Much ado about thermostats
Jim and all, I'm not a thermal engineer, but I think many are attributing too much credit to the lower temperature thermostats to lowering the running temperature of our "Rods". Just humor me for a minute or two here... I'm not sure just what the percent of total coolent resides in the radiator and hoses versus what is actually in the channels that run through the engine block to cool it, but my guess is that it is at least 60% of the coolent is outside the engine block and associated hoses that are closest to the heat source, the combustion chambers, heads, etc. Anyway, no matter what temperature rated thermostat you have, they are all closed until the heat generated by the internal combustion, friction etc, heat the coolent that resides in the engine block etc to let's say 180 degrees, and assuming that you have a 180 degree thermostat, shortly after the coolent temperature gets to 180 degrees, the thermal reactant metal opens the thermostat and allows the water to flow freely throughout the cooling system, radiator, block, hoses, heater, etc. Now, when the hot coolent that just opened the thermostat mixes with the much cooler liquid in the radiator etc, the thermostat probably will close somewhat and restricts water flow... it can't help it.. but over time, the full amount of coolent is heated to at least 180 degrees... it may take a little longer for this to happen than if you had a 160 degree thermostat, but let's just say for arguement sake that once all the coolent is heated to at least 180 degrees, the thermostat is now wide open and the coolent continues to increase in heat as it is circulated through the engine block and heads. Since there is no variation of the temperature of the combustion and friction, the coolent will eventually reach a consistent higher temperature to dissipate the heat from the block and heads. The thermostat now has no effect on coolent temperature what so ever... now the radiator must do it's job of dissipating the heat through it's cooling coils, and we all know that when the beast is idling, not moving, and the fan is not moving any air through the coils to dissipate the heat, the coolent will continue to heat up and eventually, will overheat the engine and all. For cars with a manual fan that is belt driven, we also know that so long as the engine is running, air is being forced through the radiator coils at some rate, and this is what dissipates the heat from the coolent and keeps it from overheating. In our beast this is accomplished by a rather complex monitoring system that takes temperature input from sensors and then determines how fast the fan must run to compensate for the lack of air moving through the radiator coils to sufficiently cool the coolent and that also takes into consideration the speed of the beast, whether additional cooling is needed because the AC is running, and of course also how fast the engine is running as the higher speeds with more frequent combustion explosions will create more heat that needs to be dissipated, but also causes greater natural air flow through the radiator coils. So now, the total cooling system with PCM monitoring and commanding the fan to work faster or slower is all calculated so that the engine coolent remains at an acceptable temperature... and that seems to be somewhere between 190 and 235 degrees. After all this, I don't see what the rating of the thermostat has to do with any of this except that the lower temp thermostats will start the full flow of coolent throughout the cooling system earlier, but after a relatively short time with the very high combustion temperatures and friction heating the block and heads, the coolent temperature soon will get to 190-235 degrees no matter what. It seems that the only thing that keeps the coolent temp around 190-210 degrees is the PCM commands to the fan, controling the speed of the fan, thus the amount of air passing through the radiator coils. Some of us have experienced the fact that driving greater than 40-45 mph forces enough air through the coils to keep the coolent within it's tolerable range. So bottom line, the thermostat has little to do with the running temperature of our beast... it is all dependent upon the fan to supplement the air flowing through the coils as obviously, there is too much free air flow restriction from the grill, the nice looking black honeycomb mesh, and all the other stuff that is blocking free air flow through the radiator to keep the coolent within range through the normal stop and go driving conditions we all experience when not on the open road. Once the coolent reaches this higher operating temperature, all the other complex combinations of sensors and PCM interaction should keep the beast running rather well. All we need is a fan that does not fail. And I would say that in most cases... the cooling system is working very well... for some reason, there are an overall statistically few number of cases where the fan fails and we have trouble. It would be interesting to know just what percentage of the total vehicles to date have had cooling fan defects. Based on this forum, I would guess that there are maybe 50-75 reports here (and I think that is greatly aggressive) out of about 22K vehicles... that is about .3% failure rate. Maybe that is why we have not seen any corrective or remedial action taken by GM. One thing it has done for sure, is it has created some great and lively exchanges and I've enjoyed all of them... Just my $.02 worth here. :cool