omega b mv6 gets too hot with pendant

Hello driving a 2000 bj omega mv6 let me install a gas system two years ago. now the engine has recently the problem that it gets too hot with trailers when it gets really hot outside so that I have to turn the car off. the fan runs and trozdem goes up so far in the red area. I was already in the factory but could not help me either. can someone give me a tip that had the evt as well.