Phil_XJ

My ’93 XJ 2.5L Manual trans is having overheating issues, has 163xxx on odo. Here is the background.


Bought it, ran fine, but got up to freeway speed and it ran a little warm about 220-230 (I was able to go about 25 miles on the freeway without it getting hotter than that), and as soon as I would get down to street speed it would go back to 210. Now at street speed it will start to overheat if I'm going too long. It has gotten up to halfway between 210 and the next mark on the gauge, same as freeway. I haven’t pushed it too hard to see if it will go hotter than that but it seems to stay around there.

I drove with fan off (switch inside) and let it run to about 220, then turned it back on and idled for about 15 minutes. Quickly dropped to about 205 and stayed there the whole time.

Here’s what I have tested or replaced, I am hoping for a little help diagnosing this.

Radiator cap – replaced.
Thermostat and thermostat housing and gasket – replaced. Failsafe thermostat, will fail in the open position if it fails, but I know that it is working.
Radiator Fan/ Fan Clutch/ Fan Shroud – all working perfectly fine, wired to a switch inside the cab so I can control it.
Radiator – I suspected the radiator and I heard they get clogged often, so I used a temp gun on it to look for “cold spots” and it seemed to be perfectly free of any clogs, it was pretty much the same temperature horizontally and hotter at the top and about 15 degrees cooler at the bottom. I checked the temperature the whole time it was running from cold start to 210. Does not seem to need replacement.
Hoses – all in good shape, and no clogs detected from temp gun or when hand checked at cold
Water Pump – I am not leaking any coolant anywhere, and not making any noises. Does not seem to need replacement.

I have read that often head gasket failures cause overheating. When I changed the thermostat almost two months ago I drained all coolant, there was no discoloration or oil in there. There is also no white smoke from my exhaust, or any smoke for that matter. Another test I read is to open the radiator cap when it’s cool, and run the engine and check for bubbles (cylinder compression being pushed into the cooling system), and there are no bubbles. I think a head gasket issue is unlikely. Just looked again first thing in this morning, it’s just as full as I left it 2 months ago and just as yellow/green as it was straight out of the bottle.

I have seen people have all sorts of upgrades to their 4.0L that I would love to do but I don’t think they will work on my engine. There is no CSF 2 or 3 row metal radiator option for me, and I doubt a grand Cherokee fan clutch will fit in mine. I’m at a loss for what to do.

Any ideas on what might be causing this to overheat? And are there are cooling upgrades that work for the 2.5L engine?

jakbob

i thought the 2.5 had a single viscous clutch fan on the front? if you have an electric AND a mechanical, i suspect the mechanical clutch.

djb383

A wild guess would be an old radiator, how old is it?......the temp gun says it's heating up evenly but it won't tell u if it's shedding/loosing heat efficiently. If the rad doesn't shed/loose/remove heat from the coolant, motor will run hot. This water pump didn't leak either. LOL

askingxforxit

Don't rule out your water pump. Mine wasnt leaking either but on the streets the jeep ran a, little warm and at a stop it would reach about 220°F. I have a '00 4.0 we replaced the water pump the other day and this is what I discovered.



Now my temps don't go above 212° on the street in 95+ temps with AC on full blast

Phil_XJ

Alright cool. Sounds like it'll be worth pulling the water pump off and having a look this weekend. I'll post when it's done and let you know, thanks for the input. I didn't realize they could look that bad inside without showing external signs!

djb383

It's amazing how easy the old rad comes out and a new 1 goes in while the water pump and t-stat are removed.....and when all 3 are done at the same time, u only have to drain/refill coolant once. Best way to flush the head/block is thru the t-stat hole and out the pump hole.

Phil_XJ

Sorry it's been a couple weeks - haven't gotten the water pump off yet. I'm saving a little for a high-flow hesco one because they look awesome and I want to be able to rule out the water pump issue altogether. Two quick questions though

1. If i get the Hesco pump will it require me to get the high flow thermostat housing as well or can i just use the new one I got from o'reilly that's already on there?

2. I checked the sending unit to the gauge on the engine, the brass sensor in the rear of the engine, and it read a lot higher than the gauge did with my temp gun. The gauge said just shy of 210, and the outside of the block next to the sensor read about 190 and the brass sensor itself was about 240. Is that normal? I thought that the temperature of the sensor would match with the gauge.

Phil_XJ

Does this sound like a bad water pump? (Link below) Sounds like a diesel engine kind of. It's done this since I bought it and my friend's did this too, so I figured it was just the normal engine sound.

http://www.youtube.com/watch?v=LsZxD...ature=youtu.be

djb383

Sounds like an exhaust leak.....kinda hard to diagnose over the internet. How's the replacement of the cooling system coming?

I believe the brass sending unit is in the head, not the block.....are u sure u didn't accidentally get a temp gun reading (240) at an exhaust port vs the temp gauge sending unit?

Phil_XJ

It's not an exhaust leak, I don't mean the blowing sound near the end I just mean the running noise that sounds diesely. It might just be normal I'm not sure how quiet these are supposed to be. The blowing is my fan.

It is going slow. Almost nothing done haha. I only drive a mile to and from work so I've been putting it off but it's time where I can't anymore because I'll be driving farther. Basically it's been getting hotter, and that peak temperature it always hits and stops at keeps getting higher and higher over time.. Then again so do the summer temps here in AZ. I'm going to replace the pump in the next couple days, or this weekend worst case. Just wanted to see if anyone recognized the noise as the same problem.