Originally posted by Hdbngr8:
Not trying to start a flame war here but you are only partially correct in your statement. True Q = kA (Ti-To) which describes the conductivity of the radiator. However the heat removed from the system through the coolant is Q = k * mass flow rate of coolant * temp. change of coolant (Q = km(Ti-To)

The t-stat reduces the mass flow of coolant which increases the temp of the system (the energy into the system remains unchanged; therefore if the mass flow rate decreases the temp differential must increase); this is what keeps the temp up when little heat is added to the system. If you remove the t-stat and compare coolant temps (same ambient conditions, some vehicle speed) of the same vehicle running w/o a t-stat will give you lower temps. The heat into the system is unchanged (comparing with and w/o a t-stat) yet the temps are different. It is just a balancing act between the difference in coolant mass flow rates and the coolant temperature.

Example - While on the highway with my 165F t-stat my coolant temp runs at 165F. The power required to move the car at highway speed (65 MPH) is fairly small (I'm guessing maybe 20-30 Hp). With the t-stat removed I run about 150F on a summer day. However in an application where much higher Hp is used (i.e. more heat into the system), such as on track, my coolant temperature is much greater than 165F (near 200F).



OK, I'll buy most of that, but the thermostats use the same sized opening, therefore the mass flow rates should be the same once they are full open. So you can go right back to your temperature differential in your second eqn. to see the difference in total heat flow.
Also, you have to admit that without a thermostat the mass flow rate will go up since there is no restriction and you get a more efficient flow. This would cool better but would never let the engine stay at a uniform temp; something imperative for good operation of the fuel/emissions system. And still, heat rejection of the radiator will be higher if it is at a higher temp than lower, if all else was equal such as coolant flow rate and airflow rate. It makes little difference in the engine if the coolant is at 160 vs. 180 where combustion temps are 1000 degrees and where a good portion of that heat will flow into the cooling system. However, that 20 degrees does make a difference in heat flow as far as the radiator temp vs. ambient temps is concerned since

Anyway, I don't see how anything I said really contradicted what you are stating other than my terminology, but thanks for correction.

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black