4.0 - replaced entire cooling system, still overheating

Hey all - I have a lengthy thread on CF.com about this but it seems to have run its course and a cross-post can't hurt.

95 4.0 5-speed on 35s/4.88s with a motor from a 97; it idles fine but temp likes to live just to the right of 210, but when I'm at 50MPH or faster, it gets up to 230-235 or so, and under load gets there quickly. It really wasn't an issue in the cooler months but now it really is.

I've replaced literally everything. Here's my list so far:

New:
Factory thermostat (tested, opened at 195)
Thermostat housing
Napa fan clutch
Spectra radiator
Hoses
Water pump
Radiator cap
Temp sending unit

I flushed the system and heater core multiple times. I did a compression test and everything was within spec, and I also tested for exhaust in the coolant and found nothing. What on earth could still be causing this??

Sure appreciate any advice!

What method was used to test for exhaust in the coolant?

I just had a customer have similar issues ( higher cruising temps than yours) and his issue was caused by a reverse rotation water pump. No external difference between the 2 pumps could be seen.

I bought the kit with the blue liquid and it sure seemed to stay the same color. During the compression test I forgot to wedge the throttle open and everything was already between 150-120, so numbers probably would have been even higher.

So it's been a while since I put the new water pump in, but I did make sure the new one looked like the old. Turns out I still have the old one out back, and it seems to be correct:



I don't suppose there's any way to test whether it's the correct rotation without taking it off again??

I've still got the NAPA order in my email, it was NAPA 42004 - says "reverse" under rotation. But since I have no idea what else it could be, maybe either my new water pump or new fan clutch is bad. I did buy a fan clutch for a Grand Cherokee but I just couldn't stand how loud it was.......maybe it's worth fooling with getting that thing back on there just to see if it cools properly?? Maybe then I'd know if the new fan clutch is the issue.....sigh

Unfortunately, no one really knows why these jeeps tend to have overheating problems. I've probably read every thread/article on the internet about XJ overheating issues, and no one has ever pointed to a specific solution. It seems the answer is always to throw different parts at it until something works, or you just put up with it.

I've dicked around with 4 XJ's, (still own them all), and each has had their own challenges. I've literally tried 6 different radiators, different water pumps, thermostats, flushing, changing the cat/exhaust, different thermostat housings, different fan clutches, Everything. Some with more success than others.

The only one without any major issues is my son's bone stock 99. But he temp will still creep on long freeway uphills in the summer time with the a/c running. The other 3 are trail rigs with varying degrees of pain-in-the-assness, when it comes to cooling.

Honestly, the best thing I've found is to put in an e-fan over-ride switch and use that to mitigate any temp creep. My chemist brother in law thinks it's mostly an air flow issue with XJ's.

So, you'll probably be like everyone else, throw parts at it and hopefully something will work, or get frustrated and put up with what you can. No one knows a solution.

The efan should kick on at 220-222F. Coolant temp is probably holding at 220-225F with the vehicle stopped and engine idling because of the efan. Does it hold at 220-225F with the A/C running with the vehicle stopped and engine idling or does it creep up further?

Here are some things to consider although I don't think that any of these are the solution for your situation:

- The late model efans flow much more air the the early model. The TYC fan on Amazon is a good one.
- Did you regear for the big tires? Remember that mechanical fan speed will scale with engine rpm, so if you are on 33's with stock gears, there's going to be a tendency to lug the vehicle around at lower rpms where mech fan speed will be lower.
- Make sure the A/C condenser is clean and has straight fins.
- Winches and bumper light bars will affect air flow to the radiator.

The temperatures you are seeing suggest a bigger issue such as:

- Water pump not functioning properly.
- Slightly blown HG.
- Clogged cat.

All those would contribute to higher coolant temp on the highway.

Since you have flushed it multiple times I'm going to hazard that you have broken loose scale out of the system and re-clogged the radiator. Happened to me when I reversed the flow in my heater core. No amount of flushing back and forth could get me any heat, so I did the old school trick of switching the hoses. Finally got my heat, but then led to over heating when ambient was higher. The scale that broke loose clogged up a 6 month old radiator that the system had been flushed on upon installation.

Thetastycat said:

Hey all - I have a lengthy thread on CF.com about this but it seems to have run its course and a cross-post can't hurt.

95 4.0 5-speed on 35s/4.88s with a motor from a 97; it idles fine but temp likes to live just to the right of 210, but when I'm at 50MPH or faster, it gets up to 230-235 or so, and under load gets there quickly. It really wasn't an issue in the cooler months but now it really is.

I've replaced literally everything. Here's my list so far:

New:
Factory thermostat (tested, opened at 195)
Thermostat housing
Napa fan clutch
Spectra radiator
Hoses
Water pump
Radiator cap
Temp sending unit

I flushed the system and heater core multiple times. I did a compression test and everything was within spec, and I also tested for exhaust in the coolant and found nothing. What on earth could still be causing this??

Sure appreciate any advice!

Click to expand...

I am going through the same EXACT thing and it doesn't make any sense! In addition to what you have done, I recently installed a stand alone trans cooler (no difference).

One of my good friends believes that by lifting my Jeep (4" IRO lift and 33's) I have altered the air flow at highway speeds and that an air dam would help more air flow through the radiator. Thoughts?

Anyways, my next step is to replace stock clutch fan with an electric fan, and Mishimoto aluminum radiator if that fails.

Hey all - thanks for the great ideas. Max, good thoughts on the efan - let me confirm that mine is working properly, though it was the last time I checked. I did regear to 4.88s for the 35s, and I understand that's more work for the motor, but something else is going on for sure. No idea on the condenser - will definitely have a look!! I do have a winch but still should be working OK.

So MAJOR update - I found a fantastic list here of reasons the motor could run hot. It's post #4 in this thread: https://www.naxja.org/forum/showthread.php?t=1149596 And the first thing was vacuum leaks. Well, that jogged my memory that I do in fact have two suspicious connections coming off the intake, which I fixed a few days ago - MAJOR improvement!! Not all the way, though - I drove it today with temps in the high 90s and it stayed around 220 most of the time, but sometimes 225 and once 230. I'm also hearing a high-pitched noise that I haven't heard before, so I'm going to keep checking for more vacuum leaks. It seems that this issue, like others I've had before (an occasional rough start, for instance) is caused by several small things adding up, not one specific bad component. But, I certainly don't regret replacing the entire cooling system one part at a time - money well spent!

Boncrshr, man, I feel your pain! If I can offer any advice (not that I'm an expert but I've done a LOT of reading) it would be NOT to do any mods - I've read from a LOT of reputable sources that the stock cooling system is 100% capable of cooling the XJ, even in places like Arizona - but it does have to be maintained and problem-free. I've also read that people can cause overheating issues by swapping out stock parts for "performance" setups - seems to only cause problems. Plus, if you're having any overheating issues, it's a sign that something is out of whack - even if a "performance" part seems to fix it, that's really only a band-aid - seems the very best approach is to get to the bottom of what's actually wrong. Have a look at that list in the link I sent above - the very first item on it made my problem much better!!

Sure appreciate the help, all - I'll update after I do the old cigar-smoke vacuum test and put a gauge on it!

Thetastycat said:

. I've read from a LOT of reputable sources that the stock cooling system is 100% capable of cooling the XJ, even in places like Arizona - but it does have to be maintained and problem-free. I've also read that people can cause overheating issues by swapping out stock parts for "performance" setups - seems to only cause problems. Plus, if you're having any overheating issues, it's a sign that something is out of whack - even if a "performance" part seems to fix it, that's really only a band-aid - seems the very best approach is to get to the bottom of what's actually wrong. Have a look at that list in the link I sent above - the very first item on it made my problem much better!!

Sure appreciate the help, all - I'll update after I do the old cigar-smoke vacuum test and put a gauge on it!

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Very true, the XJ was built on a marginal system that requires everything to be performing perfectly to work. I have lived in Az for 60yrs and can tell you about peoples efforts to cool their motor and all the failed attempts!

boncrshr said:

One of my good friends believes that by lifting my Jeep (4" IRO lift and 33's) I have altered the air flow at highway speeds and that an air dam would help more air flow through the radiator. Thoughts?

Click to expand...

My 2000 has 5.5" of lift and the original radiator, no cooling problems on 100* daily drives, or on trail rides.

Hood vents help with air flow and do reduce underhood temps by 5-8* or more.

You might want to try a ZJ HD 11 blade mechanical fan. It has 11 blades and when you look up the part number (52079654ab) it lists it as "Mechanical. [-HAA], [NMC] Heavy Duty Engine Cooling, [X86+ABD], Calif. Plastic, Fix for TSB 07-06-0, With [NMC]." or a Motorcraft F87A-8600EA (YA220) 11 blade Fan.

Tim_MN said:

My 2000 has 5.5" of lift and the original radiator, no cooling problems on 100* daily drives, or on trail rides.

Hood vents help with air flow and do reduce underhood temps by 5-8* or more.

You might want to try a ZJ HD 11 blade mechanical fan. It has 11 blades and when you look up the part number (52079654ab) it lists it as "Mechanical. [-HAA], [NMC] Heavy Duty Engine Cooling, [X86+ABD], Calif. Plastic, Fix for TSB 07-06-0, With [NMC]." or a Motorcraft F87A-8600EA (YA220) 11 blade Fan.

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This is the first I have heard of this mod.

Has anyone here done this?

RE: vacuum leaks

Its too bad you don't have an ODB-II XJ. Its really easy to spot vacuum leaks by watching the fuel trims with an OBD-II logger. That aside you should be able to stay right at 210F if your cooling system is in good shape, so I suggest that you keep tinkering. Personally, I'm all for aftermarket cooling system parts. Pretty much no part of my cooling system is stock, and with a 180F tstat, my XJ sits at 195-200F no matter what I do. If I manually activate the efan, it stays at 192-196F all the time.

does it overheat idling? if not it could be an airflow issue. if it has ac the condenser could be clogged blocking the air flow. i cant remember if a 95 has a separate sensor for the ecu and dash gauge. if it does a slight grounding issue can cause the gauge to read slightly off.



do you have a way to double check the temperature really is that high?


just rattling off some options.

I have done exactly the same thing replaced the entire cooling system on mine. And replaced the head gasket without machine work was a bad idea. Ended up tearing it down again just dropped my cylinder head off this morning at a machine shop to get it checked out. I even wired my electric fan to run when the ignition is on to try and keep it cool. I’m pretty sure it’s my cylinder head though we will see what they say.

Thetastycat said:

So MAJOR update - I found a fantastic list here of reasons the motor could run hot. It's post #4 in this thread: https://www.naxja.org/forum/showthread.php?t=1149596 And the first thing was vacuum leaks. Well, that jogged my memory that I do in fact have two suspicious connections coming off the intake, which I fixed a few days ago - MAJOR improvement!!

Click to expand...

Very interesting and I will look into it because I have a vacuum leak that has been elusive.

Update:
I replaced the clutch fan with an electric fan last weekend. It was an improvement, but I was still running hotter than I liked on the highway (220 by the gauge). And then on Monday my radiator (CSF 2 row all metal, less than 1 year old) started leaking from the bottom on the driver's side. The plan was to get an aluminum radiator anyways, so I ordered a Chinesium Auto Dynasty from Amazon and spent the 24 bucks for a 4 year replacement warranty. I will buy a Mishimoto someday, but I didn't want to spend the ~500 bucks on a radiator. I ran the Auto Dynasty for almost a year in my previous XJ with no problems. Also, some of the posters in this thread mentioned them.
https://www.naxja.org/forum/showthread.php?t=1150722

So, after 19 miles on the highway this AM, I did not quite get to 210 on the gauge (picrel). I am curious to see what happens this afternoon when I head home.

BTW, I have run CSF radiators before and they have always been durable, but I think I found what killed it. My auxiliary fan had been vibrating more than normal and I didn't think too much of it, but when I pulled it last night I noticed that the plastic feet that sit in the core support had sheared off somehow and there was nothing holding the bottom secure. Considering the leak was right underneath it, I think that was the culprit.

boncrshr said:

Update:
I replaced the clutch fan with an electric fan last weekend. It was an improvement, but I was still running hotter than I liked on the highway (220 by the gauge). And then on Monday my radiator (CSF 2 row all metal, less than 1 year old) started leaking from the bottom on the driver's side. The plan was to get an aluminum radiator anyways, so I ordered a Chinesium Auto Dynasty from Amazon and spent the 24 bucks for a 4 year replacement warranty. I will buy a Mishimoto someday, but I didn't want to spend the ~500 bucks on a radiator. I ran the Auto Dynasty for almost a year in my previous XJ with no problems. Also, some of the posters in this thread mentioned them.
https://www.naxja.org/forum/showthread.php?t=1150722

So, after 19 miles on the highway this AM, I did not quite get to 210 on the gauge (picrel). I am curious to see what happens this afternoon when I head home.

BTW, I have run CSF radiators before and they have always been durable, but I think I found what killed it. My auxiliary fan had been vibrating more than normal and I didn't think too much of it, but when I pulled it last night I noticed that the plastic feet that sit in the core support had sheared off somehow and there was nothing holding the bottom secure. Considering the leak was right underneath it, I think that was the culprit.

Click to expand...

Were you using an aftermarket fan clutch or the MOPAR? I was warned by DPG to use only a MOPAR with the CFS HD radiator. The aftermarkets have those circular fins, that are very near the wider radiators. Other issues and blown motor mounts claimed my first CFS radiator. I installed Brown Dogs and MOPAR. My recent travels, the A/C bracket clutch fan bearing blew out. Fortunately, I caught it in time. So, my 2nd CFS radiator lives another day.

75SV1 said:

Were you using an aftermarket fan clutch or the MOPAR? I was warned by DPG to use only a MOPAR with the CFS HD radiator. The aftermarkets have those circular fins, that are very near the wider radiators. Other issues and blown motor mounts claimed my first CFS radiator. I installed Brown Dogs and MOPAR. My recent travels, the A/C bracket clutch fan bearing blew out. Fortunately, I caught it in time. So, my 2nd CFS radiator lives another day.

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Aftermarket A/C fan and aftermarket fan clutch. I also have Brown Dogs. They are great and give peace of mind.

If only some had said earlier that your not very old radiator had likely gotten blocked because scale had been broken loose from flushing it...