Low Oil Pressure Solutions?

dustmagnet30 · 11-28-2010, 01:01 PM

I know I've seen this issue all over the threads, but I never find any solutions. I'll explain my situation and hopefully somebody can help me out.

I have a 2002 Grand Cherokee Laredo Sport - 4.0L straight 6 and 128000 miles on it. I am reading low oil pressure when my engine warms up to operating temp. Pressure is fine on cold start and stays up until the engine temp gets up to about 210. At that point is slowly starts creeping down and will fall all the way to 0 at idle and will go up as the RPM's go up. Eventually it will hardly hold above the bottom line driving and will activate the light when I idle.

I have replaced the sending unit, still got the same results. Checked the oil pressure with a mechanical gauge, same results, pressure goes down as the engine heats up. Oil level is maintained. Not sure if it is the cracked 0331 head because it's a 2002.

Is there any thing I can do to resolve this issue without replacing the engine? Motor sound great, no noises. I've heard about putting on a high performance oil filter, using seafoam additive, replacing valve cover gasket, replacing the black rubber elbow and tubes that go into the rear of the valve cover.

Any thoughts would be great. Hate to have to pay the mechanic 3500 to put in a reman. engine....the car is in mint condition.

Thanks for the help, sorry about the long post, just wanted to be thorough.

nlynd1978 · 11-28-2010, 02:13 PM

ok, start with check your oil level, are you due for oil change? Oil filter can be clogged, then you may need to drop the pan, check your pick up screen, look for sludge. At that point your now going to be needing to check your bearing, seals, piston rings. Oil lubrication systems are a controled leak. Pressure is made by more flow less leak. You motor with 128000 miles has plenty of warn parts that due to many cold start ups where the vehicle was driven, or other issues have warn over time allowing more oil to "leak" then manufacture spec. Oil pumps do not make pressure. they make flow. Tho the oil pump could be the culprit (not flowing as much oil as nessecary) this is less likely the case. Are you consuming oil between oil changes? How much? Do you burn oil? need to pin down what is causing the low oil pressure. Sending units usualy dont go bad, and if you put a mechanical gauge on your engine and had the same problem there was no need to replace the oil presure sending unit.

SplitNail · 11-28-2010, 02:16 PM

Run a thicker oil if everything checks out. Amsoil has some great oil choices that I can get for you if you are interested. I would definitely have the pump looked at/ replaced and if then if everything is okay run a good motor flush to remove sludge and other things and run a thicker oil.

nlynd1978 · 11-28-2010, 02:17 PM

Could be the pressure relief valve on the oil pump is stuck or sludged open. This also would cause low oil pressure.

Also make sure your putting the right oil in the motor. to light of an oil, will thin out more then needed as well as older oil that has lost its thermal viscosity.

And check your engine temp. Is your engine running hot, i dont mean over heating but are you runnng hotter then normal, ie 240-260 degrees or more.

nlynd1978 · 11-28-2010, 02:19 PM

do not run a thicker oil. That wives tail is bad for your vehicle. Your only fixing the symptom not the cause. You will just have more problems down the road when something fails. Plus to heavy of an oil can build your pressure up to high that you will rob torque and horsepower from the vehicle increasing gas millage.

Also it can erode your bearing faster when your oil pressure is to high, which will lead to a repair/replacement of the motor.

Valve cover gaskets are less likey the culprit unless you have a leak coming from them. Tho there is not that much pressure in that area. Oil flow internally thru the block in galleries. the vavles get oil pushed to them then it "leaks" back down into the block thru groves and holes. No significant pressure is build there. Check the oil lines for leaks as well. to your oil cooler, and from the block to the head if its an external line.

SplitNail · 11-28-2010, 02:23 PM

By running a thicker oil I really meant make sure you choose the right oil for altitude and temperature outside. I didnt mean just go toss in some 15w-40 and run with it. Sorry for the confusion. He might be running like a 5w-20. In Dallas a good 10w-30 should be fine.

dustmagnet30 · 11-28-2010, 02:31 PM

Oil level is fine...I do lose between changes due to leak or burnoff i guess, but maintain the level. Not due for another 1000 miles or so. I always run 10w 30 like it says in the manual, I figured a heavier oil would be harder on the engine, especially on cold start up. Engine runs at a consistent 210 degrees after warm up.

I replace the sending unit before I checked it manually as I heard that was the culprit 9 times out of 10.

Took it to the shop for the guy to do the same thing, put a mechanical gauge on, charged me $75 and told me I need a new motor....not very thorough.

Could it be the oil pump if the pressure is at normal level on start. That guy didn't seem to think so. I even asked him about the possibility of a cracked head and he said that wouldn't cause low oil pressure...

nlynd1978 · 11-28-2010, 02:32 PM

Quote:

Originally Posted by splitnail

By running a thicker oil I really meant make sure you choose the right oil for altitude and temperature outside. I didnt mean just go toss in some 15w-40 and run with it. Sorry for the confusion. He might be running like a 5w-20. In Dallas a good 10w-30 should be fine.

Ah ok. Thought you ment for him to run 15w40. As for correct weight. What ever manufacture spec is, is what you should use. All those fancy oils out there are nothing more then a shame. Use what the manufacture calls for, unless you built your motor to different specs then you would need to figure out what kind and weight oil you need.

nlynd1978 · 11-28-2010, 02:34 PM

a cracked head would affect your compression ratio, gas millage, cooling system long before a low oil pressure issue would be seen. i hate mechanics like that. Im going to school to be a mechanic and hacks like that give us a bad name. How much oil are you using between changes and how often are you changing the oil?

dustmagnet30 · 11-28-2010, 02:42 PM

Quote:

Originally Posted by nlynd1978

a cracked head would affect your compression ratio, gas millage, cooling system long before a low oil pressure issue would be seen. i hate mechanics like that. Im going to school to be a mechanic and hacks like that give us a bad name. How much oil are you using between changes and how often are you changing the oil?

Okay...gas mileage is fine...was getting about 23-24 highway on my last trip. Yeah, I really just think he figured I knew nothing about it and would say yes to replacing the motor. I'm not the best with engines, but i'm not an idiot.

I change my oil every 3000 miles. I probably put back in a quart or so in between though.

dustmagnet30 · 11-28-2010, 02:44 PM

Also just wanted to say thanks to everybody's help. Great forum...glad I joined and look forward to many Jeep related solutions and conversations.

nlynd1978 · 11-28-2010, 02:50 PM

your changing your oil too soon unless its coming out extremely dirty or your considered an extreme service. Manufacture service interval calls for every 6,000 miles on an oil change for normal service. If your an extreme service you are fine. Jeep Grand Cherokee WJ - Maintenance information and schedules That has info on your service schedule and what type of service schedule you fit in.

Your problem is internal to the motor. Drop the oil pan, look for dirty pick up screen, oil sludge, may need to pull the oil pump and check the pressure relief valve for proper function. If its stuck open you wont build pressure.

nlynd1978 · 11-28-2010, 02:55 PM

If everything comes out good, your probably going to need the oil pump tested. Tho the least likely culprit, a worn out oil pump that doesnt flow oil at the manufacture spec rate, will cause oil pressure to be low. How ever its the least likely part to fail. Your bearings, which you need to check your clearances on both lower and upper, will fail usualy before the oil pump does. Many "bad" oil pumps are actually bad bearings. Many shops dont want to fix the cause because its less money for them vrs constantly fixing the symptoms.

dustmagnet30 · 11-28-2010, 03:08 PM

So if it's not the oil pump or the pressure relief valve, than most likely it is the bearings? Can these be replaced by access through the oil pan opening or would the engine have to be removed. What would a shop charge for that?

nlynd1978 · 11-28-2010, 03:24 PM

they can be replaced by droping the pan and leaving the motor in the vehicle, unless you need to align hone/bore the block due to extream wear. It can be pricey depending on the level of repair needed. Start with the easeier stuff first till your at the point of either the bearing or the pump.