oil pressure issue

ok at cold start at idle it is at 40 psi as you run it for like 8 mins the oil pressure goes downvery slowly not fast very gradually it happens when it warms up.. it goes the whole way to zero and the check gauge light come on. when you press the gas the gauge goes up alittle. there is a light i mean a very light light ticking noise. im hoping it is a oil pump it is a 1999 jeep cherokee with 120000 mile on it . i really need you guys help i did change a oil sending unit on it changed the oil multiple time like three times im using a mopher oil fillerplus used different weights to i need you guyes help dont know what to do

I would hook up a mechanical oil pressure gauge to confirm it's actually going to 0. No sense in ripping it all apart if it is just a band sending unit(even if it's new).

I agree that VERIFYING your exact oil pressure with a mechanical gauge is the best idea.

You can often rent them from many parts store....call around.

Good data = good decisions. And until you verify your oil pressure, you aren't completely sure.

what if the mechanicial gauge reads the same thing what do you think it is

Yes, you should def check the oil pressure to verify. But I would say its prob the oil sending unit. Go to the dealership, do not buy aftermarket. I have fixed MANY of chrysler products by replacing the sending unit with OE parts. A lot of the time, they had just replaced it with a junko aftermarket part, but the OE fixed it.

If you are losing pressure, the two most common probs with the 4.0 is oil sludge (pickup screen and oil return holes) and the front cam bearing wearing out. If you are losing pressure, drop the pan and pull the V/C to check the pickup and oil return holes for sludge.

If you don't see massive amounts of sludge piled up, I would replace the front cam bearing. The aftermarket sells a kit for just that. If you buy a factory bearing, you will have to have it machined to fit. If you have a worn bearing, there will be metal shavings in the oil and throughout the engine. The best repair would be a rebuild, but I have replaced the front bearing and flushed the oil and the customers jeeps are still on the road today..

I have seen 3 Chryslers this week with the same prob, and factory sending units fixed them all. I'm not sure if its the temp rising from summer, or what.

Just my buck o five...

When I first purchased my '89 XJ it had the same problem as yours. The first thing I did was replace the oil sending unit. However O'Reilly had two different sending units listed for an '89 W/ the 4.0L. Ensure you replace the sending unit with the proper replacement. I agree with the other posters here. Use a mechanical pressure gauge to verify actual oil pressure. As far as your "ticking" noise, higher mileage I6 engines tend to have a normal light ticking sound. A spark knock could also be mistaken for light lifter noise. How are your plugs and wires?

i did use napa oil pressure sending to replace it or are they junk or should i go get an oem replacement and were would you be able to rent a mechanical oil pressure guage

ok i bought a a mechanical oil pressure gauges i put it on and it is doing the same thing as the electronic one now what

If you have confirmed very low oil pressure, you have a "clearance" problem somewhere in the engine that is preventing the pressure from being what is designed to be at.

The cause can be the oil pump or the engine bearings.

What is your engine coolant opeational temperature? High coolant temps will lower the viscosity of the oil. 120,000 miles seems awful early for main bearing failure but it happens. Failure that early usually means poor preventative maintenance. My '89 XJ has 194,600 miles and carries 25 psi warm at idle and over 40 psi under load warm. A temporary fix would be to use a higher viscosity oil. Also try using Lucas oil stabilizer. I use it at every oil change. Just replace one quart of oil for the Lucas and see what happens. However it looks like you will be pulling the oil pan either way.

the temp is all good not using coolant if it needed a oil pump would the temp go up give me a percentage that it is the bearings for a jeeep that i has 120000 miles on it the bearing should no way be out of it them 4.0s are some stong ass motors i dont know i just hope it is not the the damn bearings

10 mins ago i just put oil sludge additive still no help

Oil pumps control volume and have minor success raising pressure. If your pressure is dropping at operating temps it is a clearance (low restriction issue) and most likely cam bearings. These 4.0s are stout and can run a long time with low oil pressure problems but it is just a matter of time before you need to go through the engine. I've lost bearings as early as 130K and have engines with over 180K and no problems....just jinxed myself.

zinc additives are a good idea, even with synthetic motor oil. today's motor oils are down to like 50 parts per million

Pull the pan, change the oil pump, what the hell if it doesn't work you'll have a new oil pump for the rebuild. The screen may be plugged, who knows. May as well do the rear main seal while your at it.

ok another thing im goingto go pass you guys if it had a bad cam bearing when you press gas the pressure gauge would not go up at. well mine does

It goes up because the pressure is also going up due to higher RPMs of the oil pump. When you said you used different oils what viscosity did you try.
Ron

I am having the same problem only mine at cold idle will be at 40 psi and I can let it sit and idle untill it is completly warm and it will stay anyware from 30-40 psi. when I drive it it stays at 30-40 psi but as soon as I let it idle down to warm idle it goes to 0 psi. when I gas it it returns to normal pressure. But these reading havnt been consistant, One day the oil pressure is showing good at warm idle, the next day it isnt. The motor only has 116,000 miles on it. I'm thinking its a sending unit, what do you think?