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Diagnosing a slight overheating issue

6K views 88 replies 22 participants last post by  colorubi 
#1 ·
Okay so I've commented on a few other users threads asing questions but I think its time to start one for myself to keep my thoughts in one place.

Big thanks to TangoFox and Jerry B for the help they've provided me in the misc threads.

The Jeep: 2000, 4.0L Auto with 93k on it. Stock everything.

I'm chasing down a slight over heating issue. Quick recap, I had the 32RH transmission rebuilt in february due to user error and swamping it. Heres a few scenarios since I've gotten it back.
1) Got it back, took it on the beach in 90+ degree weather, had it in 4H due to sugar sand and it in 1st gear only, noticed it started to heat up past 210 on the beach. Once I got on the pavement it went back down.

2) Fast forward and I'm sitting in a fast food line in 90+ degree heat with AC at full blast and it creeps up past 210, get on the pavement and it goes back down.

3) Driving it on the highway upwards of 65+ MPH it goes a needle length above 210, lower my speeds to below 65mph and it goes back down.

4) Idle a few minutes with AC off and the temp goes up but comes back down once moving.

Now, could this have ANYTHING to do with the transmission being rebuilt or is it simply coincidence? How about the fact that temps in FL have been over 90 lately?

Things Ive checked:
1) Fan/Fan clutch - all signs point to the fan clutch being in working order. Stops immediately when the motor has been running for awhile and I turn it off. Hard to spin when the motor is hot, "easy" to spin when the motor is cold.

2) Lower radiator hose. The coil is in the hose. I popped open the radiator cap and tried to squeeze the hose, the hose is firm.

3) Oil color on dipstick and and under the cap - both look like used oil colors to me, I see no indications of a milky substance or anything to indicate that the head is cracked and therefore allowing coolant in.

Things I need to check/replace in this order based on easiest and cheapest:
1) Fluids (its below the "full line")
2) Radiator cap (18lbs)
3) Water pump
4) Heater core

Anyone have a similar situation and can think of what they need to check? My biggest fear is a cracked head but my buddy whos pretty handy with vehicles says that if the had was cracked he doesnt think it would ever stop "over heating". Now I bought the Jeep in December and havent paid much attention to the coolant level as I've never had an issue with over heating but I did notice yesterday its below full. Is it normal for a vehicle to lose some coolant over time or do I have the dreaded cracked 0331 head casting as I clearly am missing coolant. I dont know the last time any was added or topped off so I will be doing so.

Any advise anyone has will be greatly appreciated. I want to get this sorted out so I can justify ordering a lift kit and wheels/tires.
 
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#2 ·
I would lean towards replacing the fan clutch first since it's original and cheap to do. Do a radiator flush, burp, and making sure the fins are clean of debri, caked on dirt, etc.. and not bent fins. The clutch and/or radiator(if both original) are the likely culprits of your overheating issues. As for the fan clutch, it it freely spins 5 rotations or more when cold tested, it needs to be replaced.
 
#4 ·
I would lean towards replacing the fan clutch first since it's original and cheap to do. Do a radiator flush, burp, and making sure the fins are clean of debri, caked on dirt, etc.. and not bent fins. The clutch and/or radiator(if both original) are the likely culprits of your overheating issues.
So the bottom of the radiator definitely has debris on it and I think some of the fins may be slightly damaged. I really dont think its the fan clutch though just because all signs point to it functioning correctly. I guess it doesnt hurt replacing. I'd rather not replace the radiator first as thats the most expensive part.

Does any of this sound like a cracked head? Also, I'm pretty sure I have a bad valve cover gasket...
 
#5 ·
When driving on the beach it went probably 2-3 needle lengths, when idling with AC 2-3 needle lengths, so half way in between 210 and the line before redline. When driving 65+ just one needle length.

I think I've seen you driving around St. Augustine a few times hah
 
#8 ·
Prior to changing out my radiator a year or so ago mine acted the SAME way & the only reason I changed it was because it started leaking.

Yea, I imagine you have. I fish the beach pretty regularly.
What radiator did you go with? I was shopping around mushimoto and was waiting for my buddy to get in touch with me regarding a company he said makes radiators here in the USA.
I highly doubt a cracked head. Do as I suggested, especially flushing/burping/hosing off debri/straighten the fins of the radiator. The radiator and clutch are wear items and unfortunately will fail. You have to think 14yrs of use out of them is a pretty good track record and more than likely will need to eventually need replacing. It's good to get in a habit of checking your fluids regularly(oil/coolant/steering) since you stated you haven't even looked at the coolant level since owning the Jeep the past 7 mos. It's normal for some coolant/oil burn off so just make it a point at least every few wks to check your fluids and not go by warning gauges to tell you if there's an issue because by then it may be too late.
A friend said to top the coolant off with water and keep an eye on it as well so I guess I'll go that route right now, clean up the radiator, and start pricing out new equiptment. You're right about 14 years being a good run on them. I've had the jeep since December and changed the oil out immediately, we just rolled 5k over on the oil last weekend and its getting ready to be changed out again. I run full synthetic in all my vehicles and change them at 5k so the jeep doesnt see much road time as its a weekend vehicle. So far the jeep has not gotten close to red line on the gauges so I havent really "over heated" it per say.
 
#7 ·
I highly doubt a cracked head. Do as I suggested, especially flushing/burping/hosing off debri/straighten the fins of the radiator. The radiator and clutch are wear items and unfortunately will fail. You have to think 14yrs of use out of them is a pretty good track record and more than likely will need to eventually need replacing. It's good to get in a habit of checking your fluids regularly(oil/coolant/steering) since you stated you haven't even looked at the coolant level since owning the Jeep the past 7 mos. It's normal for some coolant/oil burn off so just make it a point at least every few wks to check your fluids and not go by warning gauges to tell you if there's an issue because by then it may be too late.
 
#14 ·
Thats weird that you've replaced pretty much the entire cooling system and it didnt fix it ...

Whats the possibility that my new transmission running thru the system is just too much for the radiator to handle?? What about putting in a auto trans cooler completely bypassing the radiator?
 
#16 ·
Doubt the transmission would overheat the engine, otherwise you woukd be having tranny issues, automatics do not like heat.

Have you tested the coolant system pressure with the engine running?
I have not, would you mind explaining how to do so?

Pop the raditor cap open, turn on the jeep and let it run to see if coolant is flowing? just a guess there really, dont know if thats the process
 
#20 ·
Okay so Friday I topped off my coolant, it was a couple inches below the full line. I don't believe I have a cracked head as the oil looks perfectly normal on the dipstick and under the cap. So I drove it all Friday with no issues, now this was at night and in the rain so maybe it played an effect.

Today on the way to work I drove at 70mph and had no over heating issues until I slowed down to 20mph due to traffic. Needle went up about one needle length over 210 and then back down after cruising a bit. I had the AC on at this time. Then I left work (raining a little) and drove with the AC on setting 3 of 4 and in stop and go traffic. No issues at all, needle sat half on the 210 line and half over. Got home and parked the jeep half way in the garage (engine in exhaust out) and left it sitting for about 6 minutes with the AC on full blast. This was the result. Seems like the needle held right here and didn't move. I ended up turning the jeep off. All my hoses look fine, no play in the fan at all. This weekend is thermostat, flush and burp and will go from there.
 

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#21 ·
Make sure you drill a bleed hole in the thermostat.
But seeing this and from what you are saying, I would say fan clutch. I had the same issues back in Oct. Replaced the fan clutch first time in 14 years and it fixed my issue until the water pump decided to fail after 4 years and 35k miles. But if you never changed your fan clutch yet, I would change that.
 
#22 ·
Thermostat kind of baffles me .. few people think thats what the issue is but I dont really know. I guess it could be in the process of going bad and hanging up... figure its a cheap part might as well replace it.

The more I think about the fan clutch the more I think I may just do it. I have done every test mentioned, and all the tests point to it working fine but again, its another cheap part and the walk throughs dont seem too hard to do.
 
#23 ·
A needle width above 210 is not overheating. There is going to be some change in the system.

Driving in the sand in 4H puts extra load on the tranny. The fluid is cooled by the radiator, extra work means you're pumping more heat into the system.
 
#27 ·
A needle width above 210 is not overheating. There is going to be some change in the system.

Driving in the sand in 4H puts extra load on the tranny. The fluid is cooled by the radiator, extra work means you're pumping more heat into the system.
Originally in the sand I chalked it up to being 90+ degrees out, and running first gear thru pretty soft sugar sand, however the issue continued
I don't see that there is an "issue." Except maybe with overly optimistic expectations.
See my concern was I drove the jeep from December to March and never had this issue. It didnt start to pop up until I had the transmission rebuilt and of course our summer hitting.
That looks normal to me (especially in 90+ degree weather), however the scale on the TJ gauges suck.
I would like to know the actual temp when "one needle length over 210"
That picture was taken inside my garage. When I was driving and it happened it was about 7:45 in the morning, mid 70 degree's out, wasnt quite 90 yet.
-Low Coolant can lead to slight overheat
-Could need a new radiator cap
-Check belts and water pump
-Check radiator for excessive bent fins and blockage
-Radiator have built in trans cooler? Check trans fluid level.
-Check for exhaust leak, this can lead to overheating
-Check fan relay and wiring
-Low Coolant can lead to slight overheat - Topped off coolant friday night, thought it solved the problem and it may have if this is normal behavior its exhibiting.
-Could need a new radiator cap - Picking Up
-Check belts and water pump - Will check for sure after cap, fan clutch, and thermostat
-Check radiator for excessive bent fins and blockage - there are some bent fins on the radiator on the inside. There were slight debris build up towards to bottom of the front but I cleaned that up.
-Radiator have built in trans cooler? Check trans fluid level. - Trans fluid is fine, level is good and color clear red
-Check for exhaust leak, this can lead to overheating - Havent heard, smelled, nor had any dummy lights pop up indicating an exhaust leak but I havent done any type of smoke check
-Check fan relay and wiring - not quite sure how to do this so I'll have to look into it. I know the fan spins great though?
 
#26 ·
-Low Coolant can lead to slight overheat
-Could need a new radiator cap
-Check belts and water pump
-Check radiator for excessive bent fins and blockage
-Radiator have built in trans cooler? Check trans fluid level.
-Check for exhaust leak, this can lead to overheating
-Check fan relay and wiring
 
#29 ·
You might consider getting a more accurate read of the temp:
(I ordered the cheaper way, but it'll take a few weeks for the item to get to me (ships from China))

For the coolant level, at 210° the overflow bottle should be between Add and Full

If you get the Temp to 210° and slightly below at highway speeds, but increases Temp at low speeds and at idle (with the A/C off), I would suspect the fan clutch.

FWIW, when I'm at 70+mph, I'm slightly above 210° (like in your pic).
At 55 and below (incl idle), with a/c off, I'm at slightly below to exactly at 210°

As long as your Temp doesn't rise above what you show in the pic, you should be ok.

BTW, I recently had a problem with my lower radiator hose collapsing at highway speeds (hose didn't have a spring in it. Seems many new hoses don't). Replaced with an OEM with a spring, and my problem was solved.
 
#30 ·
You might consider getting a more accurate read of the temp:
(I ordered the cheaper way, but it'll take a few weeks for the item to get to me (ships from China))

For the coolant level, at 210° the overflow bottle should be between Add and Full

If you get the Temp to 210° and slightly below at highway speeds, but increases Temp at low speeds and at idle (with the A/C off), I would suspect the fan clutch.

FWIW, when I'm at 70+mph, I'm slightly above 210° (like in your pic).
At 55 and below (incl idle), with a/c off, I'm at slightly below to exactly at 210°

As long as your Temp doesn't rise above what you show in the pic, you should be ok.

BTW, I recently had a problem with my lower radiator hose collapsing at highway speeds (hose didn't have a spring in it. Seems many new hoses don't). Replaced with an OEM with a spring, and my problem was solved.
Hey Tony, thanks for the input. I actually followed your thread (and commented on it I believe), checked my lower radiator hose because of it and unfortunately it has a spring and no play to it. I say unfortunately because I would have loved for that to have been my trouble hah
 
#32 ·
How high have you seen the Temp? (Does it get past the "0" in 210)
Yes, and before I topped off the coolant it went 2, maybe 3 needle lengths past the 210 marker. I would call it halfway between 210 and the next white line. Its never gone above that though, and that was only once. I was sitting in a chick fila drive thru line in 95+ degree weather for like 10 minutes...
 
#33 ·
Okay due to some unforeseen family issues I never had a chance to take a whack at this however I went and picked up a new thermostat and fan clutch. Hopefully can find some time to change these.

So it's 90 degrees here in Florida right now, drove with the AC on full blast getting gas and whatnot, never goin above 30mph, and the needle never went above 210. Now sitting at idle for 6 minutes it moved up to where it is in photo one, then after 16 minutes to where it is in picture 2. This is NOT normal... Correct?
 

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#43 ·
So it's 90 degrees here in Florida right now, drove with the AC on full blast getting gas and whatnot, never goin above 30mph, and the needle never went above 210. Now sitting at idle for 6 minutes it moved up to where it is in photo one, then after 16 minutes to where it is in picture 2. This is NOT normal... Correct?
Thermostat is probably ok as you're at 210° when doing 30mph.
A new fan clutch may help.

Does it stay at 210° at idle if you have the A/C off?
 
#39 · (Edited)
Mine does this with AC on full blast in Texas summer heat. Sat at a train crossing for 23 minutes with outside temp @ 97*. Needle never went more than between 1 and 0 on 210. I was assured by many that was ok. I have done almost as much as you. Radiator, caps, thermostats, and a water pump. All I have left to change out is fan clutch and hoses and my entire cooling system will be replaced. Going to follow you along on this one.
 

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#46 ·
Alright, one cracked thermostat housing later and the thermostat is changed. So I ran th jeep by advanced auto and we watched the temp climb to 217 in a few minutes while in the shade. My buddy who works there figured a bad thermostat too. So once we pulled the thermostat out we put it in some boiling water and sure enough it would barely open. Put the new one in the water and it opened right up. So we started it up, it went above 210, we put coolant back in it and it started to move down. Didn't have time to do the fan clutch but as of right now the jeep is sitting right at 210 with part of the needle to the left of it for about 10 minutes with the AC running full blast.
 

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#47 ·
Okay so after changing the thermostat and sitting with the AC going full blast in 91 degree weather it started to heat up. Sat pretty steady here but this still concerns me. My buddy told me in this heat it's normal. Can anyone confirm that on their stock radiator TJ they can sit in 90+ degree heat with the AC going full blast and not have the temp gauge move at all..? Guess I'm just trying to figure out if this is normal
 

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#48 ·
Can anyone confirm that on their stock radiator TJ they can sit in 90+ degree heat with the AC going full blast and not have the temp gauge move at all..?
Looks like you're at about 225+° there.
Does the idle pick-up? (the on board computer will kick-up the idle when in an overheat condition).

You said that it creeps up with the A/C off, correct?
Did you install the fan clutch?
Did you flush the Radiator?
Do you get to the left of 210° when you get moving again?
I know it's hot at 90°, but turn on the heater, full blast, to see if the temp drops. You should only need to do it for 5 min.

Is this a temporary condition, i.e., you get back to 210° when you start moving?
 
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