BDGile

Lets settle this once and for all. I have read hundreds of posts in dozens of threads that declare very strong opinions on this topic. What t-stat do you use, and why?

Diesel

195, its OE.

Only reason to put in a 180 is if you put a 3 core in as well to run lower temps. if not, stay 195.

00jeepXJ

People use the 180 to run a little cooler. I just run the stock 195 because that is what the engineers and factory uses. Also you need to know that if you run a much cooler then stock thermostat you can cause your engine to run too cold for what it was meant. That is my two cents.

2Evil4U

The key is cooling capacity. If your rig constantly runs between 210 & 220 with a 195 stat, installing a 180 will not change anything other than the temperature that the stat opens and allows coolant to flow through the system. If you can honestly run at the rated temp of the stat, then a lower temp stat may allow you to run cooler, if and only if, you have the additional cooling capacity to eliminate the required amount of heat.

These things are not set up to cool very well unless the cooling systems are immaculate and properly maintained.

argyll1984

I would have to think that if it was better for the motor to run cooler, than it would have come from the factory with a 180 t-stat, so I stick with the 195. If someone can give me a comprehensive explanation of why a 180 t-stat would be better I'm all ears.

djb383

All of the high performance catalogs/publications list 160F and 180F t-stats....never seen a 195F performance t-stat. Everything in the 70s, 80s and 90s came with a 195F t-stat, higher engine temps was a cheap/easy/quick way for reduced tailpipe emissions but not necessarily the best thing for engine performance/longevity. With improvements in electronics, engine management systems, injector spray patterns, heated O2 sensors, larger surface area single row rads, lower temp factory t-stats, etc., etc., etc., todays tailpipes run cleaner with reduced engine temps. The factory t-stat in our '06 Saturn V6 is a 170F, as an example. Been running a 180F t-stat in our '98 XJ since December (installed it shortly after we bought the XJ).....the heater works plenty good and we consistently get mid teens city mpg, low 20s highway mpg.

Put a man on the moon in 1969 and 15-20 years later Detroit was still giving us carburetors.

argyll1984

Those are some good you make. I might have to look into it a little more.

Bustedback

195 because the guys in the white lab coats thought it was the best to run. They have far more schooling than I do, so I'll do what they thought was best.

Dugualla

The computer controls are optimized for 195 stats, and run consitantly around 210. That is all there is to it. Colder stats will not increase the cooling capacity of your cooling system. The stat isn't even a cooling component, it is a heating component, it disables the cooling system until a certain, preset tempurature is reached.

Diesel

.

Refer to my post. Only reason to put a 180 in, is if you plan on running something like a 3 core to run colder temps.

sandaddik2

i run 180 because i dont like over heating when driving to big bear

Diesel

The engine would be getting a signal from the Coolant temp sensor that its not warmed up and it will continue to run a richer fuel mixture, wasting fuel with the 180.

Dugualla

I understand your point but I do not see the reason for running cooler temps. The process controls are tuned to a certain percentage of 02 at a certain tempurature, changing either perameter defeats the tuning IMHO. I say, do what it takes to insure the engine runs in the prescribed range of 210 to 220 in the conditions it is drivin in. If you do allot of wheeling and low speed driving a 3 core radiator or additional electric fan may be neccesary to maintain 210 but a colder stat isn't the answer.

I just reread your post, seems we are in complete agreement with the exception that I see NO reason to run colder than 195. I do see where hours of 5mph driving with no airflow in the desert may require more cooling capacity (which is no way related to tstat range).

Diesel

^^^

Logical thinking from someone, finally.

Your engine has a PCM (power control module) that monitors fuel delivery and emissions controls. The primary O2 sensor (located just aft of the exhaust manifold) is monitored during “open loop” while the engine is warming up. There is much mythology that use of a thermostat lower than 195 degrees will not allow the engine to go into “closed loop” mode, delivering much more fuel. Engine power is a function of the fuel/air ratio (among other factors) and PCM monitors and regulates that ratio. However, the 4.0L engine will go into closed loop very quickly and at a low temperature. However, the advantage of the 195 degree thermostat has to do with efficiency and this engine is more efficient, and obtains better gas mileage at a higher operating temperature than many in the past, i.e. 210 degrees. This is why in most applications, the 195 degree thermostat is the better choice"

djb383

See what u got started, it can't be settled once and for all. What I'd like to see settled once and for all is no more references to the number 210 IF the reference is based solely on what the factory idiot gauge displays. With the dinky radiator (small surface area) that the XJ was born with, there's no way actual coolant temp is 210 in both the middle of winter and the middle of summer.