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Old 10-03-2012, 09:15 PM
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Originally Posted by 1965tripleblack View Post
ASSUMING that the cooling system has the heat rejection capacity to pull the coolant temp down to 160 degrees or less, what would be the advantages/disadvantages of a 160 versus a 180 thermostat?
Thanks in advance.
There is a bit of a narrow band where wear is minimized and efficiency maximized that runs about 180 to 210 degrees. 160 gets to be too cold to drive the oil temp up hot enough to get the water out of it. Water comes mostly with the blow-by as the combustion of the fuel and air converts by weight about half the two input products to water and in a perfect world the other half would be CO2. Additionally, as the engine temp falls the mixture has a harder time burning because the fuel remains in globules too large to combust, so some of this finds its way into the ring pack wiping the cylinder lube out which increases the wear rate. The two ways around this without manifold heat from the exhaust is running at a high enough RPM to where the turbulence in the ports physically breaks up the globules, or going to high pressure port fuel injection where the spray impact upon the back of the valve does that job of misting the liquid fuel into something that burns.

210 is popular with the OEMs because it really raises the efficiency of the engine and EFI does a lot to get them around the issues of the fuel losing octane rating as the engine gets hotter because they are injecting cold fuel onto the hot valve were it sits for a microsecond before going in to there isn't time for the chemical degradation to happen to the fuel as with a carburetor or throttle body injection before it gets to the valve. But 210 is also very edgy as far as the complete cooling system goes, one small thing goes wrong in the cooling system and the engine can be par-boiled before you can shut it off.

So running at 180-190 is a safer bet it gives a little space for cooling problems to be caught before disaster occurs and it gets the oil up into that magic range of 190-210 where it cooks the water and fuel contamination out of it.

Smokey thought that racing engine ought to be running at about 400 degrees but he couldn’t get there with the materials engines are made of. Way back in the late 1930’s with the war on the horizon the military was looking for a way to get more power from aircraft engines without having to make them bigger. So as part of the Hyper-engine program many attempts were made to get coolant temps up to around 300 degrees. But again the materials (even those used then were far superior to anything used by even today’s auto engines) just wouldn’t support those temps. Eythlene Glycol coolant was one part of that program which did filter to the automobile in the 1950’s as was detergent oil and the hydraulic lifter. All these things were products needed to operate at those extreme temperatures that found homes in everyday life. Today with ultra modern precision machining, the OEMs accepting the cost of better materials the much improved lube oils both mineral and synthetic, the lube oil is getting mighty thin and this requires temperature stabilization of the engine. These new ones heat and cool the oil and mix cold radiator coolant with hot return coolant in a proportion that keeps the engine hot (210 or so) and eliminates the temp gradients from cylinder to cylinder, chamber to chamber because the inrushing coolant is the same temp as the outgoing so that one part (like cylinder walls 1 and 2 on the SBC) of the engine where the coolant is coming in isn’t thermally shocked by cold coolant while the combustion chamber above it is being fried by the hot returning coolant.

You’ll find that much of this stuff about more power from cold operating temps is just old wives tails and technically obsolete information from past generations.

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