My Never Ending Overheating Problem

[poorboy76]

Hello all,

This is going to be a long post (because I feel like I've covered every possibility). I'm in desperate need of help.

Jeep stats:

• 1991 Jeep Comanche, but for all diagnostic purposes, lets call it a 1998 Jeep Cherokee.
• OBDII swapped from a 1998 Jeep Cherokee
  • Engine, transmission, transfer case, interior, gauges, sensors, doors, overhead console, etc.
  • I've put roughly 70K on this Jeep since owning it, and at least 30K in it's current configuration, minus a few major things.
• Titan Engines 4.0 long block
  • Roughly 1,500 miles on it at this point
  • Balanced rotating assembly
  • Banks Header
  • 99+ Intake
  • 4 hole injectors replaced/installed in the last 30K
  • No sensor related codes present
  • To clarify further, the Jeep has had this configuration, minus the long block, for a long time and a lot of miles
• AW4
  • Filter and fluid changed in the last 30K
  • Stock otherwise
• NP242
  • Not really relevant to this, but might as well list
  • Clocked ~10 degrees to clear NP231 skid plate
• Dana 30, C 8.25, 4.88 gears, rear auto locker, 33-34" tires
  • This has been the same for the last 40+K

I'll do a back story, then list the coolant related issues and attempts.

February of this year, at night, while taking my girlfriend on a date (In Denver, in a pretty good blizzard, and damn cold enough) we get stuck in traffic. Jeep (that I have driven all over the west, in this configuration, for the last 30K) starts to drastically overheat. We're stuck in the middle lane, so I pop it in neutral, and try to get water flowing through the engine. It continues to get hotter. We start moving. Hindsight is always 20/20; I should have pulled over and shut it off. We attempt to keep moving, the temp continues to climb. It maxes out on the gauge. We pull over. The engine is knocking. We are losing power. Pull into a gas station. It's boiling over. Literal melt down. Park it and walk across the street to the bar. Temporary feel good solutions! But I'm confused because I had been driving this thing all week.

At this point, I pull the engine. This engine had been rebuilt, and had an Edelbrock head on it (that I warped like crazy). It had roughly 30K on it. Now it's done for. My only theory for this is the thermostat stuck shut. That's why revving the engine didn't do anything. It was dead heading at the thermostat. I never found anything else that was wrong.

I order a Titan long block because I wanted the least amount of issues, and I want my Jeep to be as reliable as it used to be.

When I installed the engine, I also did:

• New GMB high performance water pump
• New fail safe 210 thermostat
• New hoses
• New radiator
• All new coolant

This was to ensure that I never melted another 4.0

Install the engine, do the break in while running around the city, driving to work...etc. It runs amazing.

Take it wheeling for the first time, and while climbing into the mountains on the highway, I notice it gets hotter than it used to.

I test drive it on I-70 a bunch during the hot summer days (90+ degrees, steep hills going outside of town, torture test as far as I'm concerned).

The max I ever saw in all of my testing was 245, and this happened multiple times. Again, this Jeep has been up these mountains, and much more strenuous ones, fully loaded, a million times.

Explanation of issue:

• It runs cool-ish around town. Sometimes gets above 210, but maintains it, even sitting in traffic with the AC on.
• It gets 220+ while driving on the highway on flat ground. Doesn't really come down, or go up.
• It gets 240+ if you're climbing mountain passes, with the truck empty and the AC off (best case scenario).

Alright, this is the complete list of what I have done since installing the engine in March:

• Thermostats
  • 210 fail safe, 210 regular thermostat, 180 thermostat (current config.)
    • All thermostats had a hole drilled at the "top" to help with air bleeding
  • Replaced the GMB water pump with a completely stock one from Napa
    • Yes, they all spun the correct way
  • Fan clutches
    • 2-3 from parts stores, and now a Mopar one (current config.)
    • Questionable results from these changes, but didn't fix the issue
    • All of these were stock fan clutches
  • Radiators
    • I've replaced the radiator 3 times I believe
      • One was replaced because I theorized that there was junk in the engine from the reman process that had plugged the radiator, but didn't change anything
      • These were all the same Spectre stock radiator off Amazon.
      • Again, I put 70k on this Jeep with a stock radiator, so I don't believe I suddenly need a fancier radiator
  • Coolant bleed
    • I've probably bled the coolant 20 different times this year
    • I had a shop bleed it
    • I used a vacuum bleeder
    • I used the big funnel thing that attaches to the radiator cap interface
    • I've revved it and squeezed the absolute life out of every hose on the Jeep
    • The heater is always turned on and blows hot when the engine is hot
  • Coolant temp sensor
    • I changed it for kicks
    • I verified the temp with an infrared gun
      • When the gauge/OBDII app reads 245, the front of the engine reads from 220-250 on various points across the thermostat housing and head
  • Numerous compression tests before the head gasket
    • Never came back with obvious issues
  • Coolant chemical test
    • Didn't come back with any exhaust in the coolant
  • Head gasket
    • I recently just got it put back together
    • Nothing seemed wrong
    • No obviously blown head gasket
    • The head wasn't warped
    • I discovered that this reman engine is bored .040 over
    • I used a factory thickness MLS gasket for a replacement
    • Used ARP head studs
  • Upper O2 sensor
    • Replaced it in case it was causing the Jeep to run lean
  • Electric fan comes on when it's supposed to, but doesn't stop the overheating under load

Now, it's cooler in Denver. I just got back from the same test drive this evening, with the Mopar fan clutch being the most recent change, and it still got to 225 on the climb. The temperature outside was 60 degrees, for reference.


Needless to say, I am absolutely devastated that I've put this much time and money into this thing that means a lot to me, and it still fails to function. I think I've driven myself stupid with all of the ideas.

So, if anyone reads through this entire boring post, and has an idea that doesn't involve quad electric fans, hood vents, $500 radiators, or anything else that this Jeep has never needed before, I would eternally grateful. Really.

And, thank you in advance.

 

[mewz99]

Kind of off the wall thoughts, but trying to give new ideas. Sorry, I know some of them are obvious.

• Is your engine driven fan shroud installed?
• When you replaced the head gasket, did you punch extra holes in it for what appeared to be coolant passages? (they're not, I'm not suggesting you should have done so)
• How hot is your trans getting? Could that be dumping enough extra heat into the radiator to cause an issue with engine cooling? Maybe lockout clutch is malfunctioning and causing extra heat generation? This would explain why the freeway is so much worse than in town.
• Check your radiator with your temp gun and make sure that it's getting hot when the thermostat housing is hot (which would help verify good flow, at least in theory).
• Could there be enough crap in your coolant that you're clogging ALL your new radiators? If you flush the coolant or even just look in the rad, do you see a bunch of crap floating?
• Try restricting your heater core flow. I had my heater core bypassed (just had the two hoses connected together) and was having pretty severe heat issues - my theory is that most of the coolant flow was going through the bypass instead of the more restrictive radiator.
• Park it at a severe nose-high angle and fill the coolant, then get it hot (with radiator capped) and get nose-high again for an overheat to boiling into the overflow, see if that helps burp any air out. (my buddy had a similar story with his 96 and overheating nose high was what finally fixed it with no real explanation for where the bubble was)
• Use the temp sensor port in the thermostat housing as a bleed for the coolant (maybe this is how you already bled it, if so sorry)
• What's your serpentine belt tension? It should be kinda ridiculous, 160# for a used belt or 180# for a new belt in the 1990 FSM, I think that's consistent with newer models but not sure.

 

[jhenke]

Anything mounted in front of the grill ? Winch, Off road lights, cargo basket ?

 

[Tim_MN]

A late model open cooling system is self-burping. After a couple of warm-up/cool down cycles all air should be expelled.

Does OBD-II live data show rich or lean condition?

Cat converter clogged or broken down matrix?

How many cores in the radiators?

Factory-spec 195* thermostat?

Any leaky frost plugs?

Check into the Ford Explorer or ZJ heavy duty mechanical fan swap.

Motorcraft YA220 11 blade fan.
Hayden 2794 fan clutch.

Dorman 620-112 9 blade fan for the spacer that it comes with to be able to space the motorcraft 11 blade fan back toward the engine, just use the spacer not this fan.

ZJ HD 11 blade 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

 

[lawsoncl]

I'm wondering it the torque converter is locking up as well.

 

[Fred]

Bleed the coolant system? Who does that? It needs to be burped, over and over again. I envy your Comanche, had one for awhile. My 4.1, balanced, ported HO head milled to 11-1(I'm in the Springs), Hesco cam and water pump, bored t-body, Mopar headers, 2.5 inch exhaust on 35's with 4.11's and a stick barely gets warm. Only needs the efan going uphill in 4lo at 11k feet, and multiple stoplights in 90 degree temps. It's a heavy beast with frame reinforcement and a full roll cage. And by the way, I have a late model open cooling system, and it needs burping. I've been doing it for 20+ years on the 90, and the Hesco water pump makes a huge difference.

 

[poorboy76]

Kind of off the wall thoughts, but trying to give new ideas. Sorry, I know some of them are obvious.

• Is your engine driven fan shroud installed?
• When you replaced the head gasket, did you punch extra holes in it for what appeared to be coolant passages? (they're not, I'm not suggesting you should have done so)
• How hot is your trans getting? Could that be dumping enough extra heat into the radiator to cause an issue with engine cooling? Maybe lockout clutch is malfunctioning and causing extra heat generation? This would explain why the freeway is so much worse than in town.
• Check your radiator with your temp gun and make sure that it's getting hot when the thermostat housing is hot (which would help verify good flow, at least in theory).
• Could there be enough crap in your coolant that you're clogging ALL your new radiators? If you flush the coolant or even just look in the rad, do you see a bunch of crap floating?
• Try restricting your heater core flow. I had my heater core bypassed (just had the two hoses connected together) and was having pretty severe heat issues - my theory is that most of the coolant flow was going through the bypass instead of the more restrictive radiator.
• Park it at a severe nose-high angle and fill the coolant, then get it hot (with radiator capped) and get nose-high again for an overheat to boiling into the overflow, see if that helps burp any air out. (my buddy had a similar story with his 96 and overheating nose high was what finally fixed it with no real explanation for where the bubble was)
• Use the temp sensor port in the thermostat housing as a bleed for the coolant (maybe this is how you already bled it, if so sorry)
• What's your serpentine belt tension? It should be kinda ridiculous, 160# for a used belt or 180# for a new belt in the 1990 FSM, I think that's consistent with newer models but not sure.

No need to apologize! I appreciate the questions.

1. Fan shroud is new and intact
2. I did not do this. I've heard of it, but didn't consider that as an option.
3. It's been a while since I checked, but the trans temp seemed appropriate when the engine was damn hot. I'm running an extra cooler in series, so it does still go through the radiator
   1. I did the test where you push the brake while going highway speeds to test the lockup. It worked as it should. However, I might look into this deeper.
4. As far as I can tell, the temperature decreases from driver to passenger, which checks out (I believe). The temperature seems appropriate.
5. After radiator 1 or 2 (can't remember, there have been too many) I flushed the block with a garden hose and a lot of water. I also used an air hose after. All of it dumped into a clean bucket and nothing significant came out.
6. Heater core could make sense. I can pinch it off.
7. This is a good idea. I'm not sure how to make it scorching hot without driving it, as it cools perfectly fine in the driveway. I can get it real hot, then try the severe incline.
   1. It's worth noting that I have been using a steep driveway for all of this as well.
8. I kinda messed with the temp sensor, but feel like I probably introduced more air instead. I haven't perfected that yet.
9. The tension seems appropriate? It doesn't squeal and has almost no deflection.

Thanks again for the ideas!

 

[poorboy76]

A late model open cooling system is self-burping. After a couple of warm-up/cool down cycles all air should be expelled.

Does OBD-II live data show rich or lean condition?

Cat converter clogged or broken down matrix?

How many cores in the radiators?

Factory-spec 195* thermostat?

Any leaky frost plugs?

Check into the Ford Explorer or ZJ heavy duty mechanical fan swap.

Motorcraft YA220 11 blade fan.
Hayden 2794 fan clutch.

Dorman 620-112 9 blade fan for the spacer that it comes with to be able to space the motorcraft 11 blade fan back toward the engine, just use the spacer not this fan.

ZJ HD 11 blade 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

That has always been the case for me, and I've done this a lot on these open cooling systems.

It doesn't trigger a code, but I can map fuel trims. I'm not really sure what's normal for those numbers, but I have observed them.

The cat is only a few years old, and was replaced after all of my engine issues of the past, so I don't believe it to be clogged.

It's a stock style radiator, so whatever that is. I can't recall, but I'd guess two?

I've had a few. I tried the 195, which made it run hotter than the previous engine that also had a 195. Now I'm running a 180, and it will still run near 210 on the highway. On previous XJ's with 180 thermostats, they have always run below 210, no matter the conditions.

No frost plug issues that I know of. At least they aren't leaking coolant out.

The upgrades are options, but that doesn't answer the question of why it suddenly runs hot, when it never did before the new long block.

Regardless, thanks for the coolant upgrade info!

 

[poorboy76]

Anything mounted in front of the grill ? Winch, Off road lights, cargo basket ?

Good question. I have always had a winch that obstructed the air flow a bit. However, it's probably been on the front of the Jeep for 50-60k miles.

In the name of testing, I removed it earlier this year. It changed absolutely nothing. I also put spacers on the hood hinges, which also did nothing.

 

[poorboy76]

I'm wondering it the torque converter is locking up as well.

I did the highway test where you tap the brake while going highway speeds, and it seems to function properly. However, I think I should do some more testing with this.

 

[poorboy76]

Bleed the coolant system? Who does that? It needs to be burped, over and over again. I envy your Comanche, had one for awhile. My 4.1, balanced, ported HO head milled to 11-1(I'm in the Springs), Hesco cam and water pump, bored t-body, Mopar headers, 2.5 inch exhaust on 35's with 4.11's and a stick barely gets warm. Only needs the efan going uphill in 4lo at 11k feet, and multiple stoplights in 90 degree temps. It's a heavy beast with frame reinforcement and a full roll cage. And by the way, I have a late model open cooling system, and it needs burping. I've been doing it for 20+ years on the 90, and the Hesco water pump makes a huge difference.

Bleed, burp, choke, strangle, scream at...I've done it all!

I appreciate it. It used to be worthy of envy, now it just wants to die.

I've never had a problem like this with any of the numerous 4.0's I've owned over the years. Like I said, I'm at a complete loss.

That's a nice looking 2 door! Definitely looks on the heavy side.

 

[Fred]

As I said, Hesco water pump. They are frequently sold out. What's another $200+ difference make. LOL.

 

[Rayos-x]

Mine was prone to overheat for the first year or so. I tried a 180 degree thermostat, fan clutch, a 2 or 3 row aluminum radiator, nothing helped. It would tickle overheating but not quite go there until a cannonball run from LA to Phoenix at about 80mph, with the A/C on in 110 degrees. It all of the sudden pegged the gauge, started beeping and boiling over. It took forever to cool down after that heat soak. Nothing helped until I put back an OEM style radiator from NAPA and replaced the coolant with 50/50. In my case, it seems I had too much antifreeze and not enough water. It's getting warm again now, but I noticed part of the shroud has gone missing. My old landlord in LA and his buddies had about 5 XJs they took rock crawling in Parker every few weeks. He said the 4.0s always run a little warmer than you might like, and that every component needs to be just right to keep them cool enough.

 

[maxbraketorque]

Definitely an off-normal issue, so need to look for true issues rather than consider better parts. I like the idea of checking to see if the cat is clogged. I also wonder how full your overflow bottle is getting when the engine gets toasty. The question there is whether the HG is leaking. If its leaking, then I'd expect the overflow bottle to become very full after a drive. I'd also consider the possibility that the radiator is clogged.

 

[CHEROKEE-RENIX-88]

Kind of off the wall thoughts, but trying to give new ideas. Sorry, I know some of them are obvious.

• Is your engine driven fan shroud installed?
• When you replaced the head gasket, did you punch extra holes in it for what appeared to be coolant passages? (they're not, I'm not suggesting you should have done so)
• How hot is your trans getting? Could that be dumping enough extra heat into the radiator to cause an issue with engine cooling? Maybe lockout clutch is malfunctioning and causing extra heat generation? This would explain why the freeway is so much worse than in town.
• Check your radiator with your temp gun and make sure that it's getting hot when the thermostat housing is hot (which would help verify good flow, at least in theory).
• Could there be enough crap in your coolant that you're clogging ALL your new radiators? If you flush the coolant or even just look in the rad, do you see a bunch of crap floating?
• Try restricting your heater core flow. I had my heater core bypassed (just had the two hoses connected together) and was having pretty severe heat issues - my theory is that most of the coolant flow was going through the bypass instead of the more restrictive radiator.
• Park it at a severe nose-high angle and fill the coolant, then get it hot (with radiator capped) and get nose-high again for an overheat to boiling into the overflow, see if that helps burp any air out. (my buddy had a similar story with his 96 and overheating nose high was what finally fixed it with no real explanation for where the bubble was)
• Use the temp sensor port in the thermostat housing as a bleed for the coolant (maybe this is how you already bled it, if so sorry)
• What's your serpentine belt tension? It should be kinda ridiculous, 160# for a used belt or 180# for a new belt in the 1990 FSM, I think that's consistent with newer models but not sure.

I agree with this, My 88 would yard drive and cruise fine without the shroud but any type of "spirited" driving or stop and go it would get hot. But my bet is like you said the Head Gasket wholes. Also have you thought about an open cooling system if you cant get it too stop getting hot?

 

[poorboy76]

Mine was prone to overheat for the first year or so. I tried a 180 degree thermostat, fan clutch, a 2 or 3 row aluminum radiator, nothing helped. It would tickle overheating but not quite go there until a cannonball run from LA to Phoenix at about 80mph, with the A/C on in 110 degrees. It all of the sudden pegged the gauge, started beeping and boiling over. It took forever to cool down after that heat soak. Nothing helped until I put back an OEM style radiator from NAPA and replaced the coolant with 50/50. In my case, it seems I had too much antifreeze and not enough water. It's getting warm again now, but I noticed part of the shroud has gone missing. My old landlord in LA and his buddies had about 5 XJs they took rock crawling in Parker every few weeks. He said the 4.0s always run a little warmer than you might like, and that every component needs to be just right to keep them cool enough.

Interesting point. I have religiously used full strength coolant that I dilute down with bottled distilled water at home. I'd say it was close enough to 50/50 to not make a difference, but who knows at this point. I suppose I could try putting more water in, although that's a risky game in the Colorado winters.

 

[poorboy76]

Definitely an off-normal issue, so need to look for true issues rather than consider better parts. I like the idea of checking to see if the cat is clogged. I also wonder how full your overflow bottle is getting when the engine gets toasty. The question there is whether the HG is leaking. If its leaking, then I'd expect the overflow bottle to become very full after a drive. I'd also consider the possibility that the radiator is clogged.

That's exactly where I'm at. I've put 50k+ on this Jeep in the current configuration, doing the exact things I'm trying to do now. It doesn't magically need upgrades.

I drove it all last week. We had a big snow storm here, so it never got above 45 degrees outside. The Jeep did really well, and ran exactly where I would expect it to with a 180 thermostat. Yesterday however, it was a little warmer outside, and it did get near the 210 mark on the drive home from work.

I took the IR gun and measured some temperatures.

The transmission pan was roughly 170 degrees.

The exhaust was a little more inconsistent to measure with the IR, so I don't totally trust the numbers.

Pre-cat pipe temperature was roughly the same as the post-cat pipe, at around 420 degrees. Again, these numbers were a little "cloudy" to get.

However, I'd assume that pre-cat temps would be higher than post-cat temps if the cat was plugged?

As far as the HG, it had the same issues before and after I changed the head gasket. I used a nice MLS gasket with ARP studs, so I'd hope it isn't leaking.

However, I'll keep an eye on the overflow. That's a good idea.

At this point, there's no way the radiator is clogged. I've literally put four radiators in it in the last 9 months, with no change in behavior. And I flushed the block after radiator #2 or 3.

Thanks for the ideas! I'll report back once I do some more testing.

 

[poorboy76]

I agree with this, My 88 would yard drive and cruise fine without the shroud but any type of "spirited" driving or stop and go it would get hot. But my bet is like you said the Head Gasket wholes. Also have you thought about an open cooling system if you cant get it too stop getting hot?

I still have the old head gasket, so I can compare it to the one that I installed. I've never had to do that on an engine, so I'd be curious as to why that would be necessary now.

I have an open cooling system, as this is essentially a 1998 XJ, mechanically and electrically.

 

[CHEROKEE-RENIX-88]

I still have the old head gasket, so I can compare it to the one that I installed. I've never had to do that on an engine, so I'd be curious as to why that would be necessary now.

I have an open cooling system, as this is essentially a 1998 XJ, mechanically and electrically.

Seeing as you said you have an all new cooling system basically, I was reading what others have said do you think its possible that your coolant is going through the bypass and not going thought the rad? You mention you still have ac, when you had the rad out did you do anything to clean the condenser. I know its unrelated to jeeps but when I had my Chevy blazer I had a bunch of leaves, twigs and bugs clogged up on my condenser and a lot of fins bent and it would get hot. cleaned and straitened that and she ran a cool 180. One last thing, have you tried to "Gut" a thermostat? Don't run no thermostat as it can cause the coolant to run too fast through the rad and doesn't have enough time to actually cool the coolant.

 

[maxbraketorque]

Post-cat exhaust gas temperature is supposed to be significantly hotter, by at least 100F or something like that. You may not see 100F because you are measuring the temperature of the tubing, but post-cat temperature should be consistently and obviously higher. When I measured my XJ some months ago, I saw clearly higher post-cat.