Overheating problem

Dvaniwaarden11

Dvaniwaarden11

TJ Enthusiast
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Supporting Member
Joined
Feb 28, 2024
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148
Location
Southern California
Hows it going fellas. I've got an overheating problem with my 1997 TJ 4.0 5 speed. 4.88 gearing on 35s.

My Tj has a brand new motor in it with probably only 2-3k miles on it. When my shop put the new 4.0 in, they replaced every part of the cooling system. Radiator, pump, thermostat, hoses etc are all new.

Since its started to heat up in california and we're into the 90s now, I've been taking my jeep on some longer drives. I've also been using the air conditioning. After about 45 minutes of highway driving (65-75 mph) my gauge reads at 230, and then eventually moves into the bottom part of the red on the gauge. (I don't think the gauge is the issue because the cold AC air would turn into lukewarm air and the floorpan would be noticeably warmer)
When this happened a couple days ago I would lift off the gas and coast in gear until I was at 45-50 mph in the slow lane to let the engine cool using air flow and not putting any load on the engine. It would eventually move back down to 210 and I limped it the rest of the way home. I don't have any issues driving on the side streets of any overheating and I have zero leaks anywhere. My fan clutch has resistance, I have plenty of fluid and nothing using coolant, and the entire cooling system is new. I have a winch on the front of my jeep but I doubt that is an issue in airflow because that doesn't make sense to me. I'm at a loss for what the issue could be. Is running my AC at a higher speed causing too much load on the engine? Any ideas for a direction I can start looking in?

On a cooler day if I would ever be driving up a long hill my engine would get hot and I would just limp the way to the top of the hill but I felt that had more to do with my 4.88 gearing and figured that its a jeep and I should expect to do 65 going up a long hill, but maybe I'm wrong and my jeep should be able to do that no problem?

Would just love some advice.
Thanks,
Dylan
 
Agree with Mac. What brand cooling system components were installed? With a brand new OEM radiator and water pump I can drive over the Grapevine in 105 degree heat and never see engine temps above 210.

The mechanic may have installed cheap cooling system components that are ineffective.
 
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Looks like you've blocked most of the airflow through the grill.
 
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I’m not sure what brand my thermostat is but judging by my radiator being a cheap radiator I assume my thermostat is cheap too. The issue is, these parts are all brand new. All within the last 3 years with only 2,000 miles on them and the motor. Even if they’re cheap parts they shouldn’t be failing already.

I know my winch will block some of the airflow but tons of people have winches with no issues.

Not sure what to target. My first instinct is to replace the thermostat since that will be the cheapest and fastest to replace.

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Denso radiators are just fine. It would be what I would buy if I needed one.

I have a Napa Spectra. By all accounts it should be junk...but it works.

I'd get a laser IR thermometer and start narrowing down where your issue is. Closer the better...those are really only accurate to a couple of inches.

I'd measure the water neck before and after the thermostat. Both hoses. Both sides/tanks of the radiator and probably top and bottom. Water pump.

Let's do some figuring before firing off the parts cannon.

Doing a good Thermocure flush also wouldn't hurt. Lots of junk can get into engines when they're rebuilt.

-Mac
 
macleanflood said:
Denso radiators are just fine. It would be what I would buy if I needed one.

I have a Napa Spectra. By all accounts it should be junk...but it works.

I'd get a laser IR thermometer and start narrowing down where your issue is. Closer the better...those are really only accurate to a couple of inches.

I'd measure the water neck before and after the thermostat. Both hoses. Both sides/tanks of the radiator and probably top and bottom. Water pump.

Let's do some figuring before firing off the parts cannon.

Doing a good Thermocure flush also wouldn't hurt. Lots of junk can get into engines when they're rebuilt.

-Mac
Click to expand...

I’ve never done a thermocure flush or heard of one before. Are there instructions on it somewhere here on the forum?

I’ll order an IR thermometer since I don’t have the tool already and get it nice and hot and then check everywhere. I should be looking for a higher variable in heat than anywhere else correct? Naturally my top hose should be hotter than the lower hose anyways but besides that I’m not sure what a normal temperature for certain parts of the cooling system should be.
 
macleanflood said:
Well we know the thermostat should keep the system at 210 degrees. So start there...

-Mac
Click to expand...

So I ran my Jeep today to get it warm in the parking lot for 10 minutes. Then while I was parked I sat in the Jeep with the hood off and gave it some acceleration in neutral for about 10 minutes. Below we’re my readings with the AC on full blast:

Gauge 215-220

Upper hose 215

Lower hose 200

Upper radiator 150

Lower radiator 135

Thermostat housing 240

Water pump 235

Radiator cap 180

Reservoir 155

What’s frustrating is it won’t overheat while I’m sitting in the parking lot idling and running it in neutral at 3k RPMs. It overheats on the freeway but by the time I pull off to the side of the road the temperature is already falling back into normal limits (210-220)

I wish I was gushing fluid somewhere so I would at least know what to fix. My first instinct is to swap the thermostat because it’s cheap and the easiest to do. Problem is that I’m not able to replicate the overheating in a parking lot. So my clutch fan should be fine. My thermostat is clearly working since I notice a change in temperature on both hoses and the radiator is different temperatures from the top to bottom. Which also tells me my pump is operating as it should be.
I am seriously at a loss for this. I’m tagging one of the members in this thread who I’ve seen help out a bunch of people with their overheating problems to maybe get some more eyes on this thread.
@mrblaine
 
My thoughts:

On the hwy, the engine is working harder to push a brick through the air at speed than revving it in the parking lot. The hood being off will help with cooling.

On the hwy, the fan is not needed, the cooling is from the high pressure air being forced through the rad. Most vehicles with electric fans shut them off above 45 to 50 MPH in fact.

The faster you go, the more your winch and bumper are causing a low pressure area right in front of the rad as the air is diverted around to the left, right, and above.

It's possible that the aftermarket rad is not cooling as much as an OEM would as well.

I just drove my stock Rubicon 350 mi or so from Nashville TN to Warner Robins GA in 100 deg heat at 70 to 75 MPH with the AC blasting. The temps on an OBDII scanner ranged from 200 to 225 deg depending on whether I was going uphill or downhill. Highest temps were going up Monteagle Mtn and lowest going down the other side. It does have a MOPAR radiator, no winch, stock size tires, MT.
 
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JKP said:
My thoughts:

On the hwy, the engine is working harder to push a brick through the air at speed than revving it in the parking lot. The hood being off will help with cooling.

On the hwy, the fan is not needed, the cooling is from the high pressure air being forced through the rad. Most vehicles with electric fans shut them off above 45 to 50 MPH in fact.

The faster you go, the more your winch and bumper are causing a low pressure area right in front of the rad as the air is diverted around to the left, right, and above.

It's possible that the aftermarket rad is not cooling as much as an OEM would as well.

I just drove my stock Rubicon 350 mi or so from Nashville TN to Warner Robins GA in 100 deg heat at 70 to 75 MPH with the AC blasting. The temps on an OBDII scanner ranged from 200 to 225 deg depending on whether I was going uphill or downhill. Highest temps were going up Monteagle Mtn and lowest going down the other side. It does have a MOPAR radiator, no winch, stock size tires, MT.
Click to expand...

If airflow is truly my problem, I’m not sure if adding louvers would help very much and it also doesn’t make sense that a ton of jeeps have winches but most of those jeeps are completely fine and don’t overheat. Sure I could spend 1k on a mopar radiator, but my aftermarket radiator should be working completely fine right now. Or rather fine enough with only 2,000 miles on it. I guess if everything is operating as it should and I still have overheating problems, it might be time to shell out a bunch of money for a mopar radiator. However I’d love wait for that to be a last resort. I wonder if an auxiliary fan would help increase airflow?
 
Dvaniwaarden11 said:
So I ran my Jeep today to get it warm in the parking lot for 10 minutes. Then while I was parked I sat in the Jeep with the hood off and gave it some acceleration in neutral for about 10 minutes. Below we’re my readings with the AC on full blast:

Gauge 215-220

Upper hose 215

Lower hose 200

Upper radiator 150

Lower radiator 135

Thermostat housing 240

Water pump 235

Radiator cap 180

Reservoir 155

What’s frustrating is it won’t overheat while I’m sitting in the parking lot idling and running it in neutral at 3k RPMs. It overheats on the freeway but by the time I pull off to the side of the road the temperature is already falling back into normal limits (210-220)

I wish I was gushing fluid somewhere so I would at least know what to fix. My first instinct is to swap the thermostat because it’s cheap and the easiest to do. Problem is that I’m not able to replicate the overheating in a parking lot. So my clutch fan should be fine. My thermostat is clearly working since I notice a change in temperature on both hoses and the radiator is different temperatures from the top to bottom. Which also tells me my pump is operating as it should be.
I am seriously at a loss for this. I’m tagging one of the members in this thread who I’ve seen help out a bunch of people with their overheating problems to maybe get some more eyes on this thread.
@mrblaine
Click to expand...

If you brought it to me with those symptoms, I'd say the radiator was junk.
 
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I'm wondering if you're getting enough coolant flow from your water pump.

If the bottom of the radiator is 135 and the lower hose is 200...that makes me think pump failure.

If seen the impeller blades completely disintegrate on some water pumps.

Pressure test perhaps?

Although if @mrblaine says radiator then a Denso is around a $100 fix...

-Mac
 
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An auxiliary fan in front of the condenser is only going to reduce air flow. Try sealing up any gaps between the radiator and the core support, Pool noodles or Plumbing pipe insulation is cheep and will work. Put the hood back on and work from there.
 
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5TTTj said:
An auxiliary fan in front of the condenser is only going to reduce air flow. Try sealing up any gaps between the radiator and the core support, Pool noodles or Plumbing pipe insulation is cheep and will work. Put the hood back on and work from
Click to expand...
Unfamiliar with the term core support. Are you talking about insulating below the radiator?
 
mrblaine said:
If you brought it to me with those symptoms, I'd say the radiator was junk.
Click to expand...
Sounds like I’m replacing my radiator.

I know you’re big on mopar radiators. Are there any others that you’d recommend? Very few mopars around anymore and the one I found on eBay was $900…
 
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Dvaniwaarden11 said:
Sounds like I’m replacing my radiator.

I know you’re big on mopar radiators. Are there any others that you’d recommend? Very few mopars around anymore and the one I found on eBay was $900…
Click to expand...

Dvaniwaarden11 said:
Sounds like I’m replacing my radiator.

I know you’re big on mopar radiators. Are there any others that you’d recommend? Very few mopars around anymore and the one I found on eBay was $900…
Click to expand...

I was in the same situation as you although it didn't get that hot but it did reach 230. I was putting off changing the radiator and cooling components until my radiator blew up. So the Mopar cost about 480 and I opted for one for a little more than 100 dollars from Amazon I changed the thermostat for a 195 degree stant I changed the lower and upper hose since I was working there I did a flush with thermocure and now I almost always run below 210 even with air conditioning. I don't know if this radiator will last long but it was impossible for me to afford the Mopar at that time.
 
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