You're absolutely right about a t-stat controlling when coolant is allowed to flow to the rad or controlling the minimum temp when coolant is allowed to flow. If the rads big enough and the t-stat's open/close rating is below 180F, coolant temps will be below 180F. Diesel engines run cooler than gasoline engines in fact, during cold weather diesel engines may struggle to produce sufficient cabin heat. You always see the big rigs with the grille covers on during winter.

Have you ever placed a t-stat in a small pan of water on top of a stove with a cooking thermometer and heated it up? If you have, you will have noticed that a t-stat is extremely slow to open and extremely slow to close......in fact, you may have a birthday between the opening and closing event. LOL The t-stat mechanism only moves about 1/4" from closed (it's temp rating) to wide open (about 15-20 degrees above it's temp rating). If actual coolant temp (not what the factory idiot gauge displays) is 210F, then a 195F t-stat will be at/or almost wide open. A 180F t-stat and a 195F t-stat open the same amount, about 1/4", (just at different temps) and BOTH flow the same amount of coolant when wide open. There's an infinite number of open positions up to about 1/4". When the t-stat is wide open it's doing nothing, it's done all it can. It only controls minimum operating temp.

Cool ambient temps (fall, winter, spring), an automotive t-stat will vary from closed (not water tight) to just barely open. Summer time, at least for the XJ with it's dinky radiator, is probably wide open most of the time the engine is on. To say coolant temps reach 240F with a 180F t-stat but only reach 190F-210F with a 195F t-stat..........I think there's several more variables at work than just different temp t-stats.

 

ACTUAL coolant temp does vary (up/down yoyo), more so during summer time hot weather and less in cool weather. Most factory idiot gauges don't show the coolant variances........they rise to the middle and basically sit there. The least amount of coolant temp variance will be at steady cruising/highway speeds on level ground.

 

There was absolutely no change other than the tstat. Clean rad good hoses and no overheating problems before the 180...a friend asked what degree it was and suggested i try a 180 so I did and it ran at 240 constantly...so then swapped back to the 193 or 5 whatever it is and things went back to normal.

 

It's a 195F. Did u test the 180F t-stat in a pan of water on top of a stove with a cooking thermometer? New t-stats have been known to be bad and stick closed. I would never install a t-stat without testing it 1st.

 

It was tested. I have also bought many bad tstats. Look I am not saying that a lower tstat doesnt help some vehicles but in the 2 that I own(cherokee and mustang gt) they do not.

 

Have 185 in my 96 runs 188 to 196 most of the time. but i dont trust the factory gauge so i watch my scan gauge also run 70% distilled water to 30% coolant. just what i do

 

I have been running a 180 in my 95 and have never had no problems i rather do that then replace a head gasket or better yet the engine over heat lock up i've seen it happen specially on the trail let see twice the work and half the air coming in because your not moving that fast OH YEAH GET THE 180* THERMOSTAT!!!!

 

I never said anything about a lower temp t-stat helping anything. All I've said is "the sole purpose of a t-stat is to control MINIMUM coolant temp". But I also say there's no way a properly functioning 180F t-stat would be the SOLE cause (no other variables such as different ambient temps) of coolant temps being 30-50 degrees higher than coolants temps when using a 195F t-stat.

As I said before, when coolant temp has reached 210F, BOTH a 180F and 195F t-stat are open the same amount and allowing the same amount of coolant to flow to the rad. Once t-stats are wide open, the only thing controlling coolant flow is the water pump and condition of the cooling system (dirty equals more flow resistance).

 

yeah i under stand that but the 180 will begin to cool the egine block faster then the 195 i have a 180 on mine and my coolant temp never hits 210

 

Is that the factory temp gauge that never hits 210F?

 

no its not because my cooling fan went out and it went past 210

 

Running a colder thermostat isn't necessarily going to lower your operating temps.
In fact it could cause poor performance as the computer switches from open loop to closed loop when certain parameters are met (including coolant temp).
Without diving into the computer and figuring out what that temp is I couldn't tell you for sure if it would delay the switch or not.


There is a different reason you switch to a cooler thermostat.... the heat starts working a little quicker.

 

i hate to argue but i see it everyday when i drive the jeep it runs cooler then before when i had the 195 in it

 

here is a good article about running cooler thermostats

http://hotrodscott.blogspot.com/2007...ermostats.html


if you want your motor to run cooler a simple mod is to have an over ride switch to the electric fan and keep it on.
Still... even though these Cherokees are not nearly as advanced as new cars are they still use computers to help control much of the functions of the car including temperature of the engine.

My operating temp went down when I flushed the cooling system. I don't credit the antifreeze type for the lower temp.

I'm not saying there isn't a reason for a cooler then OEM thermostat just that there is no magic. It isn't an upgrade or hopup for these newer vehicles, as much as it is a component for necessary engine tuning.

EXAMPLE:
I put a cooler thermostat on my Camaro because having an electric water pump and an over ride switch I can put the car back into open loop when I start the car back up. This is after a computer tune. Between runs I try to keep the temp between 170 and 180 and the stock thermostat kept closing, this prevented me from cooling the engine block to the desired temp.

 

Running a lower t-stat will lower operating temps IF outside ambient temps are low.......this time of year, it's highly unlikely that a lower t-stat will lower operating temps.

It's simply a myth, that keeps getting perpetuated on the Internet, saying the engine coolant must be at operating temp before the system will enter "closed loop". When the upstream O2 sensor reaches operating temp (600F-650F), less than a minute after engine start-up, the system enters "closed loop. As you can see in this pic, the system has entered "closed loop" and coolant temp is only 94F.

Are you saying that the heater starts working a little quicker with a cooler t-stat???????? Don't see how.