Actually, i'm pretty sure the Stuka has different temp limits per altitude band due to an unpressurized or "not pressurized enough" system (limits are stated in the game's manual).

There are also some tick marks on the 110's water temp gauges if you zoom close enough, they specify the max allowable temp for a variety of altitudes. ;)

That's why I'm confused by the bf 109's cooling chart in the Messerschmitt manual for the Emil. These are the temperature limits for coolant at altitude:

http://109lair.hobbyvista.com/techre...als/bf109e.pdf

0 km -> 100 C
2 km -> 95 C
4 km -> 91 C
6 km -> 87 C
8 km -> 82 C
10 km -> 78 C

It's similar to water's boiling point at altitude but about 10 degrees off. So it almost appears to be subjected to atmospheric pressure changes. However, as mentioned before in this thread, to be contained in the system it would need to be sealed, and thus pressurised, otherwise it would leak (especially in a fighter that can be found at different attitudes e.g. upside down). So there must be another reason for these temperature limits?

The manual also states that the coolant is merely water with some rust inhibitors and that 30% glysantin/glycol is only added when temperatures are around freezing.

The schematics for the cooling system show bleed valves for over pressure. The circulation pump seems to be part of the engine or there is a convection process that circulates the coolant?

Is it something to do with that air doesn't transfer heat as efficiently at altitude because it is less dense? However in that case the temperatures limits shouldn't need to change you would just have to open the radiator more.

Or are they precautionary limits as it takes longer to cool at lower air densities? However, I'd imagine the colder air would make up for this? I don't know I work in IT this is all beyond me.

My idea about the lowered allowed temps at alt. is simple that the thinner air can't transport enough thermal energy.

So, as the outlet-temperature of the radiators is the important value here (it is known how much thermal energy will be produced)
the pilot must control the indicated inlet temperature to a point where the radiator is able to cool the coolant to the needed max. outlet-temp.

Just an observation with the 109 coolant system. When taking a hit I've noticed the coolant escaping and when finally all coolant being evacuated, the water temp gauge would show it completely off the right side(as high as it could be).

In my observations of real life coolant failures (in automobiles however) this is the exact opposition. The gauge should be showing the minimum temperature.

That depends where the sensor is mounted, at the engine -> heating up without cooling, or in the coolant circuit -> cooling down without fluid to transfer the heat.