I thought the only thermostat in the system was the one that opens to allow coolant to flow thru the engine. The only reason there is a thermostat to begin with is to restrict flow to let the engine get up to running temperature faster. As soon as you hit the thermostat trigger temp, it opens to let coolant flow. I assume after this point, the thermostat never closes again as long as the car is running because the coolant stays above the trigger temp, sometimes far above the trigger temp (30-40 deg C?).

One could assume the temp at which the thermostat opens is near the "ideal" running temp and the radiator would be sized to maintain the coolant at or near this temp. In keeping with most mass production items, there are probably compromises with weight and cost of the radiator which limit it's ability to maintain this "ideal" coolant temp under extreme conditions (severe driving, really hot weather, etc.). This is where the ECU comes in; when it sees the coolant temp rise (in conjunction with air temp?) it does it's thing to protect the engine, but driveability suffers.

One thing I wonder about is which factor does the ECU take into account more: the intake air temp or the coolant temp? If the system gives much more weight to the air temp reading, even if we significantly change the coolant temp it may not impact what the ECU does.

Doesn't Mugen usually have engineering data to back up their products and claims? I was going to call Scott at king motorsports and talk to him about the mugen radiator - maybe he can send me temp data.

 

spoon has a radiator as well i believe

 

A thermostat will open and close in response to water temperature. The stock unit is closed below 169F and fully open at 194F. Depending upon the heat generated by the engine and the cooling capacity (radiator/ambient temperature/air flow) the thermostat will cycle as needed. It will only stay fully open if the radiator is incapable of getting the coolant below 194F. A big radiator cooled by a good flow of air could reduce the water temp so the thermostat closes more often.. buys nothing in performance over a smaller radiator that is doing the job.

 

a replacement radiator could possibly be lighter weight and could have better heat transfer depending on the material.

 

A bigger/better radiator would be way down my list for a non-tracked or lightly tracked car.

 

By the way, with the Mugen radiator cap and thermostat and the Spoon thermoswitch, I often see the dash temperature reading go back down to two bars after it's been at three if I use the heater in cool weather with light engine loads.

Without good water and oil temperature gagues, this doesn't mean much, but maybe something...

Ted

 

Does this affect VTEC engagement limiter?

 

I think I can still VTEC with two bars (after it's been to three), but I try not to wind it all the way out until it's been at three bars for a while. I also usually turn the heat off to get the gauge back up to three bars when this happens.

 

I also see this happen (dropping to 2 bars under light loads) infrequently. Usually, it is cruising at high speeds in cool weather. In my case, all I have to do is hit the gas and the 3rd bar lights back up, indicating that I am running right at the edge of 2-3 bars.

For my last long drive, I re-installed my grill cover. This kept the temperature at 3 bars consistently, even in 40-50 degree weather.

Tanq