Running hot and oil pressure

[Virginia]

My oil pressure has been running around 20 when the engine is fully warm and yesterday the temp guage went up to right at the red zone. I checked the oil and found it was low so I added. I also added water to the overflow because that was totally dry. I'll see what the temp runs to day but am more worried about the oil pressure.

 

Is 20 normal?

[Eagle]

At what engine speed are you seeing 20 psi? The factory spec is 13 psi minimum at 650 RPM idle, and 37 to 75 psi above 1300 RPM. Most XJ and MJ engines seem to idle in the 20 to 30 psi range and run about 50 psi at highway speed. If you are seeing 20 psi at idle, you're good to go. If you're seeing 20 psi while moving, when the RPMs are above 1000, that's not normal.

[jimoshel]

20psi on a very high mileage engine is normal. It's also a warning that you don't want to be hard working or high revving the engine until you drop the pan and replace the bearings.

[Virginia]

I'm seeing 20 at about 2000 RPM's. I believe it used to run close to 40 at 2000 rpms.

 

I've never changed the bearings. Is that hard?

When I turned off the engine, I could hear the coolant bubbling and could see it bubbling back into the expansion tank. I took the radiator cover off and saw what appeared to me to be mud. It was brown and looked like that really slick pond mud. It sounds like I'm suddenly having multiple issues. The oil pressure started suddenly and so did the hot engine. Should I flush the coolant? Change the thermostat? And do what about the oil?

[mvusse]

Did you add tap water, or distilled water?

 

(Even moderately) hard tap water has iron in it. That iron will turn to rust and stick together to form what looks deceptively like mud. And it is REALLY good at clogging radiators. Flushing the cooling system would definitely my first step.

 

Is the oil pressure always that low, or is it fine for a few days after an oil change? When my injectors were leaking some of the excess gasoline would work past the piston rings and end up in the oil. Oil pressure was fine after an oil change, two months later while wheeling I had 0 pressure while idling, ~20psi when revving it up. Changed the oil and all was fine again. The old oil was water thin. Problem has now been permanently solved by a new set of (rebuilt) better injectors.

[Incommando]

Related issue:

 

On my '88- It rattles very badly for a second or two after firing if it has sat even for a few minutes. Shutting it off and re-firing in just a few seconds prevents iy. Putting a Wix filter on it helped some. The PO had just replaced the rear main seal.The idiot light appears to work correctly.

 

The engne rattles ( more like valvetrain ) at higher RPM's or when nailing it when warm. It runs strong, though.

 

Idears?

[Virginia]

Oil change doesn't make a difference. When I first crank it and it's cold the pressure is up around 60 then it slowly drops to 20 as the engine warms up.

 

This is the first time I've put water in it since I had the radiator rodded about 7 years ago. I don't know what was used the last time I had it flushed which was just about that long ago as well. I know, way too long for that to be done. I'll have it flushed tomorrow.

 

I am getting some rattle when I accelerate hard like on the interstate on ramp or having to pass someone and that rattle is new.

[Virginia]

More info...the radiator cap was cool but the top hose and the radiator was hot. I turned on the heater and it was blowing cold air while the temp guage was showing the needle right next to the red zone. As the needle moved down, the air began to get hot coming out of the heater.

 

How do I know if the water is low in the the cooling system?

[Pete M]

if you have access to an inferred thermometer they are a great way to track the heat (or lack thereof) in a cooling system. :thumbsup:

 

 

could be that you have an air pocket in your engine that needs to be burped out. but more important, you need to find where that coolant has gone. any evidence of leakage? under the waterpump? under the rad hoses? heater box? (probably the worst case scenario)

[Virginia]

I can't find any evidence of where it went. I've seen no leakage. I added about a gallon of water to it. I also changed the plugs which was way over due. Right after that, my oil pressure was back where it should be and the temp gauge register exactly where it should.

 

I have no idea if those are connected but it sure seems to be doing fine now. Changing the plugs stopped the missing that I was feeling also.

[1987Comanche]

On my '88- It rattles very badly for a second or two after firing if it has sat even for a few minutes. Shutting it off and re-firing in just a few seconds prevents iy. Putting a Wix filter on it helped some.

 

My '90 would make some scary cold start noises, espec when it got below 30 outside. Retrofitting the later model, horizontal mount oil filter made a big difference.