I was doing a race with 100% damage on. After 5 minutes of driving the engine starts to overheat. I thought that I was driving it to aggressive and tried it again with a very conservative shifting approach (shifting about 1000 revs earlier). But again: After 5 minutes in the engine starts getting too hot. It's pretty frustrating since you can't change the cooling ducts on this car. EDIT: The same thing happens with 75% damage. I really want to racee with higher damage than 50% but thats impossible with this issue.:/
I think you have to reload the session to clear the bug. That worked for me anyway when I had this issue twice.
