I bought my truck/Rodeo back in 98, when it was 5 years old. At the time it had 99K. It now has 171K miles on it, and i'm having problems with it. Within the past year, I have replaced the catalytic converter due to failed emissions, and just last week replaced the thermostat. This is the second time in 8 years that I have replaced the thermostat. When the truck is sitting in park while running, the temperature gauge starts to rise towards Hot, until I give it gas and get the juices flowing a little bit. My Check Engine light comes on all the time, and the place that fixed my catalytic converter actually cleared that problem for a while. But then it came back. The same place also replaced my radiator, and timing chain at one point about 2 years ago. Can you tell me what might be keeping the thermostat to fail and making my heat guage go to hot every time I idle the truck? Also, is the Check Engine light ONLY associated with an emissions problem?