4.0 Oil Pressure

[FUNKYTEE5]

I have started seeing slightly erratic oil pressure readings on my 4.0. I have read some accounts where people have stated that the oil pumps are prone to wearing out around 150k or so. I just turned 144k. 20k ago it had 80psi cold and never went under 50psi warm. Now it's 50 cold, and never goes above 50psi warm (10w-40) and idle has dropped to 25psi warm. I'm suspecting that it may be a worn out bypass spring? If the mains were loose then it'd drop pressure under load right? Any oil pump's to avoid? Thanks for input.

FUNKYTEE5

 

[5-90]

Have you rechecked your oil pressure with a mechanical test gage? NEVER assume that the electric is always right - keep a mechanical around for regular checkups. If the sender starts to go, it can look like a pressure problem.

I'm cranky - I do quarterly maintenance checks...

5-0

 

[FUNKYTEE5]

Haven't yet! I actually have one laying around. I replaced the sender last year hoping that it was going bad but it did the exact same thing after installing a new sender also. If i can find a place to tap some pressure, the mech. gauge will be my next try! Thanks.

FUNKYTEE5

 

[5-90]

Just remove the electric sender and screw in the gage nipple in its place.

If you do this often enough, it may be worthwhile to go to your local Fluid Power parts dealer and get a set of "shutoff" quick disconnect fittings - I put the males on my engines and the female on the gage. I can now plug in my gage with the engine running, check pressure, and pull the gage losing only about a drop of oil with the engine going...

5-90

 

[Wil Badger]

mine started to do the same thing so i put in a mechanical oil and taped the gooseneck for temp as well

just fit in this spot to .i had to poke a small hole in the dash/heater vent that goes behind them to make the temp sender fit

 

[5-90]

How did you plumb the temperature sensor? It requires constant flow across the tip for an accurate reading, which is why you can't drop them in just anywhere (like a pressure sensor.)

I'd be interested in seeing how you did it, especially if you got a good flow across the sensor tip...

5-90

 

[FUNKYTEE5]

Just remove the electric sender and screw in the gage nipple in its place.

If you do this often enough, it may be worthwhile to go to your local Fluid Power parts dealer and get a set of "shutoff" quick disconnect fittings - I put the males on my engines and the female on the gage. I can now plug in my gage with the engine running, check pressure, and pull the gage losing only about a drop of oil with the engine going...

5-90

Ok, I just put a tee in so I could use both at the same time. The mech. gauge reads a lil higher than the dash gauge, but still acts in the same manner? Is the oil pump starting to die? Thanks. BTW, good idea about the quick connects!

 

[Mike@Accurate]

Good oil pressure cold, getting worse hot, is the classic sign of bad main bearing clearances. It could be that you are just getting worn out. It is most likely not pump related. The pumps don't really wear out at any specific mileage. Sounds like mains/crank to me. 150k mi is getting on in the years. 80psi was high. 25 at idle warm is acceptable (considering). My 2000 hovers around 40-50#. MIKE

 

[FUNKYTEE5]

Good oil pressure cold, getting worse hot, is the classic sign of bad main bearing clearances. It could be that you are just getting worn out. It is most likely not pump related. The pumps don't really wear out at any specific mileage. Sounds like mains/crank to me. 150k mi is getting on in the years. 80psi was high. 25 at idle warm is acceptable (considering). My 2000 hovers around 40-50#. MIKE

At say a steady 2500rpm is it normal for the pressure to fluctuate up and down 5-8psi or so? I've always had a jumpy dash gauge and figured it was the sending unit. Now the mech. gauge also reflects the same behavior.

 

[Dr. Dyno]

According to the Jeep owner's manual, the oil pressure with the engine hot should be 13psi minimum at idle, and 37psi minimum above 1600rpm.
It's normal for the oil pressure to be higher when the engine's cold and then decrease as it warms up simply because as the oil gets hotter, its viscosity decreases. An oil pressure of 50psi at idle with the engine cold is not unusual, but I'd be uncomfortable if it dropped to less than 20psi when hot. Below 13psi, the lifters won't pump up and you'll hear lifter noise.
The oil pressure will also depend on the grade of oil used; higher with 20W-50, lower with 0W-30. If your oil pressures are on the low side of normal, a thicker grade of oil could raise them 5psi or so.
A fluctuating oil pressure gauge is usually caused by a faulty sending unit but if a mechanical gauge also shows the same thing, it could be an early sign of impending oil pump failure.

 

[Wil Badger]

i made a "t" with the mech closes to the neck and the stock at the top .you can also use the old hole in the drivers side of the radiator .the closed style systems used this. anything with the cap on the radiator will have this spot open to place the mech in or relocate the stock to .i just got lazy and did it this way till i could move the stock to the old place on the radiator

 

[FUNKYTEE5]

I finally got the oil pressure issue worked out. I didn't suspect the mains just because the motor is in really solid shape and not abused. So, I pulled the oil pump and to my suprise it was aluminum? I tore it apart and found that the drive gear was digging it's way into the body of the pump. The input shaft was worn bad enough to let the drive gear hit the case. It's kinda wierd though because the driveshaft for the pump is obviously some type of hardened steel and it rides in the aluminum! Anyways, I got a new Sealed Power pump and it was nice and burly cast iron Installed it and voila! I've got 70-80psi cold, 60psi warm, and never under 40psi at idle. Thanks for the input everyone!

 

[Mike@Accurate]

Aluminum ? Wow, that is the first one of those I've heard of. Especially factory. I'd venture a guess it was replaced somewhere along the way. Is there a name brand on it ? Just curious, MIKE

 

[FUNKYTEE5]

Aluminum ? Wow, that is the first one of those I've heard of. Especially factory. I'd venture a guess it was replaced somewhere along the way. Is there a name brand on it ? Just curious, MIKE

Factory Mopar! Idunno if the pump had been replaced by a later pump or what? It's a 93 4.0 and I got it with 103k miles on it. I've put almost 45k on it and at about 133k is when saw the oil pressure start to go funky on me. I can't figure out why they'd make a aluminum pump case? It costs more and most likely wouldn't be as durable as cast iron case! Go figure?

 

[rsalemi]

Aluminum - yes They are probably all aluminum - the 99 I rebuilt had an aluminum pump which gives 50# in the Drag engine.

 

[Mike@Accurate]

I've probably taken apart 50 4.0's, from RENIX & 258's to '01's, and NEVER have seen an aluminum pump. I have bought hundreds of 4.0 pumps and never gotten an alumimum one. Learn something every day. MIKE

 

[Bloose]

I've probably taken apart 50 4.0's, from RENIX & 258's to '01's, and NEVER have seen an aluminum pump. I have bought hundreds of 4.0 pumps and never gotten an alumimum one. Learn something every day. MIKE

The one on my wifes '01 from her Wrangler was aluminum too. The replacement motor was an '03 from a grand and it was also aluminum. The replacement HV pump was iron though.

B-loose

 

[Mike@Accurate]

What year is Funky's 4.0? I just assumed that it was "older" when he said it had a bunch-o-miles on it. Are the aluminum pumps on "new" (last few years) trucks? I have to admit, the yards around my parts are not really flushed with these yet. Maybe I need to tear apart some newer motors for kicks. What were they thinking anyhow? Aluminum and oil pumps shouldn't really be used in the same sentence. MIKE

 

[FUNKYTEE5]

What year is Funky's 4.0? I just assumed that it was "older" when he said it had a bunch-o-miles on it. MIKE

Mike, it's a 93 Sport with 144k. It is all original as far as internals go besides the new oil pump. I've never heard of or seen any oil pump that wasn't cast iron! If you were to get any gunk build up in the pan, then it may just send enough grit through the pump to eat up the case and send the clearances overboard.

Funkytee

 

[Bloose]

Though there is no question I would prefer a cast iron pump, aluminum pumps are fairly common for OEM applications. I'm sure it's because of lower machining time, and longer tool life when machining. The way a oil pump is built the majority of wear should be between the steel cover plate and the steel gears. There should be plenty of clearance between the aluminum housing and the pump gears. Unless you pick up a fairly large chunk of crap (which should be screened out by the pick up screen) aluminum should be fine and shouldn't wear any faster than an Iron pump.

B-loose