Originally Posted by B Eventually
How does one know the line between hot and too hot?
That is a good question and a bit tough to really know as engines tend to have different tolerance levels for getting hot, both from a one or two time event and chronically. In general, aluminum block and head engines are less tolerant to overheating than aluminum head on cast iron block (what Chevy does on the heavy truck gas engines like a 3500 van) or cast iron for both heads and block. The Promaster appears to be an all aluminum engine design.
I am very conservative on what I want in maximum temps, so keep that in mind. We have an 07 Chevy 6.0 cast iron block with aluminum heads. It also has a different thermostat position than most of us remember from other engines although I think it works close to same for most part for temps seen.
The thing that I have found with essentially all engines are that there are visible steps to the temp climb in most engines and you can spot them quite easily if you have a good gauge that you can see digital temps or a very wide scale analog.
Normal will be that the engine is operated at what the thermostat is generally rated at, or close to, and steady. In this example choose about 193* which is typical in our van.
Step one is when the engine sees more load or worse cooling for some reason, like going up a hill or mountain or having a huge tailwind to reduce radiator airflow, even being behind a truck can make temp climb if you are marginal and this happens often in the mountains. At this point the thermostat is still trying to control temp by opening more, and to open more thermostats need to be hotter and hotter. The temp will slowly climb as the thermostat opens until the thermostat is wide open. We see this until we get to about 210* in ours. At that point the thermostat is wide open, so the temp control falls nearly completely the radiator. In most cases the radiator won't quite be maxed out at this point so it is likely that the temp will level off or start climbing more slowly.
Step two continues on with heat up until the radiator is maxed out and can't keep up by absorbing the heat into it's thermal mass reserve and has to rely on only the cooling air for keeping cool. On ours this point is not much higher than the 210*, usually under 215*. Once everything is that hot and all you have is the same amount of air, if you are still generating the excess heat that got you there all is lost for control and it can get very hot, very quickly, from there. Once that happens you can get to the point of generating internal steam in the engine and that can give extreme hot spots around the heads, potentially warping them or damaging head gaskets. If we get to more than 220* for more then about a minute (temp sensor location makes it so you can see quick blips on ours sometimes like if behind a truck blocking air) we know it is time to do something to reduce the load or stop and let it cool off.
Most of the newer vehicles will either light a hot lamp or reduce power at some level, but it is often hotter than I like at maybe 240+ degrees.
If you get to the point of knowing how the temp pattern works, it allows you to address the issues before it gets to the rapid end heating climb, so you have enough time to find a place to pull over or get to a slower lane, etc.
A different discussion is how to address the extra heat being generated if it is found to be an issue. On our 4 speed auto Chevy, we found the torque converter lockup programming to be a huge contributor in generating heat that got put right into the radiator by the trans cooler.