96 XJ overheats at idle with air

[Overland]

I just replaced my radiator, and I have to say the Murray I found is a lot better than the original I pulled out. My water pump has been replaced, and after replacing my fan clutch, I fixed the original and put it back in recently. I also replaced both the coolant temp sensor and the temperature sending unit. I flushed what crud there was from the block when I replaced freeze plugs a year ago. This one has the 2.5, so there is no electric fan. About the only thing I can think to do now is to replace the AC condenser, rather than try to clean the fins out on mine. As it is, I've already combed it, washed and brushed, etc. I can see through it just fine, and the air works well. As it stands, I can take 100° at 85mph with max AC and the gauge never reaches 210°. It hovers around 180-190 for the most part.

Within five minutes of idling, it's headed for the red. My four cylinder power steering system was equipped with a kicker switch, but that's been disabled to no detriment. When jumped, the idle increases noticeably, but not quite to the 1k mark I expected. Higher, smoother idle, but still having the same problem. Considering checking and cleaning the IAC port.

Any suggestions?

 

[Overland]

I suppose I should also mention that the temperature returns to normal within one mile of driving.

 

[Anak]

It sounds like your fan is not doing its job.

Any possibility that you have a fan for the wrong direction engine rotation? I know nothing about the 4 cylinders, but in '96 the 6 cylinders got a different belt routing and I believe rotation of the water pump and mechanical fan were reversed. I would look into that.

 

[Overland]

By fixed, I mean it has sheet metal screws in it, and is rigid. There was probably nothing wrong with it, but there is now. I have a new clutch in the box, but I figured direct drive would help rule it out. Also, it appears to be moving the air in the right direction.

The pump on the other hand, I have no idea. It's whatever came up at O'Reilly's, which is not always right.

 

[Overland]

The only change I can tell in four cylinder pumps is what kind of sheave drives it. All of the serpentine drive years are the same.

 

[PhotographerMike]

I also have a '96 4 cyl. w/ air. I'm guessing you have an auto trans. with 3.05 "economy" gear ratio.
( Mine is manual w/4.11, so 85 mph would be around 4000 rpm which is not pleasant. )
I'd check the fan clutch, IIRC, I had one that didn't work well.
Also, my AC sucks a huge amount of power when turned on out of the 2.5's 120 hp., but it's probably just my AC.
You can bypass the AC compressor with a shorter belt on the '96 4 cyl., I keep one handy just in case . . .

Mike

 

[Ecomike]

Get an AC gauge set on there and test the AC head pressure.

Except for your story about making it direct drive, with I would think it would eat up the pump bearings from vibration and make one hell of a racket, I would have said 99% chance it is the fan clutch, if

Is the fan shroud missing or damaged/modified?

If the head pressure is too high, like 300 psi instead of 200 psi, get a 97 parallel flow condenser and get it installed (may need fittings-tube modified? Also at idle the AC being should boost the idle speed about 150 rpm. Is that happening? If not, it is a controls issue and is not boosting the cooling as designed.

I put the 97 in my 87 Renix and my head pressure dropped from about 300 to 200 at idle on a 105 day running 1 hour at idle with out overheating (it dropped my peak coolant temp about 10-15 F), but mine is 4.0 l.

 

[old_man]

I just replaced my radiator, and I have to say the Murray I found is a lot better than the original I pulled out. My water pump has been replaced, and after replacing my fan clutch, I fixed the original and put it back in recently. I also replaced both the coolant temp sensor and the temperature sending unit. I flushed what crud there was from the block when I replaced freeze plugs a year ago. This one has the 2.5, so there is no electric fan. About the only thing I can think to do now is to replace the AC condenser, rather than try to clean the fins out on mine. As it is, I've already combed it, washed and brushed, etc. I can see through it just fine, and the air works well. As it stands, I can take 100° at 85mph with max AC and the gauge never reaches 210°. It hovers around 180-190 for the most part.

Within five minutes of idling, it's headed for the red. My four cylinder power steering system was equipped with a kicker switch, but that's been disabled to no detriment. When jumped, the idle increases noticeably, but not quite to the 1k mark I expected. Higher, smoother idle, but still having the same problem. Considering checking and cleaning the IAC port.

Any suggestions?

Does it actually boil over? Did you burp the cooling system to get out air bubbles?

Having grown up in the desert, idling an engine at 105 with the AC on full is asking a lot. While they are very loud, under those conditions I might think of converting to a flex fan, or better yet, a 4.0L radiator, shroud, and aux electric fan.

 

[Ecomike]

Interesting idea

"or better yet, a 4.0L radiator, shroud, and aux electric fan"

I wonder if the stock fan will work with that, as the fan, I think is way to right on 4.0's and closer to the center on 2.5's?

 

[Overland]

I also have a '96 4 cyl. w/ air. I'm guessing you have an auto trans. with 3.05 "economy" gear ratio.
( Mine is manual w/4.11, so 85 mph would be around 4000 rpm which is not pleasant. )
I'd check the fan clutch, IIRC, I had one that didn't work well.
Also, my AC sucks a huge amount of power when turned on out of the 2.5's 120 hp., but it's probably just my AC.
You can bypass the AC compressor with a shorter belt on the '96 4 cyl., I keep one handy just in case . . .

Mike

Nope, it's AX5. 4:10s do 70mph at about 2800 on 235/75/15s. On 265/70/17s, it's closer to 2500.

I do not intend to bypass a functional air conditioning system, or I would not have evacuated and charged it.

Does it actually boil over? Did you burp the cooling system to get out air bubbles?

Having grown up in the desert, idling an engine at 105 with the AC on full is asking a lot. While they are very loud, under those conditions I might think of converting to a flex fan, or better yet, a 4.0L radiator, shroud, and aux electric fan.

I haven't let it boil over yet, but it does head for the red in short order. If I kick the idle up with my foot to about 1400, it stays below 210. I didn't know bleeding was a thing to do on the late models, so I'll give it a try. I bled a little when I replaced the sending unit, but noticed no change. With the fan fixed, it's a little bit louder at higher revolutions, but I'm probably too deaf to notice it otherwise.

Interesting idea

"or better yet, a 4.0L radiator, shroud, and aux electric fan"

I wonder if the stock fan will work with that, as the fan, I think is way to right on 4.0's and closer to the center on 2.5's?

The core support is entirely different, the fan is centered behind a vertically oriented core, and the condenser is a different shape. I've asked this question and compared the two. For what it's worth, it's all the same for the early V6 models.

 

[Overland]

Get an AC gauge set on there and test the AC head pressure.

Except for your story about making it direct drive, with I would think it would eat up the pump bearings from vibration and make one hell of a racket, I would have said 99% chance it is the fan clutch, if

Is the fan shroud missing or damaged/modified?

If the head pressure is too high, like 300 psi instead of 200 psi, get a 97 parallel flow condenser and get it installed (may need fittings-tube modified? Also at idle the AC being should boost the idle speed about 150 rpm. Is that happening? If not, it is a controls issue and is not boosting the cooling as designed.

I put the 97 in my 87 Renix and my head pressure dropped from about 300 to 200 at idle on a 105 day running 1 hour at idle with out overheating (it dropped my peak coolant temp about 10-15 F), but mine is 4.0 l.

Fan shroud is there, all four screws, no cracks. I can hear the fan if I rev it in the driveway, but the change is almost nonexistent. Then again, I'm near deaf. Tach bumps up the width of the line when the compressor engages, but it's more pronounced when I switch the power steering pressure circuit. I just left it jumped for now.

Head pressure was high, but only a little. I adjusted the charge until I was at about 300, close enough for 100° ambient.

Going to be hot tomorrow, so I'll start at dawn with bleeding the coolant at the back of the head.

 

[Ecomike]

The core support is entirely different, the fan is centered behind a vertically oriented core, and the condenser is a different shape. I've asked this question and compared the two. For what it's worth, it's all the same for the early V6 models.

Sounds similar to my 85, 4 banger on the radiator and fan differences, and I think the grand cherokees are similar, but not likely to be interchangeable. The Grand Cherokee clutch is much better than the XJ clutch on the 4.0s, not sure about yours though.

Never had one myself, but it sounds like too little flow at idle and thus a Coolant pump impeller issue or t-Stat issue?

You mentioned idle, how low is the idle? Will it stay cool at say 200 rpm higher? If yes, I would set the throttle body for a little higher minimum idle under which the IAC can not go, if cleaning the IAC and throttle body does not help. I would not go over 900 rpm for idle.

The idle should increase on its own when the AC clutch engages. If not the ECU-IAC system is not working as designed.

 

[Overland]

The IAC compensates, but doesn't raise the idle much. The power steering pressure circuit makes a more noticeable difference. It idles a little over 600 at present. Water pump is within a year old and thermostat was late winter because I had replaced it previously with a lower opening temperature. If anything isn't flowing, it could be the condenser, being laden with bugs, rocks, and road debris, but I can still see through it, and the fins are straight.

IAC cleaning is my next project if the AC adjustment and bleeding don't do it. If cleaning doesn't help, I'm thinking about the idle stop screw.

That one you're not supposed to turn.

 

[Ecomike]

This sounds like part of the problem, "Head pressure was high, but only a little. I adjusted the charge until I was at about 300"

Mine is about 210 PSI at 105 F, but I switched to a parallel flow, new condenser to get there. 300 is too high!!!! Adds too much load to the engine running the compressor, more heat and that low RPM. 300 PSI is an indication of too much heat at the condenser and too much back pressure on the compresor and condenser. I blew my 85 (4 banger) AC condenser up running that high, 300 psi using R-134a on a 30 year old R-12 system at idle one day at 100F in the parking lot waiting..... A brand new OEM condenser and expansion valve and dryer solved the problem. I assume the condenser was the issue, but the expansion valve may have been backing up the flow or even crap in the dryer....or all three. Actually it was the pressure relief valve on the condenser that blew open IIRC..

 

[Overland]

Also, the ZJ radiator is huge in comparison.

 

[Ecomike]

The IAC compensates, but doesn't raise the idle much. The power steering pressure circuit makes a more noticeable difference. It idles a little over 600 at present. Water pump is within a year old and thermostat was late winter because I had replaced it previously with a lower opening temperature. If anything isn't flowing, it could be the condenser, being laden with bugs, rocks, and road debris, but I can still see through it, and the fins are straight.

IAC cleaning is my next project if the AC adjustment and bleeding don't do it. If cleaning doesn't help, I'm thinking about the idle stop screw.

That one you're not supposed to turn.

Idle should be at least 750 rpm as I recall, maybe uncle Bob already adjusted the idle stop LOL.

 

[Overland]

I was looking at this.

 

[Overland]

I've never seen a relief valve in an AC system, only pressure switches.

Probably why things blow.

 

[Ecomike]

Also, the ZJ radiator is huge in comparison.

I had assumed that, yes.

Since we use the MAX AC setting, that circulates 75 F air inside, I wonder if that is processing outside air to the inside or the condenser air cooling air temp or both on that data table? I do not know, we are at the point where even I would be calling the guys at Arizona Air (who told me 300 psi was too much) or asking them on their blog site for details. All I know is new parts got my 87 Wagoneer numbers down to 30/210 PSI and it keeps very cool at 105 F at about 70% humidity, or 85 F at 100% humidity and cools a hot jeep down in 2-3 minutes.

But I do also have the ZJ clutch (added later than the AC upgrades when I still had an exhaust leak blowing on the block that 3 radiator shops told me did not exist LOL.

Also that 300 PSI may be an average for all the vehicles on the road in very states of miss repair or poor design? I once thought 300 psi was normal too from those tables.

http://www.ackits.com/

They have a great blog site their tech gurus answer on for free

http://www.autoacforum.com/

 

[Ecomike]

I've never seen a relief valve in an AC system, only pressure switches.

Probably why things blow.

It was on my 85, Pioneer Cherokee, 4 banger. They used them way back, now they use a pressure switch to cycle the compressor instead (EPA R-12 Ozone regs likely forced that change). Mine was burried in the AC condenser line at the condenser, very hard to see, till it blew. Now days we have a dual pressure switch, high and low cut outs.