Quote:
Originally Posted by mikefocke
So both are right under different scenarios?
Reading you both...
The low-temp isn't going to let more coolant through to the radiator (just sooner) but in the low speed running low thermal-loaded state the temps will be lower thus when the engine needs more cooling the radiator coolant starts out from a lower base.
Raise the temps toward or to the thermal max of the radiator (as in racing or A/C on on a hot day) and the low-temp thermostat will have no effect as the same coolant flow will get to the radiator and the radiator will cool to its max (if the leaves have been cleaned out).
It will take a while for the coolant to return to lower temps (because that only happens when the radiator can remove more heat than the engine is producing) even at low thermal-load road speeds but the low-temp thermostat will allow eventual return to a lower state.
On a road car, the oil will last longer because it spends more time at a lower temp.
So I'm left with the questions:
What is the real coolant temp difference between running at a constant 40-50 MPH and 70?
Once you raise the temps to the max the radiator can handle, how long at a moderate speed does it take for the temps to drop to the point where the low-temp thermostat makes a difference?
How much does the ambient temp influence the max cooling capacity of the radiator? IOW, how hot does it have to be out on a road car (because most of ours are) before the low-temp makes no difference after warm-up?
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Mike, the difference between 40-50 and 70MPH is not substantial in terms of the "steady state temperature of the coolant, but the rate of change (how quickly the car will cool from the heavy traffic temps) when coming out of traffic onto an open road is higher for the car going 70 due to increased air flow over the radiators.
At an ambient temp range of 68-72F, it will take a few miles for the engine to shed excess heat with either stat, but what does happen is that as you approach the nominal "steady state" temp of either stat, the thermostat begins to throttle the coolant flow a bit, so the rate of change gradually slows and begins to cycle up and down slightly until is settles at the nominal steady state temp. Because the available heat transfer rate is basically constant (limited by the radiators and air flow), the OEM stat will reach its steady state temp sooner than the 160F stat will as it does not have to shed as much heat.
Ambient temps do have a significant impact on cool off rates; a car running in 40F air will cool much quicker than one in 80F air. But in either case, again at steady state, the car with the 160F stat will be running much cooler than the OEM stat; the only thing that really changes is the delta or rate of temperature change attributable to the difference in air temps.