my mother in law has an 03 GC which lost oil pressure, funny thing is when ya turn the key on before ya start its reading 40lbs of pressure,, but i pulled the valve cover off and started it and the rockers are clacking away with no oil pumping up, i do see some sludge , now im wondering do u guys think the oil pump screen is clogged?,or the oil pump just crapped out??? and how much of a PIA is it to get the oil pan down,, 4.0. She bought it used 5 yrs ago with only 65,000 miles now has 102,000,, she always had the oil change at 3000 miles..and where is the oil pressure sender on this motor???

THX

 

Yes, it's on the passenger's side of the block near the rear corner. It kind of hides behind a wire bundle.

Take it out and start the motor. If you've got any flow at all, the pump is fine. My advise is to change it anyway, I doubt the intake screen is plugged, but it could be a internally collapsed filter. Did that make any sense at all? Two thoughts crossing in the fog. Anyway, the pan can be dropped without much trouble, I've been told. I haven't done it myself yet (thank God!). You may have to remove the front driveshaft and starter for working room. The only other thing it could be is a spun bearing--worst case scenario.

 

man i hope its not to bad to pull,, i wanna put my auto meter gauge on it to see if i get anything,, glad she didnt drive far, she was only a few blocks from home when the noise started,, thx for the heads up on the sender,,

 

One other thing. Don't buy anything other than a Mopar sensor. I bought a NAPA Premium sensor and it only reads 20 psi all the time. It actually goes up to 35 when the OAT is -15*F. It has a printed circuit and a crystal in it that is critical for proper function. It was made in Mexico, not China. Mopar's is a bit pricey, but the NAPA one was $49.95.

 

great i sure will,, time to get all bundled up,, there garage doesnt have heat,,, so ready for spring to get here

 

You never said weither it was a 4.0 or a V8. I gave you info on the 4.0 I6. I hope it is. Never mind, I reread your post.

 

There is oil in it, right?

 

How long did you let it run...it can take several minutes for oil to get to the rockers,especially in your cold climate.

 

Several minutes? Maybe 5 seconds, hopefully!

 

Dave,at idle speed it CAN take that long on a cold 4.0 and that is normal,especially if it has been sitting for a awhile. The cold thick oil takes awhile to get through the small orifices of the lifters and pushrods. This is normal and won't harm a thing b/c there is plenty of residual oil in the rockers to provide adequate lubrication.

 

I was more concerned about the bearings. I use 10W30 full synthetic in my WJ and after sitting for 3 days at below 0 temps, it fired right up and I had oil pressure in 3 seconds. It did crank a little slow however. That's a 4.0 at 150K.

SAE says that 90% of bearing wear occurs before oil pressure comes up. I use the 10W because of the mileage although jeep calls for 5W.

 

Oil pressure has little to do with how long it takes for oil to reach the rockers. Yes pressure should build up in just a second or two but that does not mean oil is getting to the rockers. Start your engine after it sat all night and look through the fill cap and you will be surprised to see no oil for awhile.
That is true about wear at startup but it is not the bearings b/c they have enough residual oil to keep them lubed until pressure builds. Most startup wear is on the valve train components b/c it takes this long for oil to get to the top of the head.

 

That may be true, but the lifters are supplied directly off the main oil gallery that supplies the bearings, so they get oil right away. The rockers don't create noise, but lifters do. I would relate valve noise directly to lack of oil pressure. Or bad lifters. Again, I haven't had a 4.0 apart, but if the pushrods are hollow like GM's are, the lifters pump oil to the rockers so oil may be slow coming up.

The oil filter should have a check valve in it to prevent drainback, so the pump should hold a prime. This was a problem with GM V8's that was cured by changing the filter specs.

Again, this is just my opinion, but it has some basis of fact.

 

well it turned out there was sludge in the pan clogging the oil pick up,, also the oil pressure switch was bad saying it had oil pressure before the engine was even running,, so that never triggered the oil light to come,, once i drained what little oil was in there,, only 1 qt,, put a new oil pump and pic up in and clean all the sludge i could see, this thing runs as if it never had an issue,,has 60lbs of pressure cruizing and 40lbs at idle, , thx for the info guys

 

Another testimont to the heartyness of the 4.0! Takes a licking, keeps on ticking!