DMcCall1202

Okay I have read a ton of threads on this subject but still have a ? I have a 2000 Cherokee Sport 4.0 w/ 135,000 miles. When I start it and it's cold oil pressure is fine but after driving and it warms up when I come to a stop and it's idling after about 5-10 seconds the oil pressure drops to 0 and the check gauges light comes on. I put an oil pressure gauge on it and let it run for about 15 mins and oil pressure was 13psi so I put a sending unit on it but did not drive it with the gauge on it. After I put the sending unit on it I drove it home and the light was still coming on so I put the gauge back on with a tee to run the sending unit as well it and after driving the oil pressure drops between 5-7 psi at idle so the light comes on. I am thinking the pump is going bad there is no noise from the engine and it runs fine. Any input on the matter before I replace the pump? Thanks.

DMcCall1202

Oil and filter are new and at correct level(10w-30) and just changed all fluids and did tune up.

freegdr

pump does not creat pressure only flow

Finch

Your sensors prolly gone it's right above the oil filter hook a pressure gage and see if it reads what the dash gauge tells but the 4.0 has bad oil pumps so I'd just do both now before you take out a motor.

freegdr

https://www.cherokeeforum.com/f51/ho...e-works-82130/

Finch

Not necessarily..The 4.0 oil pump pushes oil to the top of the motor if the gauge is reading 0 that means no oil is getting passed the sensor thus the pump isn't pushing oil to the top end quick enough.

Finch

His motor has 139k unless he never changed his oil I would doubt it's that worn lol

crystalion

My oil pressure was notoriously low on my 2000 most of the time -never got so low as to kick off the light though.

I added a oil cleaner product ( many available -many use tranny fluid) and changed to full synthetic 5W-30W--new filter pure 1.

After 2 consecutive oil changed close together each time the pressure came up about 15psi.

Now at idle I get 35-40
at 2500 rpm I get no higher than 55-60

When the oil changes were done with an additive it came out totally BLACK. Even though on the dipstick it looked fairly clean.
I can only assume that I caught an engine before it got bogged down with sludge and my pump screen was probably starting to get clogged..

15K miles later everything is looking good and the oil is getting dirty as it should as the miles go.
the switch to a supposed THINNER oil in my mind is no big deal.

DMcCall1202

I have already replaced the sending unit above the oil filter and have already installed a gauge as posted above.I understand that the pump moves volume but if the pump does not flow enough oil then the engine would not build up as much pressure. Like if you take the same senario as in the video above and you put you finger over the hose to "create oil pressure" but then turn the faucet to only have open which would decrease the amount of pressure coming from the hose would that not simulate a pump not flowing as it should which in turn would create less oil pressure? I have read countless posts above oil pumps causing the issue to what i'm having?

Dan_in_WA

The rule of thumb that I learned is 10lbs. of pressure for every 1000 RPM.

But I'm far from an expert on the 4.0L! 5 to 7 lbs at idle wouldn't normally worry me, but if these engines have known problems with their oil pump, as stated above, it sounds like good advice to me to replace it!

To get you by, you could run a heavier weight of oil, like 10W-40. That would improve the pressure.

Dan

DMcCall1202

I thought about running a heavier oil but I would rather go ahead and fix the problem rather then try and get by. Every where I read they say oil pumps go bad around 125k-150k and i'm in between so I guess thats what i'm doing. It looks to me like the oil pump is starting to go bad not flowing as much as it should and in turn not getting enough pressure or the spring on the pump is not fully closing at idle an d causing the issue but I don't like the light coming on and it's suppose to be at 13 psi idle so i dunno

RAH

The process I was told years ago by an oil rep. for the shop I worked at is change your oil and use a good filter, substitute in a quart of marvel mystery oil. drive 1500mi. and do the same thing again. Then do regular changes after the second time. last oil change I switched to the mgl8a oil filter and noticed a big difference in my oil pressure.

freegdr

theres not really any thing to go bad on a oil pump inside there are two metal gears that turn and push oil,when in there cheacking main bearings and rod bearings needs to be done my napa store has them in stock

DMcCall1202

Yeah I planned on checking all my clearances on everything while I was in there

PolarXJ

Have fun