97 XJ overheating - EVERYTHING IS NEW!!

97 XJ with 202K on it. Engine
rebuild somewhere around 120Kish....

I've replaced the rad with an all aluminum-top-of-the-line-rad, water pump, thermostat (twice), hoses (yes, spring is in the lower), thermostat housing, temp sensor, fan clutch, electric fan (and confirmed it's working), cleaned the A/C condenser, rad cap, new fluid, etc. The only thing not new is the wiring to the temp gauge and the temp gauge itself. Here is what happens.....

I can idle in 90+ degree temps with A/C on high all day long and it stays at 210 ish. As soon as I hit highway speeds (especially with the A/C on), the gauge hits about 220 then jumps to the start of the red temp (approx 250). I mean jumps like in less than 2 seconds the temp spikes. If the A/C is not on, it does not climb higher. I can detect no normal loss of power as usual when the temp start to reach critical levels. If the A/C is on and it's hot out, the temp will creep to max (about 260) on the gauge and the A/C will cut out.

Questions: Does the computer tell the A/C to cut out when the guage reads max temp? Is it possible just my guage is wrong and it's not overheating? I don't see steam / vapor come out of the hood when it's reading max temp. If I shut the A/C off and slow my speeds, within 5 minutes the temp will drop back to 220 in the same 2 seconds it took to peg.

I'm stumped. I've replaced the thermostat twice thinking it was faulty - nope. I removed the lower hose just to confirm that the spring was in place - yep. I'm out of options.

I'm figuring the guage can be bad in one of two ways.
One, the guage is reading a higher temp than actual or
Two (the worst), the temp is not registering the higher, max temp until it's too late.

Anyone have any ideas?

Do you hear/see the electric fan come on?
When the A/C is on, the e-fan should kick on too.

1. Your 97's temperature gauge gets its input from the PCM--the single sensor in the thermostat housing provides data to the PCM for engine management and the temp gauge.

2. Buy a cheap mechanical temperature gauge and plumb it in and see what it reads.

3. Contact "Ghost Hunters" care of SyFy Channel.

You should check the e-fan, but if it's overheating at highway speeds, I don't think it's the only problem.

How hot is it outside by you?

Sounds like maybe air in the system. Did you burp it? Does the level in the overflow bottle go up and down depending on hot and cold? When cold there is SOME fluid in the bottle, right?

Running lean can cause overheating. Smell your exhaust, test your O2 sensor. Any other driveability issues?

Does the cooling system hold pressure? You can rent a tester from vatozone, etc. Should hold 16lbs without leaking a bit.

A bad rad cap will not hold pressure and will cause overheating. The vatozone tester can test rad caps as well.

I like water wetter, stuff works great. Shouldn't be necessary at highway speeds though.

Your gauge (or more likely the sender) could be off.

Hm after re-reading your post, it is a stumper. The whole "it gets hotter as I go faster" is weird, usually the additional air flow at high speed masks overheating problems.

Could you have put the tstat in BACKWARDS and the water pressure at above-idle engine speed is forcing it closed? What if you just take it out

Is your belt on correctly? Spinning the water pump backwards is bound to cause issues.

I'd inspect the sending unit wiring harness for shorts or opens. Maybe it's rubbing on the firewall or something stupid like that. Heck just replace the sender, it's cheap.

Have you checked the condition of your tranny fluid?

Maybe the AC compressor is messed up and overloading the engine? You said it still overheats even without the AC though, it just takes longer? Maybe a bad bearing on the condenser or one of the other accessory pulleys?

This might be one for Car Talk...

Thanks for the input so far. I'll try and answer the questions / suggestions.....

- The E-fan is brand new and working fine (installed a temp light to confirm it's on)
- I removed the belt and checked the compressor pulley (alt is new) and there isn't any funny stuff going on (I realize bearings can be bad without noise, but unlikely)
- The T-stat will only fit in the housing one direction without hitting.
- Overall the vehicle runs excellent. No misses, stuttering and I'm getting 17+mpg with 32s so there doesn't appear to be any internal issues
- trans fluid was just replaced less than 10K miles ago
- oil looks clean
- no leaking coolant
- rad cap is brand new and not leaking. It's the pressure relief type and I popped it hot on purpose to confirm pressure - trust me, there was plenty.

How do you burp the system? This is a thought I had, but wasn't sure if it was necessary. It would make sense if an air pocket got stuck in the housing where the sensor is, but even then I find it hard to beleive coolant temperature can jump 30 deg in less than 2 seconds (honestly, 2 seconds - maybe less).

I'm going to try a new sensor tomorrow.

How would I plumb in a mechanical temp gauge?

Increased temps at highway speeds is normally indicative of a clogged radiator/obstructed coolant flow issue.

Also a sticky thermostat ... but you have replaced thermostat and radiator.

Got some details on that "top of the line" radiator ??? .. single or dual core, tube sizes etc ???

What sort of waterpump is it ... A stock type item - or some faster flow brand, that might be pushing the coolant through too fast ... and not allowing proper heat transfer ???

Coolant mix ratio .... Its only a 50% max, anti-freeze percentage ???

As suggested in other posts ... confirm your temp sensor is functioning correctly ... Recently mine was showing the actual temp of 195'f ... and then next time I looked ... It was displaying 100'f.

Cleaned / wirebrushed the sensor ... sprayed out the plug connections with electronics cleaner ... Refitted it .... and no more bouncing temps.

Sample of Hesco's: http://www.hesco.us/shop.asp?action=details&inventoryID=128580&catId=7968

summitracing.com version: http://www.summitracing.com/parts/ATM-2281/

I agree that verifying coolant temp with an infrared point and shoot thermometer pointed at the thermostat housing is a good idea.

I don't trust those infrared thermometers myself, most of them are garbage. I can shot mine at the same spot twice in a row and it will read 5, 10 degrees different. Also the sender is in the back of the head and the coolant temperature there probably is different from what it is at the tstat housing. Still, I guess that is close enough to know if you're running at 210 or 260.

I'm assuming you are running the open system with the un-pressurized overflow bottle, since it's a newer XJ. It's supposed to be self burping after a few heat/cool cycles. But sometimes it doesn't. Search for burping, plenty of writeups on here over the years.

My IR says it's only accurate within 5%, which is about as accurate as the stock display. Also, on a 97, there's no sender in the head- the single CTS for both the gauge and fan operation is in the thermostat housing.

Would have to say that overheating at high speed indicates clogged radiator, could have been debris in new unit that restricts flow. AC cutting out at high temp could be caused by AC high pressure switch de-energizing AC compressor clutch. Refrigerant pressure increases as temp goes up. Try flushing cooling system and refilling, won't cost much.

:wow:

Make sure the parts guy gave you the right water pump!!! If the water pump is turning thge wrong direction it would match your symptoms.

I like my IR thermometer gun. It is quick and easy. It is not a second gen Bureau of Standards reference, but it can damn sure tell the difference between 210* and 260*. Harbor Freight has theirs on sale right now for 26 bucks.
http://www.harborfreight.com/non-contact-laser-thermometer-96451.html

MoFo

Flow
^
|
\\ => Rotation

Rotation <= \\
................|
................V
...............Flow
Jerry_h, this idea makes sense.

sounds like you got a vapor lock going i had the same issues with my wrangler

Thanks for all the good suggestions. I guess I should have laid out a timeline for the symptoms and repairs.

When I bought the Jeep 2 years ago (25-30K miles ago), the water pump was bad. I installed a new one and it ran fine - no overheating issues over the whole summer. Last spring, I started to have issues with the temp creaping up a bit to around 220ish (previously 210-215), so I changed the thermostat and my E-fan was intermitent so I put in a new one (found out it was just the wiring) - still no major overheating. Towards the end of the summer, I started having issues with the temp creaping higher and it started to do that jump real quick to 250 thing. I replaced the rad (2 core HD alluminum) since it had over 200K on it and the alternator was original so I replaced that also - still no change. I had a winch on the front and I thought that was obstructing air flow at high speeds, so I removed it to see and still the same symptoms. By that time fall was here and with the cooler temps, I never had an issue until this spring again. This spring it seems to be even worse than last year. My power steering pump was leaking bad and groaning like an old lady so I replaced that today hoping that it may have been causing me issues. I took it for a ride and the temp creeped up, but didn't pass 220. It was only 70 here today though, so not a good test. I'll know more tomorrow.

I suppose a whole system flush isn't a bad idea. I could have a clog or something in the heater core. I suppose I could install a new high volume pump also, but I hate to start replacing items that may still be fine.

Vapor lock? I thought that was just a fuel system thing? What would cause that in a cooling system?

I had similar issues when I broke my fan shroud and didn't replace it immediately. After I got a new one it solved a lot of my overheating problems. The shroud really affects the airflow. It sounds like you probably have that covered but I didn't see it mentioned yet.

Yep, just replaced that 2 weeks ago. I couldn't believe I didn't have one on it. Didn't change my running temp one bit. I was very suprised. Good suggestion though!!