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Cooling system driving me crazy

Take a good look at your fan clutch, you may have replaced it but "their not all created equal".

I would think that the mechanical fan would be most helpful in city driving and if my clutch was indeed going bad it would be evident with my electric fan having to kick on while idling/city driving. I will take a look at it but even if it wasnt working 100%, with the airflow I "should" be getting on the highway it shouldnt make a difference.

Not sure about next steps, maybe a compression test, a thermostat swap (just in case it does not actually fully open enough for highway demand), and an IR gun to monitor temperatures (lower vs upper radiator hose, thermostat housing, front vs back of head, etc...).
 
i was watching your mpg thread,

you say you were fine while you were in CA, but have problems now, did you increase your tire size since then?

also do you have any exhaust leaks in your manifold?

mine is doing the same as yours, i know i have an exhaust leak, and i know i have the wrong gearing, no AC i can run all day long, if i have the AC on my temps climb, i was wondering if it was my transmission temps, but yours is a standard, so maybe we have the same issues, just thinking out loud here
 
i was watching your mpg thread,

you say you were fine while you were in CA, but have problems now, did you increase your tire size since then?

also do you have any exhaust leaks in your manifold?

mine is doing the same as yours, i know i have an exhaust leak, and i know i have the wrong gearing, no AC i can run all day long, if i have the AC on my temps climb, i was wondering if it was my transmission temps, but yours is a standard, so maybe we have the same issues, just thinking out loud here

Tire size has not changed. Im not entirely sure about exhaust manifold leaks I just always assumed mine was leaking and was planning on doing a complete exhaust overhaul (headers, high flow cat, and my existing cherrybomb) but dont have the cash for it just yet.

The exhaust system, tire size, and gearing has been the same since before this highway overheating problem started. Mine overheats on the highway regardless of AC being on or off. Not exactly sure how to go about this, I will test today on my way back from work after yesterday passing pressure test (only dropping 1.5-2 psi in 20 min), block test (no color change at all), and new radiator cap. If it still overheats, I might go ahead and replace both coolant temp sensors (one in housing and on in the back of the head), I might also pull my existing thermostat and test it (although im pretty certain it opens and closes) but maybe, and thats pushing it a bit, maybe it doenst open all the way to allow for highway flow demand. If all this checks out and doesnt solve my issue, im going to do a compression test and perhaps an IR gun to verify temps and check for radiator blockage (although replacing both coolant temp sensors should fix it if I have a sensor/gauge issue, which I doubt as the gauge works as expected and doesnt make weird movements or give out weird temps)

hopefully we can get this fixed man, it sucks when you cant even identify the problem and just have to pull the parts trigger and start throwing parts at it until it works..

If anyone has any suggestions please let me know, I really want to know whats causing it and fix this
 
SEXJ96,

I've been re-reading your posts to help with a fix. I have CSF radiators and have had no problems with them. But, I've noticed a recent trend in cooler designs that may or may not be the issue with your new CSF radiator. The "trend is to increase the fluid flow velocity (i.e. increase Reynolds Number) to increase the heat-transfer. This is done by reducing the cross-sectional flow areas and allows the manufacturer to build smaller radiators with less material. This technique is used to design compact coolers for aircraft. Unfortunately, these small flow passages in the radiator/cooler can clog faster. Likewise, "rodding" (i.e. unsoldering the top/bottom of the radiator and running a rod through each core tube to mechanically remove scale) is impossible with these types of radiators. Chemical cleaning is the only way to unclog these units. At this point, if it were my XJ I'd get another radiator from a friend or one from the junk yard and swap it for the new CSF and see if it cools any better. Some of the tubes in the CSF radiator may have clogged and simply not cooling your XJ enough.

Best regards,

CJR
 
Just an FYI,....the water to the in cabin heater by-passes the thermostat goes through the heater core then returns to the engine via the water pump.

In addition to air flow through the radiator, look at/replace the thermostat. I use only thermostats sold at the Jeep dealer. It have the air bleed hole in it already and a little jiggle valve installed. Others here on the NAXJA forum have had good luck with other brands.
 
Buy an ir temp gun.theyre cheap and you can 1: check the actual temp compared at least to your gauge and 2: check your radiator. Move up down and across with it running at operating temp. Any sudden. Cold spots or jumps in temp indicates a clog.

https://www.amazon.com/Innovative-Products-America-8052-Cleaner/dp/B005MVB4D4
I keep one of these at work. As Ong as you have a compressor they work awesome for cleaning radiators and condensers.
 
SEXJ96,

I've been re-reading your posts to help with a fix. I have CSF radiators and have had no problems with them. But, I've noticed a recent trend in cooler designs that may or may not be the issue with your new CSF radiator. The "trend is to increase the fluid flow velocity (i.e. increase Reynolds Number) to increase the heat-transfer. This is done by reducing the cross-sectional flow areas and allows the manufacturer to build smaller radiators with less material. This technique is used to design compact coolers for aircraft. Unfortunately, these small flow passages in the radiator/cooler can clog faster. Likewise, "rodding" (i.e. unsoldering the top/bottom of the radiator and running a rod through each core tube to mechanically remove scale) is impossible with these types of radiators. Chemical cleaning is the only way to unclog these units. At this point, if it were my XJ I'd get another radiator from a friend or one from the junk yard and swap it for the new CSF and see if it cools any better. Some of the tubes in the CSF radiator may have clogged and simply not cooling your XJ enough.

Best regards,

CJR

Thank you, I did not know they did that! Increasing reynolds number makes sense but decreasing the cross sectional areas is a big no no, especially with older cars where gunk, debris, loose particles, etc... are more common. I was thinking of replacing a radiator with another one just to eliminate it being the problem for sure but instead of actually having to replace it I could eliminate it with an IR temp gun and possible feeling for cold and hot spots on the radiator itself. Thank you so much!

Just an FYI,....the water to the in cabin heater by-passes the thermostat goes through the heater core then returns to the engine via the water pump.

In addition to air flow through the radiator, look at/replace the thermostat. I use only thermostats sold at the Jeep dealer. It have the air bleed hole in it already and a little jiggle valve installed. Others here on the NAXJA forum have had good luck with other brands.

I checked yesterday and I do have a heater control valve, Ive never had issues with it and heat in the cabin is great when I need it. Maybe my heater core is blocked slightly to the point where its impeding flow for highway speeds. I will try flushing it separately and see what comes out and how the flow is. I have a Stant on there now and I can verify that it opens up and closes by 1) seeing the water level drop in the radiator neck as soon as it gets to operating temperature and 2) increased pressure in the upper radiator hose. I will try replacing/testing it just to completely eliminate it being the issue.

Buy an ir temp gun.theyre cheap and you can 1: check the actual temp compared at least to your gauge and 2: check your radiator. Move up down and across with it running at operating temp. Any sudden. Cold spots or jumps in temp indicates a clog.

https://www.amazon.com/Innovative-Products-America-8052-Cleaner/dp/B005MVB4D4
I keep one of these at work. As Ong as you have a compressor they work awesome for cleaning radiators and condensers.

Unfortunately, I do not have access to compressed air at that pressure. I will get an IR temp gun and check the temperatures. Thank you!

**Updates:

Yesterday on my way back from work, the AC was on and I was doing around 65-70 mph on the highway in 4th gear and rpm was around 2200. The temperature started going up and I wanted to see if it stops climbing so I did not do the usual (turning AC off, heater on, decrease speed) instead I kept going with AC running and everything and it kept going up, once it went a little bit past the 3/4 line and before it hit the red zone I pulled over. Radiator cap was hot, upper radiator hose was hot along its whole length and pressure was rock solid. No visible leaks, no boiling over into radiator overflow bottle, and I also noticed that the overflow bottle's level had decreased from the full mark to slightly over the add mark. I turned the AC off and the electric fan kept running, I turned heater on and gave it a little bit of gas in neutral and the temp started dropping instantly. I found a temperature vs resistance table for the coolant temp sensors and sending unit so I wanted to test mine. I started with the sender unit since the fan turns on when its supposed to so I figured nothing is wrong with the sensor.

As soon as I tried pulling the plug off the sender unit, without any excessive force, the sender's white plastic casing broke apart and the plug came off with the top part of the sensor. The only thing left was the brass nut and threads. I took a good look at it and guess what? It was stripped. Not completely but the outer edge was rounded off pretty bad. I tried getting a socket on there but it wouldnt sit due to the valve cover being so close. It seemed like a 1/2" wrench would fit but I could only get the open end on it and I didnt want to strip it worse. I tried a vice grip, channel locks, and cresent wrench and I could not get enough leverage/space to turn it. The vice grip damaged it pretty bad and I ended up hammering a 12mm socket over it and since it was smaller than the nut it cleared the valve cover. That got it out. Unfortunately, advanced needed to order the part from another store as they didnt have it in stock, they only had the sensor so I am waiting to get off work today and get the part and plug it back in. Im hoping that since it was in such bad shape, it was mis-reading temperatures or ambient (under hood) temperature had an effect on its readings. I will also take the car to a car wash today and use the power washer to wash the condensor/radiator from all the crap that might be stuck in them. Im not sure whether to go outside to inside or inside to outside. Inside to outside makes more sense to me but Im not sure if thats possible with everything on the car.

Let me know what you guys think!

Thank you,
Laith
 
I think that basic testing and basic cooling maintenance for ALL of the cooling system parts needs to be completed before you start worrying about potential/theroretical internal mechanical issues. You need accurate data to diagnose.

I disagree with the way Tim_MN phrased that. The way that the OP responded to that post proves my point. It leads to optimism that can blind you.
Replacing components like the fan clutch, thermostat, rad hoses, electric fan, coolant, etc. will NOT fix a blown head gasket or cracked block. Those "potential/theoretical" failures will not go away on their own, and you'll waste money replacing good parts around them trying to make it go away.

Disclaimer: Cooling system maintenance IS important, and replacing old parts is OK.

BUT FIRST, test the big items like rad pressure test, hot compression test, hot block test (like overheating level hot).

This has been a really hot year, and it seems to be killing the late 90's 4.0l's. See recent posts, including one where my head gasket was blown that was only proven by block testing when the engine was getting to overheating range: https://www.naxja.org/forum/showthread.php?t=1149596&page=2

Best of luck!
 
I hate to tell you this but I was chasing the exact same problems. I replaced everything in the cooling system except the radiator because it was not very old. Well guess what I replaced it with a cheap parts,store 1193 radiator and now I cant even get it up to 210. So in my case I guess the problem was obvious .
Good luck
 
To SEXJ96,

Let me be very clear. Your problem is not the heater core. If it was, two things would have been different,...
1) The heat in the cabin would have been low or non existent.
2) Having the coolant circulate through that small heater with the in-cabin fan blowing over it would have had no effect on the high coolant temperatures.

Your cooling problems lie somewhere outside the cabin heater. Thank goodness for a good heater. It have saved my 1994 4.0 on a trip from Connecticut to Kansas in 2001 with no machinal fan. There was the older style electric fan and nothing where the mechanical fan should be.
 
That's why IR guns are valuable tools.

Yes they are indeed.

I disagree with the way Tim_MN phrased that. The way that the OP responded to that post proves my point. It leads to optimism that can blind you.
Replacing components like the fan clutch, thermostat, rad hoses, electric fan, coolant, etc. will NOT fix a blown head gasket or cracked block. Those "potential/theoretical" failures will not go away on their own, and you'll waste money replacing good parts around them trying to make it go away.

Disclaimer: Cooling system maintenance IS important, and replacing old parts is OK.

BUT FIRST, test the big items like rad pressure test, hot compression test, hot block test (like overheating level hot).

This has been a really hot year, and it seems to be killing the late 90's 4.0l's. See recent posts, including one where my head gasket was blown that was only proven by block testing when the engine was getting to overheating range: https://www.naxja.org/forum/showthread.php?t=1149596&page=2

Best of luck!

Exactly. So based on what you said I block tested it with the temperature close to 3/4 mark and the test came out negative (i.e fluid stayed blue). I thought I messed it up and tested it again, still negative. Updated is below in this reply.

I hate to tell you this but I was chasing the exact same problems. I replaced everything in the cooling system except the radiator because it was not very old. Well guess what I replaced it with a cheap parts,store 1193 radiator and now I cant even get it up to 210. So in my case I guess the problem was obvious .
Good luck

At this point, I hope it’s a radiator and not something bigger. I would rather verify my radiator and it’s effort to cool coolant with an IR temp gun rather than replace it and see what happens. Hopefully the temperature values would indicate something instead of being inconclusive.

To SEXJ96,

Let me be very clear. Your problem is not the heater core. If it was, two things would have been different,...
1) The heat in the cabin would have been low or non existent.
2) Having the coolant circulate through that small heater with the in-cabin fan blowing over it would have had no effect on the high coolant temperatures.

Your cooling problems lie somewhere outside the cabin heater. Thank goodness for a good heater. It have saved my 1994 4.0 on a trip from Connecticut to Kansas in 2001 with no machinal fan. There was the older style electric fan and nothing where the mechanical fan should be.

My old man suggested a blocked heater core the other day when I was talking to him about this and my reply was the same thing you just said. Given I’m getting hot air out my vents and my temperature significantly drops when I turn the heater on then it should be fine.

**Updates:

So I replaced the coolant temperature sender unit and I had a hard time getting it tight all the way (stubby wrenche, deep socket, etc...did not work) so I bought some crowfoot wrenches and got it down all the way. The temperature gauge reads the same, around halfway (+- a little bit) with or without AC city driving but at highway speeds temperature climbs to 3/4 mark. Maybe the sensor shows temperature changes faster (i.e when I turn heater on and decrease speed and give it some gas in neutral) but that might just be placebo effect lol

I power washed the condenser and radiator while they were still on the car, no major mud/dirt fell but they look cleaner. Still did not test if after power washing them. However, I noticed my coolant reservoir’s level had decreased. I’m assuming I now have some air due to the fact that the sender unit was out overnight until I got the new on in. But just to be sure, I pressure tested my coolant system and it only dropped around 0.5 psi in an hour and 20 minutes. Just a quick question if anyone knows, theoretically even if the thermostat was closed when I pressure test the system I am also pressurizing the block (water jackets) correct? I’m thinking due to the fact that the pump has no valve then I would be pressurizing everything from both ends of the thermostat, inner and outer correct?

My next steps would be to try and get all the air out. I will keep filling reservoir and heat then cool it to have it suck all the coolant it needs. Any other way of doing this? I would rather not open the cap and run the engine until thermostat opens then fill with coolant as before the thermostat opens With the cap off, I have coolant overflowing from the cap (I’m assuming due to back pressure of the pump) and then I wouldn’t know if I’m filling the coolant than overflowed or the coolant needs due to air escaping....

Next up is a IR temp gun verification and maybe a compression test. Let me know what you guys think or if you have any suggestions.


Thank you,
Laith
 
Assuming the IR temperature check of the radiator checks out OK, I would guess you may have a blockage somewhere in the head or block. Maybe a piece of internal casting slag that's broken off and blocking some coolant passageways. Not a good thing! For me that would dictate pulling the head and maybe the engine block for pressure testing, chemical cooking-out, extreme flushing-out, magna-fluxing for cracks,etc. A real PITA!

Best regards,

CJR
 
I disagree with the way Tim_MN phrased that. The way that the OP responded to that post proves my point. It leads to optimism that can blind you.
Replacing components like the fan clutch, thermostat, rad hoses, electric fan, coolant, etc. will NOT fix a blown head gasket or cracked block. Those "potential/theoretical" failures will not go away on their own, and you'll waste money replacing good parts around them trying to make it go away.

Disclaimer: Cooling system maintenance IS important, and replacing old parts is OK.

BUT FIRST, test the big items like rad pressure test, hot compression test, hot block test (like overheating level hot).

This has been a really hot year, and it seems to be killing the late 90's 4.0l's. See recent posts, including one where my head gasket was blown that was only proven by block testing when the engine was getting to overheating range: https://www.naxja.org/forum/showthread.php?t=1149596&page=2

Best of luck!

I agree with Tim. Keep it simple and test the most common stuff first.

Head gasket, cracked head/block are very rare.
 
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