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Improving the cooling on our TJs

mrblaine

Crew Member
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Nov 20, 2015
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Quail Valley, CA
My water pump on my '05 went out, and the radiatorblew it's top as a result. I have since replaced the water pump with one from FlowKooler, the fan clutch with Hayden 2771, the radiator with an aftermarket aluminum model from ExtremeTerrain, as well as the thermostat and hoses. I ran a chemical flush, then flushed with water before replacing with Zerex coolant for Mopar vehicles.
Now the engine overheats constantly, regardless of ambient temperature or traffic. By the time it's warmed up, it's already overheating. The gauge goes past 220 and then keeps moving toward the red zone. I am unable to drive more than a few miles before having to pull over.
The overflow reservoir overflows a bit, but then goes back down when cooling off. I run the heater at full blast, but the air doesn't feel hot. The oil appears normal in color, so I don't think the block is cracked or the head gasket damaged.
Any ideas what might be happening here? I know many are going to say I should have gone with Mopar, and you're right about that. Even so, the TJ should be drivable regardless, even with a slightly higher engine temp. I am in the PNW, and we are seeing temps in the 70-80 degree range. Overheating in this weather must be due to something more than non-OEM parts.

Install a Mopar thermostat. Drill a bleed hole in the flange beside the jiggler, hole goes at 12 o;clock. Report back.
 
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TexasTJ2004

I love my TJ
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Also, making an exhaust gas in coolant test might be a good idea. It is 30$ test, and it will make sure that the overheat is not related to the exhaust mixing with coolant.
 

Ericshere03

TJ Enthusiast
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Apr 8, 2019
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Feenicks
Install a Mopar thermostat. Drill a bleed hole in the flange beside the jiggler, hole goes at 12 o;clock. Report back.

I keep seeing the Mopar thermostat suggestion, they’re just a Motorad these days. I’ve had a few Motorads and they have all been unstable. Stant superstats have always provided stable temperatures but were always a pain to get. But now stants are Motorad (bought out)… I’m in Phoenix so we tend to get toasty here.

Motorad may have a more premium or higher quality SKU for OEMs , but I sort of doubt it. Then again, Motorad might have inherited Stants quality (Superstat at least)

Regardless, I have a new Jeep with a unstable needle, runs 3/4 to 210, sometimes just below the 210 dot (which is normal) and sometimes at the 0 part of 210. I’ll be experimenting with thermostats again to find a suitable replacement.
 

mrblaine

Crew Member
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Nov 20, 2015
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Quail Valley, CA
I keep seeing the Mopar thermostat suggestion, they’re just a Motorad these days. I’ve had a few Motorads and they have all been unstable. Stant superstats have always provided stable temperatures but were always a pain to get. But now stants are Motorad (bought out)… I’m in Phoenix so we tend to get toasty here.

Motorad may have a more premium or higher quality SKU for OEMs , but I sort of doubt it. Then again, Motorad might have inherited Stants quality (Superstat at least)

Regardless, I have a new Jeep with a unstable needle, runs 3/4 to 210, sometimes just below the 210 dot (which is normal) and sometimes at the 0 part of 210. I’ll be experimenting with thermostats again to find a suitable replacement.

I can only do what I know. What I know is I've installed 50 or 60 Mopar thermostats, I have 100% success with them. You do whatever like, if I work on a cooling system with a deficiency, I know how to solve it.
 

Ericshere03

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I can only do what I know. What I know is I've installed 50 or 60 Mopar thermostats, I have 100% success with them. You do whatever like, if I work on a cooling system with a deficiency, I know how to solve it.

To be clear, you are saying that the Mopar flavored Motorad thermostat has a 100% success rate? Does the Mopar Motorad have a giggler valve ?

Stant was an OEM, my guess is Mopar was a Superstat. Now the Motorad ultrastat is the new Superstat )and Mopar thermostat). My experience with Motorad was before the a acquisition of Stant. Perhaps the Motorad is indeed equivalent to Stant now a days.

I might have installed half as many thermostats in my 20 years of driving experience, but I have never had an issue with a Superstat on a Jeep, Vette, Z, Yota 4x4/car … I “baseline” every used car get, all fluids, thermostat, plugs, plug wires, cap n rotor, etc.

As usual I overthought the simple. First question a mile up my message is the only thing that matters.
 

mrblaine

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To be clear, you are saying that the Mopar flavored Motorad thermostat has a 100% success rate? Does the Mopar Motorad have a giggler valve ?

Stant was an OEM, my guess is Mopar was a Superstat. Now the Motorad ultrastat is the new Superstat )and Mopar thermostat). My experience with Motorad was before the a acquisition of Stant. Perhaps the Motorad is indeed equivalent to Stant now a days.

I might have installed half as many thermostats in my 20 years of driving experience, but I have never had an issue with a Superstat on a Jeep, Vette, Z, Yota 4x4/car … I “baseline” every used car get, all fluids, thermostat, plugs, plug wires, cap n rotor, etc.

As usual I overthought the simple. First question a mile up my message is the only thing that matters.

Dig around, there are 50 examples of aftermarket products to replace the OEM versions that are simply not up to snuff. O2 sensors to radiators and practically everything in between are just not the same when it comes to the TJ. Again, do what you like, I'm going to keep doing what I know works every single time.

As for who makes the Mopar thermostat, I neither know nor do I care.
 

Ericshere03

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Dig around, there are 50 examples of aftermarket products to replace the OEM versions that are simply not up to snuff. O2 sensors to radiators and practically everything in between are just not the same when it comes to the TJ. Again, do what you like, I'm going to keep doing what I know works every single time.

As for who makes the Mopar thermostat, I neither know nor do I care.

Right, “do what works”, got it … my recipe was Superstat … that option is now toast … in your experience, have you used the Mopar thermostat that’s branded Motorad? And did it have a juggler valve like they used to? I am trying to figure out it Mopar is in fact a different Motorad than store/Amazon motorad.

And I get it, OEM/Mopar is best (I have Mopar water pump, hoses, hose clamps, thermostat housing, etc) but then Mopar sells out to the lowest bidder and we pay a premium for the same chineesium garabage I can get for 5 bucks at autozone, kinda feels like I am being bent over a barrel. That’s what I felt last time I bought a Mopar thermostat from the dealer and saw a Motorad inside the bag. Luckily I found a genuine USA made Stant at that time and replaced it(a few years ago). That time my Jeep ran too cool, sometimes, I didn’t like the fluctuations. OEM never “fluctuated” and neither did the Stant.
 

Ericshere03

TJ Enthusiast
Supporting Member
Joined
Apr 8, 2019
Messages
230
Location
Feenicks
Dig around, there are 50 examples of aftermarket products to replace the OEM versions that are simply not up to snuff. O2 sensors to radiators and practically everything in between are just not the same when it comes to the TJ. Again, do what you like, I'm going to keep doing what I know works every single time.

As for who makes the Mopar thermostat, I neither know nor do I care.

Dig around, there are examples of OEM being junk or at best Vato Zone equivalents… OPDA (low blow, I know), spark plugs (just NGK).
 

MichaelGH

Hemi ‘97
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Jan 19, 2021
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OHIIIIIIO
Not that you should but there are thermostatically controlled transmission cooler bypass valves specifically made for that problem. They circulate the fluid back into the transmission until it gets warm enough to open the bypass which then shunts it through the cooler and then back into the transmission.

This is exactly what I run on my TJ. I do not go through the radiator at all. Straight from the transmission, then into the bypass and then onto the auxiliary cooler. I run a 145° Opening thermostat that is fully open by 163° (FSM-145). Works flawlessly for my 545RFE. Makes the transmission warm up properly in the Winter and allows the cooler to keep the fluid reasonable in the Summer. On the hottest day I don’t think I have gotten the fluid temp over 180-185 even sitting in the slowest traffic on some seriously hot days. Usually it hovers 145-150°…


https://www.improvedracing.com/high...HCiPUm5fxd-olaY4fopQlMhCZtmfFzSAaAtNvEALw_wcB
 

radiationfool

New Member
Joined
Jul 24, 2022
Messages
3
Location
Washington

I tried observing the coolant with the radiator cap open while starting with a cold engine. First I topped the radiator off with water until I could see the water, then started the engine.
At first everything seemed normal. As it warmed up I started to see a few bubbles coming up, but very little overflow. Then it got up to operating temp and seemed okay for a very short time. Suddenly it started to spew like a geyser, and the temp shot up to the redline. I shut it down immediately, and could hear loud "boiling" noises in the engine block.
I'm afraid that the head gasket is allowing exhaust into the cooling system, and read that this can happen after severe overheating.
Any opinions?
I'm probably taking it to a local shop if this is the case.
 

MichaelGH

Hemi ‘97
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Jan 19, 2021
Messages
708
Location
OHIIIIIIO
I’ve never owned an automatic Jeep, but is this a real problem? The Trans fluid needs to be heated? I’m ignorant to this for sure.

Would letting the Jeep sit and idle like I have to on this CJ 304 do the trick?

You said “ not that you should” so I assume you wouldn’t necessarily. Is this a solution looking for a real problem?

Like an engine, a transmission works well/best inside a certain temperature range. My 545RFE functions normally between 80-240°. Any colder and it will not shift per usual to protect itself from damage. Any hotter and you are starting to cook the fluid which will in short order cook the transmission. Automatic transmission fluid does not like to be ran too hot, even synthetic. It looses its properties and cannot do the job its needed to…
 
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TexasTJ2004

I love my TJ
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I tried observing the coolant with the radiator cap open while starting with a cold engine. First I topped the radiator off with water until I could see the water, then started the engine.
At first everything seemed normal. As it warmed up I started to see a few bubbles coming up, but very little overflow. Then it got up to operating temp and seemed okay for a very short time. Suddenly it started to spew like a geyser, and the temp shot up to the redline. I shut it down immediately, and could hear loud "boiling" noises in the engine block.
I'm afraid that the head gasket is allowing exhaust into the cooling system, and read that this can happen after severe overheating.
Any opinions?
I'm probably taking it to a local shop if this is the case.

Buy this kit Block Tester BT-500 Combustion Leak Test Kit - Made in USA https://a.co/d/2eCEUEH
It is 36$ now.
Run the test, it takes 20 minutes and you will know whether you have exhaust in coolant.
I am planning to do the same, as keep seeing bubles, and I don’t expect to see any.
 

cpwolf

Armed Texan
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Joined
Jun 15, 2020
Messages
1,047
Location
TEXAS - Cedar Park
The thermostat that came in my '97 TJ purchased new was not a SuperStat. I know that thermostat well, I recommended it for years.

Do you not anymore? Dammit, ha, I literally just put one in before this thread. It’s working, so I’ll go with it, but won’t be next time. My maintenance book will have a scratch out of a recommended part now, messing with my clean notes, ha.
 

Jerry Bransford

TJ Guru Moderator
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Nov 9, 2015
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Fleming Island Florida
Do you not anymore? Dammit, ha, I literally just put one in before this thread. It’s working, so I’ll go with it, but won’t be next time. My maintenance book will have a scratch out of a recommended part now, messing with my clean notes, ha.
I shouldn't have implied I no longer recommend it. For all I know the SuperStat hasn't changed after Stant was purchased by Motorad. As already mentioned just because a company is purchased doesn't mean what they make changed.
 
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