Quote:
Originally Posted by shadrach74
JFP,
Thank you for the explanation.
Have you instrumented the "steady state" temps you're speaking of?
Your explanation contradicts my understanding of the principles of thermo dynamics. If the car runs steady state of 210-215f with with a 186df thermostat it should run the same with 160df thermostat. Both thermostats will be wide open flowing fully. The engine produces the same amount of heat and the cooling system has the same capacity. "Turning the cooling system on sooner" should have no effect on the steady state operating temp.
As to the "once and for all" comment. I'm not talking about water temp,in the radiators, I'm talking about the block. As far as heat in the cabin, I was not aware that the thermostat controlled the flow to the heater core, that is uncommon in most cars. What i am concerned about what is important to engine longevity for cars operating in a 4 season environment, the oil temp. Adding 30df radiator coolant to an engine that has just gotten its recirculating engine coolant 160df is a recipe to slow the warm up to steady state temps... Like adding ice cubes to a pot of water that your trying to boil.
My contention all along has been that the only thing a low temp thermostat does is slow the time it takes for the engine to get to "steady state" and you've not changed my mind.
Those of you running low temp thermos: What changes are you seeing on your temperature readouts? Notoriously inaccurate or not, the gauge ought to at least be consistent in its inaccuracy (I mean there not made by Smiths or Lucas) and show a lower steady state operating temp if what JFP says is the case...even if the number is wrong.
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Yes, we have seen this both on cars with full instrumentation (after market coolant and oil temp gauges), but have also seen it using PID scanners as well.
The steady state I refer to is the equilibrium temperature the car settles at when running at a steady highway speed (50-60MPH) on an average day (say 68-75F air temp). I think that you are overlooking the heat transfer capacity of the cooling system in these cars, and the throttling effect of the stats; stuck in traffic, a car with a 160 stat will eventually get warm and kick the fans on, but it takes longer than with the 186 stat. Once either car gets moving, both will settle back to a steady state condition, with the 160 stat car settling at a lower temp (usually around 175F or so). This is the impact of the heat transfer capacity of the cooling system. But the car with the 186 stat settles at a much higher temp, often north of 210F. If you put both a 160 stat and an 186 stat in a beaker of heated water as I mention earlier, you would note that at around 170F the 160 stat is wide open, while the 186 stat is still closed. As the water gets hotter, eventually the 186 stat starts to open, but is not fully open until well past 200F, restricting the coolant circulation up to that point; so it is "throttling" the coolant flow. So even though the car has the capacity to transfer the heat out of the engine at steady state, the throttling of the 186 stat restricts the coolant flow and keeps the coolant hotter at the same speeds and air temps.
The inaccuracy of the dash display is actually two fold; it is inaccurate across much of its "band width", but it is also non linear (it does not "sweep" equal amounts for an equal amount of coolant temperature change). On a car showing 180 degrees on the dash, it is not unusual for a PID scanner to read 210F, yet both the scanner and the dash are getting their information from the same sensor in the engine. In essence, the temp display is little more than a "not over heating/over heating" idiot light replacement.