to the shop 3 times and it would never overheat while they had it. Last month I said to let it run for 4 hours with a/c on and it it still would not overheat for them. This week it goes to full hot and I turn on the heater full blast pull over car and both fans are running and the overflow is boilng and smoke is coming off overflow. I stll am not loosing water, hoses are fine , just changed the oil before this week and the old oil was fine,.Could they have put on the wrond temp. thermostat and radiator cap. Why does it do this and all fans are working. Turning on heater use to fix it but something is not allowing water to flow to cool off. Now I am afraid to drive it to shop 6 miles away. It could crack the head. It is even 60 degrees outside and that should help if i keep it moving with heater on full blast. Anyone have any ideas? I think the shop owes me a free service because it never stopped but it is a mystery and I went to shop and even days later it would never heat up Random, but now dangerous.