Engine (4.0): temp. too high, oil pressure to low. Help please

Hello.

Sorry for my English - I wouldn't ask here, but I have no place to go, not anymore. There are three or four Jeep specialists in my town and I already visited two of them - they have no idea, what's going on. My XJ is not exactly OEM, but as far as I know (I bought it not so long ago), engine wasn't modified at all.

It's '91 XJ (Mopar), 4.0, automatic. With LPG, if that matters. And I didn't change the oil yet, because the mechanic didn't have time (I am really more theoretical guy). It's 10W40 now.

First problem is that engine temperature is too high. Usually after the engine was running for a couple of miles the temperature is perfect, the gauge indicator is vertical, pointing on 100 (I don't know if US gauges are also in Celsius, sorry). But after about 15 miles of driving it jumps a bit: [ photo here ]
Usually it happens when I stop for a while with the engine on, but I'm not 100% sure it doesn't happen also when driving - I try to keep my eyes on the road mostly...
After a while it gets back to 100, but it's disturbing and everyone says it shouldn't happen.

Second thing is oil pressure. On the cold engine and for a while after it's hot, pressure is OK. But after longer drive, like 15-20 miles or so, is goes down to zero. Sometimes it jumps a little bit when I step on te gas, but not really noticeable.

Engine did about 180k miles total. It's sound is quite quiet, but it smells like oil when it heats up. The engine fan works fine and turns on at about 102 degress, the thermostat (sorry if I messed with translating those) is opening as it should, they checked it with some tool that name I cannot remember. The temperature sensor was checked and it works perfectly. The guys who are trying to diagnose it now are saying they are slowly running out of ideas. They link the pressure and temperature issues, but they don't know what exactly it is and we all think it will end up with engine swap.
Also, the interior heating is not really good, which suggests the need of cleaning something inside cooling system (as far as I understood), but nobody says it may help anyhow...

Do you think the engine is dead?

Regards.

Bumping the topic for the first and (I promise) last time - maybe someone can help...

Has the cooling system ever been flushed? If the inside heater isn't performing well, it can be from a variety of things, from blend door not operating properly to heater core clogged, to heat valve not moving.

A tick or two above 100 C isn't too bad, really. When you get to 110 C, I'd be concerned. My guess is that "normal" temp is very close to 100 C, maybe 98, which you likely can't tell on the factory gauge.

As far as the oil pressure, one rule of thumb is anything at or above 10 psi at idle is OK. Hot, at cruise RPM, I would expect about 30 psi. It might be worth it to check or change the oil pressure sending unit.

David Bricker / SYR

Does the engine make a loud clattering noise when the pressure is low?

If it's quiet at low pressure it suggests the sender is faulty.
Mopar/jeep senders are unusually the best replacement, or have the mechanic hook up a proper tester to the engine.

Overheating could easily be clogged heater core and radiator.
Hard to say based on the description. If experts are confused I'm assuming they know to check the easy fixes.

This jeep combination of motor and transmission are tough and can easily go 300,000 miles on the original motor. But if it's been abused and overheated the previous owner could have killed a very tough motor.

When in doubt go back to basics, get a oil pressure test, if it is truly low (below the standard) the motor is probably dying.
Other testing can help diagnose the condition of the motor, and there maybe other things that can fix it, the worst case scenario is following how these things usually go you may have better luck.




Sent from my iPhone using Tapatalk

The cooling issue might be the easier to tackle, although a tad over 100 is not bad. I have an '01, and I believe the electric fan kicks on at around 109, so....
Anyhow, as stated above, start with the basics. Flush the whole cooling system very good. I understand that this may invite more trouble if it hasnt been done in a very long time, but you must start somewhere. If the trouble persists, start looking at components. Hard when you do not know the history of the vehicle. The water pump may have a corroded impellor and not circulating enough water anymore. The radiator could be deteriorating or clogged, and not cooling well. Same goes for a heater system component.
As stated above, if the oil pressure at idle on a heated engine is at least 10psi, you are ok. Anything less than that and it must be investigated. I know that after I perform an oil change with a GOOD oil filter, my idle oil pressure jumps back up to about 20psi, and running pressure is around 50psi. It slowly drops as the oil gets older, to about 10psi/40psi. But zero psi is not good, replace the sending unit maybe. After that, maybe look at the oil pump to ensure that is is working and not worn.
Hope this helps.

Oil pressure: Since the oil pressure is normal except for when it has seen some driving, and seems to be related to the engine running hot, I can only think of one thing I ever found to cause that, a case just like yours that caused me no end of havoc and replacement of parts with heavy duty-better parts for years before I finally figured it out.

There were two issues. One was misfires I never heard until the spark plugs on 2 cylinders were fouled enough to be an issue. It had leaky valve stem guides on 2 cylinders that leaked oil and fouled the plugs and misfires led to thinning the oil with gasoline slowly over time. I solved the problem with NGK FR5 spark plugs that are wee bit hotter and keep the plugs clean.

The other cause was also the overheating cause. The donut seal on the exhaust manifold outlet flange gasket was leaking at higher rpms on long freeway runs, like 30 minutes, and could not be detected by three muffler shops at idle. But it was 3/4 cm from the oil pan and higher rpms it leaked hot gas onto the oil pan thinning the oil. Gasoline in the oil and hotter oil caused the idle oil pressure to drop very low, and overheating coolant combined to caused the symptoms you are having.

Are you having any other problems at all?

Your English is awesome!!!

No your engine is not dead, but you do need to find and fix the cause.

Note that mine could idle for 1 hour with the AC on and get supper hot coolant wise on a 102 C day, and the oil pressure would still be OK. At least with clean spark plugs.

I would focus on the cause of the low oil pressure. Also check to see if something is causing an issue with the oil pressure sensor wire or contacts when it gets real hot.

I did later replace my oil pump with a high flow capacity oil pump, before I discovered the real cause of the problem and I now have 291,000 miles on mine. Once I replaced the exhaust flange donut, all the problems except the fouling spark plugs went away. After about 1000 miles, if I see oil pressure dropping a little, I clean the spark spark plugs.

I plan to pull the Head and have the valve guides fixed this summer to stop the oil leaks from fouling the #1 and #2 plugs on mine. But for years I could go 5,000 to 10,000 miles before the 2 plugs got badly oil fouled.

Welcome to !!!!

Ecomike said:

Note that mine could idle for 1 hour with the AC on and get supper hot coolant wise on a 102 C day

Click to expand...

remind me never to go to Texas! 102C wow thats hot!

i think you wanted to say 102F ~ 39C :cheers:


and are you running liquid petroleum gas?

Thanks for your help, guys! I will go through your replies and translate some of automotive-specific words (i.e. "sender" - for me it's email's author!), before I consult someone here

If the problem will be solved one way or another - I'd prefer not to swap engine - I'll let you know to close this topic and provide some info for the others.

90xj06 said:

remind me never to go to Texas! 102C wow thats hot!

i think you wanted to say 102F ~ 39C :cheers:


and are you running liquid petroleum gas?

Click to expand...

No I meant the coolant never got over 102 C (I did the conversion for the OP) on days when the max here for 90 days was 105 F peak temps about 5-6 years ago. Never seen anything like it before or since.

Oh, and you past the test, LOL!!!! Go to the front of the class sir!!!!

I would look for an exhaust leak or something that is making the engine (fuel system) lean and thus getting it too hot. Or an oil pressure sensor that is going bad when it gets hot?

Also the temperature jump could just be a weak radiator cap?

Lastly, I I did install a high flow oil pump on mine (easy to do, just drop the oil pan) and I switched to 20W50 oil with 1 quart of Lucas oil. My pressure was dropping to about 8-9 psi on the hottest days after a long drive, and that combination before I found and fixed the exhaust leak got my minimum oil pressure back up to 18 psi. Now that I have the other issues dealt with (exhaust leak....) my minimum oil pressure is 28 psi.

johnporter said:

Thanks for your help, guys! I will go through your replies and translate some of automotive-specific words (i.e. "sender" - for me it's email's author!), before I consult someone here

If the problem will be solved one way or another - I'd prefer not to swap engine - I'll let you know to close this topic and provide some info for the others.

Click to expand...

Ecomike said:

I would look for an exhaust leak or something that is making the engine (fuel system) lean and thus getting it too hot.

Click to expand...

Don't forget he is running on LPG.

I would pull the spark plugs and take a look if you are running too lean. Some O2 sensors do not play well with LPG.

If the temperature is normal when you're moving and only overheats when idling check and replace the fan clutch.

Oil pressure needs to be checked with a mechanical gauge at operating temperature.

Hello.

Sorry for digging up the archaic thread, but I thought maybe someone cuold make use of my answer after googling in here. Past year I didn't drive my XJ a lot (for reasons, nevermind), but finally I got back behind wheel and went to one of the best Jeep experts in Poland.

We still didn't check yet why the oil pressure is behaving silly, but in terms of temperature, the diagnose took less than a minute - viscous fan coupling. And yes, after replacing it, the temperature is practically constant all the time.

So, @superslow, you were right

superslow said:

If the temperature is normal when you're moving and only overheats when idling check and replace the fan clutch.

Oil pressure needs to be checked with a mechanical gauge at operating temperature.

Click to expand...

My thoughts exactly.

Have you checked your oil pressure with a mechanical guage?
I just replaced my oil sender as it would drop to 0 at idle. And would pop back up when reved. With a new one that once it warms up it just drops to 0.