A wide open t stat will flow just about what the pump will max flow. Wouldn't be very difficult to design a t-stat that would open twice as much.....but it's just not needed due to the water pumps capacity. Besides, u wouldn't wouldn't want the t-stat to open too much, that would almost be like having no t-stat thus causing overheating driving down the highway. LOL

The t-stat is in there as a restriction to control MINIMUM coolant temp.....when wide open it is not a restriction beyond the pumps capacity.

 

I wouldn't run with out a t-stat it's gonna kill your engine sooner. I actually thought the cooler your engine ran the better. I asked my automachanics teacher about it and he said your engine was designed to run warm with out one or a lower one they run less efficient. This means worse gas mileage and performance. I recently changed my t-stat from 165 to the stock 195 and I'm already seeing an improvement.

 

what does it being an OBD2 have anything to do with it?

 

OBD-II will set a CEL if a heat cycle is not reached (160F). As soon as the heated O2 sends info to the ECM, the system will enter closed loop, well before 160F coolant temp is reached.

 

Scenario; You park your operating temp, (or near),engine with no T-stat. Go in the store for 15 minutes, come out and start it. Now cold water in the radiator rushes into your (still hot) engine. Guess the 4.0 can stand that, at least some. Not a nice thing to do to an engine, dumping cold water in it while it's hot.

 

Having experienced this in multiple vehicles, running without a thermostat WILL make a vehicle overheat. It may take a long time for the temp to build up, but it WILL happen.

Ive owned 2 thirdgen camaros, an s10, and now this cherokee. All come from the factory with barely adequate cooling systems.

The thermostat DOES control the operating temp range for the motor like you stated, but that is a seperate and irrelevant issue.

The cooling system transfers heat from various parts of the motor into the coolant and them transfers that heat into the air at the radiator. If the water is constantly flowing without restriction, it CANNOT adequately remove heat from the engine and take it to the radiator.

YES, the temp guage will read cooler, but only because it does not have enough time to absorb heat in the motor. The motor WILL run hotter. Which can only be verified by checking the temps of the heads/block/other parts. The guage in the dash is not an exact measurement.

Feel free to run a lower temp thermostat, but DO NOT DO NOT DO NOT DO NOT DO NOT run without some sort of thermostat.

If running without restriction was such a great idea, they would use it in racing vehicles. NASCAR cars dont use what we use as a thermostat, but they do restrict coolant flow somewhat to more efficiently cool the motor.

 

When's it going to overheat without a t-stat.....August or January?

 

It will in both if it runs long enough under the right conditions. Coolant has to spend enough time in the block to gather heat and spend enough time in the radiator to expel said heat.

Just because the coolant guage says 160* and the coolant isnt spewing out from the overflow DOESNT mean you arent overheating the MOTOR.

I ran my camaro with no thermostat. Rest of the system was in 100% operating condition (newer h2o pump, radiator, fans working, hoses good, etc.) Overheated in freezing temps and overheated even quicker in hot temps.

Put a thermostat in it and the problem went away.

 

Temps of 150 ish running down the highway at 75mph at 2400rpm or so. Anything below 55 would creep the temp up to 220+, 250+ sitting in traffic in the heat.

 

Whatever...............might want to re-read the links I posted.

 

If the thermostat needs to be replaced, install one
with the same temperature rating as the original. Most cars and light
trucks since 1971 require thermostats with 192 or 195-degree ratings.
Using a cooler thermostat (160 or 180 degree) can increase fuel and oil
consumption, ring wear and emissions. On newer vehicles with
computerized engine controls, the wrong thermostat can cause major
performance and emission problems if the engine fails to reach the
proper operating temperature.


Quoted directly from your link.


It is not advantgeous to run our cherokees without a thermostat, or even with a lower temp thermostat.

Case closed i guess.

 

Simply stating my experience with running without a thermostat. No matter what way you look at it, running without one is not a good idea.

 

Amen

 

dang... i just was curious about it.

 

Would u mind re-reading post #9 in this thread......think it was the 1st post to reference to "don't operate WITHOUT a t-stat".

Nowhere does it say in the FSM a 195F t-stat is "required".