Most likely. If you all the way up to the high mark and let it sit there you have probbably done some damage. Get a compression and hydrocarbon test, and read the Overheating thread on the main page.redtegrs91 said:sorry for hijacking the thread but i am having the exact same problem. my car just overheated and it went all the way upto the H mark for about 10 seconds. Did i damage something? I shut it off and let it cool down a bit then drove it again. the temp was fine as long as i was driving.