hello, I just purchased a 99 grand prix SE about 2 months ago, has a 3.1, 240,000 miles on it. Seems to run great but it got down to -20 degrees about two weeks ago and the car started to overheat driving to work, so i pulled over, shut it off, waited 15 mins and restarted and it was cool and stayed cool. ran fine coming home and ever since, dont seem to be losing any antifreeze and just changed oil sunday and found no water in the oil. the antifreeze however is very dark brown, could barely tell the rating which was -22 degrees so im thinking the coolant froze, engine got hot, and coolant thawed and started to circulate. the car has not got hot since that incident however my main question is the car has had a random misfire that comes and go since it got hot, never once did it before it got hot on cylinder number 6 (the back one) so its damn near impossible to thread my compression gauge hose into. Thinking it could be a head gasket or intake but like i say theres no water in the oil, and i dont seem to be losing antifreeze. also heat stays hot and car does not go above thermostat temp. (190ish) any ideas? i dont want to throw alot of money into it if its an intake or head, only 600 into it. Could also be a spark plug or coil or wire but think its weird it started doing it after over heating.
