Combustion temperatures on 2 stroke and 4 stroke gas engines and diesel engines in the combustion chamber are well above 1200'F depending on load conditions. It is not uncommon to see the exhaust next to the head glow various shades of red especially at night or low light conditions. I looked up a color chart for different types of iron and this glow will start to happen at about 1000'F and keep getting lighter and brighter as the temperature goes up.
The Defender does not appear to have an EGT sensor so the engine temperature will be controlled by the ECM, the injectors, engine knock sesor, air temperature and cooling system. The ECM is programmed on the rich side to help keep exhaust temperatures in check especially at WOT.
The two stroke engines have always had a temperature concern they always ran the best just before they seized. During the carb days some of us ran Exhaust probes especially if we were running an aftermarket pipe. The Skidoo engines would not tolerate temperatures above 1200 F for more than a second or two before you burned a hole in the piston.
If you are concerned about the exhaust temperature near the engine starting a fire you shouldn't be as manufacturers typically install an aluminum heat shied to protect anything that could be flammable. On the other hand if you are driving around in deep grass, hay, or other flammable things that might accumulate on top of the engine it would be a good idea to blow that area clean after a ride with an air hose. You can get stick on foil backed insulation to put on the underside of the cab near the hot spot of concern or you can get header wrap insulation that you can wrap the pipe next to head to keep the temperature inside the exhaust system. I have not used either.
Wow! We have tracks on our machine and at 3500 ft, we run at 5500 rpm for hours... high range, across the frozen lakes.
I will have to watch out for this!
Catching fire is unusual, have you been able to find the source? If the machine is stored out in the open it may have been a rodent storing food or building a nest?
If you are able to find the source give us an update.