Edit: Thermostat starts to open by 195* by design. But it is a restriction to flow in the system, also by design. Most thermostats, when at design operating temperature, are about halfway open.

There is heat being built in the engine, and the transmission, continuously during operation. It is not instantly removed by the radiator, exhaust system, and by radiation to the atmosphere.

At 210*, the system is in equilibrium. This is also by design. That 210* temperature helps combustion to be more efficient and complete, helping power and fuel mileage.

Now if the engine overcools, the thermostat starts closing. This helps keep more hot water in the block, away from the radiator. This will help the system regain equilibrium.

Think about this for a minute. If someone removes the thermostat, and the outside temperature is 70*, does this mean the engine will never warm above 70*? No, it'll run about 140-150 or so. That's too cold for the engine operating temperature. The system creates more heat than it can throw away at the same time.

Power and efficiency go down, and sludge starts to build.

 

Actually, a stat begins to open at it's rated temp. It is not fully open at it's rated temp. A 195 stat starts to open at 195 and will be fully open, or close to it, at 210. In cold weather and using the heater, even the XJ cooling system will maintain coolant temp at, maybe even slightly below the t-stat rating due to rapid heat loss in cold weather. The stat rating/open temp is the equilibrium temp, not 210.

Using a ScanGauge for 4 years now, I can just about guarantee coolant temp this time of year in a properly functioning cooling system is not going to actually be 210, like the rigged factory gauge displays.

 

i have been using a 195 stant tstat for about 8 months and/or 15k miles. it functions correctly and always has. bear in mind the sending unit is in the back of the head. coolant in that portion of the system is hotter than what the tstat is seeing. I took an ir temp gauge to both areas. the tstat housing held steady around 178-185 while the back of the head was showing 195-200. the needle in-dash was showing one notch left of 210, where it typically lays. this was full operating temp after driving 20 miles (30 minutes) and it had idled for 5 minutes or so while I messed around with stuff, ambient temp was in the 40s - overcast skies.


something that might be worth mentioning - when my fan clutch failed this winter, I noticed full operating temp was holding steady around 210 unless I was moving, in which case it went back down to the first notch left of 210. this was abnormal for my jeep. after roughly 25 seconds of diagnosis I figured out the fan clutch no longer worked.


edit: for those of you wondering, I took the ir temp gauge to the exhaust and various other items haha. manifold coming out of the head showed 490-530 and 280-300 at the cat. not sure what to make of it, but the area before and after the cat (including the converter itself) ranged from 280-300. I thought the catalytic converter should be hotter than the exhaust before/after it? just an observation, I'm fairly certain the exhaust on this thing is stock as it has more rust and holes in it than anything else. the cat is literally falling apart...but I think most of that was caused by the xfer case output shaft seal leaking for god knows how long and throwing gear oil all over it, creating a terribly obnoxious smell amongst other things.


in the summer with that tstat and a functioning fan clutch the needle would lay comfortably between 210 and the notch to the left. it rarely saw 210, especially if I had the ac on. that little elec fan is surprisingly efficient.

 

IR temp guns/gauges can give somewhat inaccurate readings based upon the metal it's pointed at and the color of the surface it's pointed at. In other words, a reading taken on a black iron head may be different than a silver aluminum t-stat cover. Theoretically, coolant exiting the t-stat cover should be the hottest because it's been in the motor the longest.

Mathematically, the mark below 210 is 182.5 which seems a little low when using a 195 stat.

 

I chased a funky temperature surge in my XJ for a few months... After replacing the entire cooling system and popping in a stant.. she stands at 200 degrees and will not budge.

I know anything but OEM has a bad rep... But the stant (no jiggle valve) is holding up quite nice. I will let you guys know if I have any failures from it.

I hate aftermarket for some parts.. but the stant just seems to be IMO a pretty solid thermostat.

 

Exactly opposite of my experiences on our family's 3 Jeeps.

 

None of them seem to last more than a year in my experience. Now use a Jegs inline thermostat housing, which makes the replacement process so much easier. And can use Chevy thermostats which seem to last twice as long.

 

Isnt it crazy? I had the stant on my parts shelf before I read about others experiences. But when I did that cooling overhaul, I decided to give it a try... Since its a few minutes to replace it anyways. It has been solid!

 

I think coolant nearest the heat source would be the warmest, but whatever I'm not here to debate heat transfer physics.





this is where the needle lays 99% of the time. I think accuracy of the dash gauge is certainly in question. none of the other gauges are very accurate. volts at the battery by use of a multimeter show +0.5-0.75 over the in-dash gauge, as well as the oil pressure - a mechanical gauge shows +10-15 psi (rpm dependent) vs the dash gauge. i'm not attempting to start a debate or spread bad info, simply trying to find a base for universal comparison, as not everyone checks their vitals with real instruments.

 

I'm not debating anything......cooled coolant enters the front of the block, travels the length of the block, then exits the block at the rear where it then enters the head at the rear of the head and travels the length of the head back to the front where it exits the head via the stat housing.

All I'm saying is coolant at the back of the head hasn't been inside the motor as long as coolant that is exiting the front of the head. Coolant exiting the front of the head most likely is warmer because it's been in the motor a little longer than coolant at the back of the head.

U r absolutely correct to question the accuracy of the gauges.....especially the temp gauge.

 

Check this out.

 

I put in a murray? Stat from orielys about 6 months ago. I messed up and got a 180 degree stat. Ran about 180 in the summer and is now running around 155 on 50 degree days. I think its not closing all the way I'm not sure. But I'll be getting a 195 oem from jeep this weekend and I'm sure my jeep will be much happier.
Just throwing this out there

 

Excellent plan. 52028186 at the dealer.

 

See after replacing my dealership stat I sit where you are. Can cruiser confirm this is right or wrong? I know people say 210 but even my dealership stat and the one before when I bought it, stay at what is pictured and just below the 210 notch

 

I have older Jeeps and gauges are different. djb383 is the "whiz" on needle position.

Gee, that doesn't sound very complimentary, does it?