LPG is indeed a hot set-up, this is the reason why you need some sort of protective oil that goes with your fuel feed... otherwise, the spark plugs will foul faster and engine wear will also be accelerated. If you want to do an LPG conversion, you need to go to those who have shops with good reputation.

Another thing is, when you go lean burn, it's like using LPG... both ways will heat up your engine temperature. This is why it is not recommended to run with a lean setting.

Unless you have supplementary fuel that will aid the combustion speed from the flame front near the power stroke of the piston. Increasing the flame speed will keep the hot gas or combustion out of the cylinders before the valves closes totally. The reason why it builds up heat is because the fuel mixture is too dry, the standard 14:1 mixture of Air and fuel is just enough to do some cooling effect to the chambers.

The gaskets are good for at least 200 deg. Centigrate or more... but if heat is building up from the cylinders... the engine temp will rise to above 95 deg. most of the time... causing gaskets or seals to deform or crack. Silicon gaskets may withstand about 200 deg. C. neoprene - maybe a bit more. Engine temps.. near the exhaust side can go much higher.

If you keep the mixture at standard setting with normal fuel, you can keep the temp lower.