading and gradually drops to 30 psi and stays there at a constant just like before. It never fluctuates, I've been reading a lot and this concerns me because based on everyone's responses on other threads, they seem to average about 10 psi higher then that and that it also should fluctuate from idle to in motion. Any help would be greatly appreciated. Sorry about the long post, I've put a lot of money into this jeep and to have to motor go on me anytime soon would be earth-shattering. Thanks in advance.

P.S. I've read about the new dummy gauges but what concerns me is the one I replaced didn't fluctuate either until it started acting up and even this new one recently has began to every now and again drop to 0 for a few seconds then shoot back up

 

Hi, Griff. Welcome!


First step is to verify your pressure with a mechanical gauge. You can pick up a decent gauge for less than $20 at most auto parts stores. Takes maybe 5 minutes to disconnect the existing sensor and plumb in the mechanical gauge. This is a temporary setup, so no need to carefully route the pickup line. Just drape it across the engine compartment and rest the gauge on the hood or the cowl where you can see if from the driver's seat. Fire up the beast and see what you have.


And by the way:


Yeah, you got that right.