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What temp t-stat?


NAXJA Forum User
I have an 88' with the 4.0. I have a Jet t-stat in it now. I think it's 180 degree. Is this okay to run? Or do I need a 185 or 195 degree. Also what is the best one to use? Thanks Juice
The design operating temp for a 4.0 is about 210 degrees F, give or take 5 degrees. To help achieve that temp as quickly as possible, the AMC/Chryco engineers specified a 195 degree thermostat.

I would not recommend anything but that 'stat. Not only will it NOT make your XJ run any cooler, but it will actually upset the optimal emissions control during the warm-up cycle.

Run the 195.
Seems that the D/C OEM tstat is built at least as well as the other, and has an air bleed valve that the aftermarkets don't.
Agree with ChiXJeff. The air bleed hole in the flange helps prevent air pockets. Although some t-stats in Pep Boys have a hole in the flange, I have never found an aftermarket one listed for the XJ that has it. For that reason, I only buy t-stats from a Jeep dealer.
CheapXJ said:
I get the stant HD ones, and drill a hole in the flange.

saves time, aggravation and $$$

I agree. I know that the OEM one from Chryco is going to be a perfect fit, so to speak, but there is no reason that an aftermarket thermostat cannot be used, PROVIDED an air bleed hole is ADDED BY DRILLING.

The XJ is NOT the only car ever made that needs these air bleed holes in the thermostat. I have drilled many a thermostat to add these holes as necessary, and it works just fine, as long as you orient the hole correctly.
I don't know if the stealership has an OEM one like it, but I will not run anything but a fail safe (when it fails it sticks open instead of closed) type. It runs a few $$ more, but it's cheaper than an engine rebuild caused by overheating. I just drill a 1/8 hole in it (I think they have a valve in them now) and then I don't need to "burp" the sysyem.
I am a bit confused by your response are you suggesting that the dealer ones are not fail safe ?? Are the Hi-performance ones superior to the standard dealer ones in flow ? Whats the benefits of each..what do ppl on the forums suggest ?

All of the OEM's that I've had fail, got weak and caused the engine to run cold. But I have had (aftermarket), fail mostly closed, especially if the engine has overheated once. They then get unreliable.
Whatever you get, make sure you get the right gasket and don´t try and use a universal gasket.
If you have reduced flow, a colder thermostat isn't going to help much, it's usually from stuff, partially plugging the bottom of the radiator. Increased air flow, seems to help more than increased coolant flow, in most instances anyway.
I did run a 185 for awhile, which really didn't seem to help much in keeping the temperature down (stuck in traffic), it mostly affected the heating in the winter and made for a long warm up period. I also ran a 192 for awhile, that worked well. Putting in a switch, to turn on the aux fan early, cured my slightly high temps, while sitting in traffic and low gear Wheeling.
The one i have is about 3 yrs old (mopar/dealer 195) and i suspect that it is opening a bit delayed. I say this becuase when i first start the jeep it goes all the way to about 215-220 and then all of a sudden goes to 195-200. I have a thread about getting warm in traffic which i think this stat issue be related. I have practically replaced everything else (rad, water pump, fan clutch). If i replace it i dont on planning on using any other temp other than 192/195 bc i dont want to mask the problem if their is one. I am just curious on what stat to use, i have heard that the stant high perf ones open and provide much better flow but i also heard of high failure rate from third party stats.

People forget, the thermo isn't usually fully opened or closed, it is constantly changing position (trying to keep a constant temperature). High flow would only be helpful, it seems to me, at full open (if I remember correctly full open is somewhere around 219 at the thermostat).
People also forget, the temp Gage sensor is in the top rear and the thermostat is in the front (probably fairly different temperatures). There is gonna be some hesitation, in one catching up to the other. And the engine temp sensor for the ECU, is in the bottom of the block, near the radiator outlet. Running much below, recommended temps at the gage, is probably causing the ECU to run a bit rich, due to the lower coolant temp. at the ECU temp. sender.
Hey 8mud i never said about running a cooler stat.

You said a high flow stat would help at temps around 219 (full open), so wouldnt that be overall helpful ?

jeepsrock said:
Hey 8mud i never said about running a cooler stat.

You said a high flow stat would help at temps around 219 (full open), so wouldnt that be overall helpful ?


Possible a bit, but the restrictions seem to be more prevalent, at other spots in the system (like the bottom of the radiator, in an old unit). Surface area of the radiator (layers) seems to help some, but the greatest boon in my experience is with increased air flow. Possibly turning the pump at a higher RP M's (smaller pulley?) to increase flow could be a benefit at low RP M'S, low flow does seems to be slightly apparent at low RPM´s in my XJ's.
Just a theoretical thought or two, the object is to move excess heat, from the inside to the outside of the motor. Increased surface area in the heat exchanger (extra layers can do this), moving more air through the heat exchanger can do this. But it´s doubtful moving more coolant through the heat exchanger, by increasing flow at the thermostat, is gonna help much (pump RPM, would seem to have a larger influence anyway). The efficiency of the heat exchanger is the temperature drop between the inlet and outlet. The coolant rarely gets all the way down to anywhere near air (ambient) temperature. So pushing the coolant quicker through the exchanger isn't actually gonna do much, if it actually works, the thermo is probably gonna slow down the flow anyway. If it pushes the coolant through before it has time to loose maximum heat, it will actually exit at a somewhat higher temperature, it doesn't exit at anywhere near ambient (air temp) anyway.
Fine tuning the system, with a high flow thermostat, may have a benefit, but it´s doubtful, the benefit would be where it could be used. At higher RP M's on a fairly hot motor. I´m just skeptical of the benefits.
Air flow, surface area and pump RP M's (flow) would seem to be more important than a possible restrictions at thermostat full open temperatures. If there was actually a restriction in that area, the top hose would probably have a tendency to collapse.
I think high flow thermostats, may be holdover from the old Chevy's that seemed to benefit from increased coolant flow (around the thermostat and elbow area). But guys did take that too far also. They would remove the thermostat all together and at sustained high RPM´s the system would push the coolant through the radiator, before it could give up much heat and this would actually cause higher engine temperatures. Until the system stabilized, if it ever did.
Most of this is just theory, I´m not an XJ cooling guru, but have worked on a few building sized systems.