303XJ

Hello all, new here and with XJs so bare with me.


I have recently purchased a 2000 Cherokee with the 4.0 liter, just turned over 136,000 miles Now I have done some research and am well aware of the 0331 cylinder head issues. The oil pressure was always reading just above 10, at highway speeds and at idle. Did not fluctuate much from cold start to operating temp. This past weekend I swapped out the oil pressure sending unit, did not check with a mechanical gauge yet (that is my next plan as soon as I get my hands on one).


With the sensor swap, I am reading 40-50 on cold start, and as the car warms up it dwindles down until I am at normal operating temp and at idle it goes down to 0. I read the carfax on the vehicle and know there has been a decent amount of work performed (RMS, Oil pan, Front seal, Water pump,). There is some more work other than that as well, just figured i would list things done pertaining to my issue.


I have not seen any milkshake like oil, and my engine has no knocks or ticks, in fact it runs pretty strong. Now I know it the head is cracked, coolant can damage major engine components and allow more clearance and in return, causing low oil pressure. I have only owned the vehicle for a month, but I have noticed coolant mysteriously disappearing. I am not a mechanic, just a crazy manic when it comes to figuring out what is wrong with any vehicle I own. From all the research I have done, I have a feeling my cylinder head is cracked and could have caused damaged to my bottom end.


As I said, no knocks, no check engine light, no overheating, just oil pressure dropping low when hot, all the way just above the 0 mark at idle when the check gauges light come on. I guess my question is, is my engine doomed? I know without looking at everything in front of you its extremely hard to say. I will rebuild it I have too, but is it better to wait until I have issues with this engine? I plan to take it to a shop, but I would prefer to have an XJ expert take a peek.


Please feel free to ask any questions, or tear me apart for buying a lemon (haha). Just need some advice really, because I want to keep this thing on the road for years to come.

jpz

At this point, (like you said) you need to verify the oil pressure with a mechanical gauge. Anything else you do, is just throwing money away.

Also, if you are losing coolant and continuing to drive it you are lessening your odds of saving the engine in the event the head is cracked and that's where the coolant is going.

My XJ had the head crack around the 50k mile mark, but the loss of coolant was immediately caught, head was replaced with a TUPY head and I now sit at 150k miles and still have a good 13 or so PSI at hot idle. So an engine can be saved if caught in time. It can also be destroyed if ignored.

Time to do some troubleshooting.

303XJ

So just because my oil pressure has dropped, doesn’t automatically mean I have engine damage? I just figured the damage had been done and a rebuild was most likely in my future. But thank you for the advice, I am in the process of finding a mechanic who is well versed with the 4.0 and has a knowledge of what to look for when it comes to the 0331 head.

robsjeep

1... You need to confirm what the pressure really is, thus test with a known good gage. If indeed low, it needs to be repaired, it maybe as simple as the wrong oil is being used, it could be the engine is running too hot, these things can give low pressure when mechanically speaking, the oil system and bearings are fine. maybe the pump inlet screen is blocked, or pump is bad, pick up tube leak, low oil level, or worn out bearings, or you got coolant in there, etc....

Continued driving with low pressure will damage engine parts which may still be fine as of now.

2. Coolant loss needs to addressed, if it is the cracked head issue or any other leak into the engine of coolant, it needs to fix before you drive more, as coolant in the engine (other than in the cooling system) will damage the motor. coolant loss may also be external to engine, hoses, pump shaft seal, pressure cap, etc...

good luck

jpz

You don't necessarily need a mechanic that has knowledge of the 4.0 and 0331 head. There is countless pics, and videos on the internet of what to look for.

The 2 biggest things you need to do is get a mechanical gauge on there to verify what the actual oil pressure is and figure out what is going on with the coolant loss.

You may get lucky and find that your in dash gauge is wrong, and that your coolant is leaking somewhere.

You may get unlucky and find that your in dash gauge is correct, and that your head has been cracked and letting coolant into the oil.

But until then, it's just guesswork that could end up costing you more money than it should.

303XJ

Thanks for the advice guys. I got an appointment set up to bring it into a shop. They are aware of my concerns, and I will post results once they follow up.

robsjeep

low oil pressure may result if someone put in the modern techie new fangled "fuel saving" thin oils such as 0w-10, which should never be used in the jeep ( unless maybe it is used at the South Pole during winter!)
I am not saying an oil change is the first thing to do, but you should inspect the oil. Do at room temp, compare how it drips off the dip stick, how thick it feels when rubbed between fingers verses how the correct oil is. Make sure test is done with both oils at same temperature after taking a dip stick sample of your engine oil, wipe dipstick clean and use dip stick to obtain oil from the correct oil bottle. note how the oils flow on the dip stick, feel the oils. so buy a bottle of the correct (summer grade) oil and compare side by side, if what is in your engine is thinner, then change it to the correct grade oil. I hope that is your issue, easy peasy, who knows what oil prior owner put in there?

303XJ

I guess I left that info out, my bad! I actually just changed it with valvoline 10W-30 and had a valvoline oil filter put on. I have also read of people using 10W-40 to help with pressure. I know 10W-30 is standard, I guess what would be the next best option for thicker oil?

robsjeep

Thicker oil can help, but Id not go spending on another oil change yet, as your current oil is fresh, and should be ok, id look into getting a known good gage, cause maybe the pressure is fine.
Oh also make sure the oil does not smell of gasoline, sniff the dip stick. If it does smell of gasoline, then you got a leaky injector(s), or the system is directing an over rich mixture to your engine. Too much unburnt gasoline will contaminate the oil, as the unburnt fuel in the cylinder and it makes it way past the rings into the crank case. thins down the oil, and causes low oil pressure. Give it the ole smell test. Yes a leaky injector can cause low oil pressure do to thinning of the oil.

by the way, rule of thumb for gasoline car engines is when fully warmed up, about 10 psi of oil pressure for every 1000 rpm of speed minimum. 3000 rpms and you should be having at least about 30 psi. A new engine should be more, to allow for pressure drops do to eventual wear. Below that pressure by much and you risk not having enough pressure to maintain a complete oil film which is supposed to separate the bearings from the spinning shafts, high rpms require more pressure as the higher speed tends to pull and stretch that oil film thin. If that film goes away, that is when metal to metal contact and high wear occurs.