Constant 20 psi oil pressure in 01 GC 4.0l

[Cmobile]

My son has an 01 Grand Cherokee with the 4.0l, 130k miles. We've had a bit of engine trouble lately and I just paid $600 in engine work, cps, injecors, plugs...

I usually don't drive it, but today I noticed the engine oil pressure gauge takes about 6-8 seconds to reach 20 PSI. Running Rotella 10w-30. This is with a warm engine.

It always reads 20 psi, at idle, at highway speeds, OD off, neutral at 4000 rpm, doesn't matter, always 20 psi.

The oil sending unit was replaced 6 months ago. I bought it from O'Reilly's.

I'm used to seeing oil pressure increase with engine rpm on my other vehicles. Is this normal to maintain 20 psi regardless of engine speed?

I read a lot about the oil pump replacements, dunno. I'll check pressure with a mechanical gauge before the oil pump, but was hoping someone could enlighten me a bit before I dump any more money into this Jeep.

Thanks

 

[heynow]

There is a good chance that the gauge is not designed to show actual pressure. More of a "dummy gauge"

 

[901Memphis]

Originally Posted By: heynow
There is a good chance that the gauge is not designed to show actual pressure. More of a "dummy gauge"


Yep I'd agree if we're talking about the one in the factory cluster

 

[SwampSurvivor]

At some point around then, they stopped having 'real' gauges. My 2000 Cherokee would be one of the last Jeeps to get a real gauge.

 

[AandPDan]

Put a mechanical gauge on it to verify - but it is likely a dummy gauge.

 

[dlundblad]

Interesting.

Mine just goes to about 12:30 once the engine is on.

 

[horse123]

Originally Posted By: AandPDan
Put a mechanical gauge on it to verify - but it is likely a dummy gauge.


Are these gauges that just go to the middle and stay there without actually being connected to anything?

 

[Cmobile]

I'll put a real gauge on and verify.
Just seen a lot of other posts regarding jeep oil pressure and others have movement.

 

[UltrafanUK]

Originally Posted By: Cmobile
My son has an 01 Grand Cherokee with the 4.0l, 130k miles. We've had a bit of engine trouble lately and I just paid $600 in engine work, cps, injecors, plugs...

I usually don't drive it, but today I noticed the engine oil pressure gauge takes about 6-8 seconds to reach 20 PSI. Running Rotella 10w-30. This is with a warm engine.

It always reads 20 psi, at idle, at highway speeds, OD off, neutral at 4000 rpm, doesn't matter, always 20 psi.

The oil sending unit was replaced 6 months ago. I bought it from O'Reilly's.

I'm used to seeing oil pressure increase with engine rpm on my other vehicles. Is this normal to maintain 20 psi regardless of engine speed?

I read a lot about the oil pump replacements, dunno. I'll check pressure with a mechanical gauge before the oil pump, but was hoping someone could enlighten me a bit before I dump any more money into this Jeep.

Thanks


First of all, oil pressure senders are very reliable IF you fit a certified OEM standard one, preferably one from a dealer. Secondly, you should use an OEM oil filter if you can afford the few extra dollars.

At 130K miles it's worth thinking about moving up one grade to an 0 or 5w40 and that should help the oil pressure slightly.

Have you ever seen the low oil pressure light flicker at warm idle just after a good run ??

PS: Get the actual hot & cold oil pressures check if this engine has a childs OP dial wired to the ignition.

 

[SwampSurvivor]

4.0Ls are known for having weak oil pumps. A heavier oil on a worn out old oil pump is going to starve the top end of oil.

 

[DoubleWasp]

Test with a mechanical gauge before doing anything else. I mean, literally don't even waste another second of thought until you verify oil pressure with a mechanical gauge.

 

[Cmobile]

I have been using wix filters, I feel confident they are every bit as good as Mopar OEM.

Quote:
A heavier oil on a worn out old oil pump is going to starve the top end of oil.


Should I stick with recommended 10w-30 or go with a wider viscosity spread, 5w-40 as recommended by ultrafanUK?

Testing oil pressure today. I'll post results.

Thanks for all the advice and suuggestions.

 

[jeepman3071]

+1 on the dummy gauge. Apparently after 2000 the Grand Cherokees had a dummy oil pressure gauge. Probably because the normal oil pressure gauge would swing back and forth as it is supposed to and caused concern.

I'd stick with the 10w30. My best UOA on my Jeep was with PYB 10w30. There is a thread on the Jeep Strokers forum and it has a compilation of wear numbers from stock and stroked 4.0 engines. There wasn't any notable difference between a 30 and 40 weight oil.