Topic: Can I run a cooler thermostat?

[tj.gator]

Greetings

I was wondering if there is any benefits to installing a cooler thermostat in my Jeep.  On previous cars it seemed to help but with the computer running the show it required a modified ECU chip.  Has anyone installed a 180 degree thermostat and what if any modifications or benefits went along with the change?  It's pushing 100 degrees outside every day here now I would think every few degrees you can cool the cylinder head down will help.  Thanks in advance for any input.

[Jeffy]

Changing the thermostat won't drop the running temperature.  Once the thermostst is open, it's open and will climb to the same temp.

[tj.gator]

Correct me if I'm wrong, but that would only apply if the cooling system was cooling at maximum capacity.  If an engine has an undersized cooling system then the thermostat will be wide open trying to let as much hot water as possible go through the radiator to try to get down to the setpoint.  Conversely if the same engine has an oversized radiator and fan then the thermostat is going to stay closed more often to try to maintain the water temperature at the setpoint.  I am assuming of course that my electric fan and radiator are capable of maintaining the 180 degree setpoint.

[Jeffy]

Correct me if I'm wrong, but that would only apply if the cooling system was cooling at maximum capacity.  If an engine has an undersized cooling system then the thermostat will be wide open trying to let as much hot water as possible go through the radiator to try to get down to the setpoint.  Conversely if the same engine has an oversized radiator and fan then the thermostat is going to stay closed more often to try to maintain the water temperature at the setpoint.  I am assuming of course that my electric fan and radiator are capable of maintaining the 180 degree setpoint.

Since the engine is designed to run at a normal 210* it will climb even with a 3 core radiator.  I doubt you'd be able to get a radiator that's large enough to keep the temps that low.  (You'd need to cool the oil as well among other things.)

The other down side is that if you live in a cold area, the engine might have trouble since it will never get warmed up enough.  You'd probably also see your gas mileage drop off as the engine things it's cold all the time and will increase the air/fuel mix to compensate.

I ran a 180* for a while but noticed no difference.  I went back to the 195* but with a performance thermostat which is more accurate.

[Jesse-James]

Mine came with a cooler thermostat, It didn't necessarily run cooler just had huge temp variation. It would eventually get close to 180 then climb up to 210 or so. Temp was all over the place.

[tj.gator]

That was the original intent of my message.  I have played with the thermostat in my Jeep and if you cut the spring so the thermostat stays open the engine will run around 175-180 degrees on a 90+ degree Florida afternoon.

The temperature variation you see is the thermostat opening and closing.  As it opens it allows more water to flow throught the radiator and the temperature drops to the setpoint (180, 195, or whatever).  When the thermostat begins to close the temperature climbs again.

Using the calculations for volumetric efficiency on our 2.5's if you drop the operating temperature by 20 degrees you should see a HP increase of about 4% which would be roughly 5HP on mine.

The problem, which was the original intent of my post, is that most ECU's have a temperature that they want the engine to operate.  If it expects to see 210 degrees and you are only at 180, then it makes the engine run rich to "warm-up".  I am interested in seeing if anyone has had success in changing anything to "trick" the ECU into thinking it's at the proper temperature.

I suppose if nothing else I can put the 180 degree t-stat in and build an AFR meter and use the adjustable MAP sensor to try to compensate and see what happens but on a lot of OBDII ECU's it's not that simple because in "warm-up" mode it changes ignition and other things.  Sorry this is so long.  Does anyone have any input on the ECU questions?

[/dev/null]

My 'other' car is a '96 Tbird with the 4.6L modular engine. It is fully OBD-II, and I've made a 'few' changes including the t-stat. You are correct about the computer doing what it can to get the engine up to temp. When I installed the 180* t-stat, I also re-flashed the computer with a new program that told it to accept the lower operating temp, and by doing so was able to adjust the spark curve for more power. Of course I do have to run 92+ octane in her, but hey....
I don't see why the same couldn't be done for a 4banger, but from what I've read, these engines like to run nice-n-hot to keep emmisions down, and efficiency up.
Reprogramming an ECU requires changing several parameters, all of which inter-relate in some way, which means either a lot of trial and error(hopefully with a dyno) or a sound knowledge of the engine systems.
If you try anything, keep us posted. I, for one, am definitely interested.

Peter M