Originally Posted By: djb
There is an oil-related point you are missing.
A 160F thermostat is pointless in 115F weather. Under load the coolant temperature will increase well above that temperature, until there is a high enough temperature differential between the radiator and coolant air.
Will it? If the ambient air temperature is 115 and the coolant coming out the thermostat is 160F, that's a 45-degree F temperature differential. Your skin is 98.6 degrees F... go stick your hand under a hot water faucet running at 143.6 degrees F and tell me if there's heat transfer across that 45-degree differential. Or since we're talking about transfer to air, tell me if you're comfortable sitting in a room that is 53.6F wearing nothing but shorts. In practical terms, 45 degrees is still a pretty healthy temperature differential
For *most* modern vehicles, a 45-degree heat source (radiator) to heat sink (ambient air) temperature differential is enough to transfer away all the heat energy lost from the combustion chamber to the cooling system. Heck, its enough in my grossly inefficient 1966 big-block engine with a mere 22" wide radiator.
Originally Posted By: djb
When the load is reduced, such as going slightly downhill or coming to a stop, the engine will quickly cool down to 160F.
The result will be many thermal cycles, not quite as severe as cold starts, but still putting high wear on tight clearance parts.
I think you're making a mountain out of a molehill. There are already parts inside the engine (for example, the center of the piston crown extending down through the wrist pin) that see MUCH larger temperature swings between idle and full throttle all the time. Exhaust valve heads go from literally glowing (~1000+ degrees F) under load to a few hundred degrees at idle, every time you go from accelerating to idling. Yes, there will always be temperature micro-cycles during normal operation. But I personally don't think any engine is going to suffer noticeably from them- the engineers that built them know what goes on and account for it.
And let's get back to the point: we're trying to reduce detonation in a heavily loaded engine. You can do nothing and let detonation pound the bearings to butter, or you can subject parts to a small percentage increase in temperature cycling while alleviating the detonation. Which one OVERALL is better for engine longevity?
Originally Posted By: djb
I guessing someone is going to leap in with "get a bigger radiator to keep the temp at 160F". It won't work. The temperature differential has to be high enough to transfer the heat.
Well... it may not be PRACTICAL for every application, but its not that it absolutely won't work. The rate of heat energy transfer is proportional to both the size of the radiator AND the temperature differential. Increasing either one will increase rate of heat flow. Increasing the cooling air flow rate will also help. You can at least partially offset a lower temperature differential with more area and/or more air flow. IMO, most stock cooling systems have enough reserve capacity to do this under some surprisingly extreme ambient temps.
But my contention is that its not even necessary. Very few cars get out of the factory anymore without passing through the desert proving grounds and passing the tests.
