So today I was on my way home from work when I hit the usual Stamford rush hour traffic. All was going well until suddenly my check engine light pops on. I had a long day and didn't want to be bothered with it at the moment and figured I'd just deal with the situation later tonight. Well 5 minutes later I get a message something like this, "Coolant Temperature something something" and I look at the gauges and holy crap it's approaching 250 degrees! I immediately pull over, shut the car off, and pop the hood. After narrowing it down to the fan or the t-stat I sat back in my car yelling aimlessly. Once the temp dropped down to roughly 170 degrees I decided to play with fire and attempt to give it one last shot before having it towed. Traffic started clearing up, but was still going only 10mph and could see the temp jumping in 2 degree intervals so I decided it was best to call it quits. Since there was no shoulder, and traffic cleared by then I gunned it in hopes of reaching the shoulder but to my surprise the temp began to drop and stabilize. I'm going to hope it's just a fuse or relay, but any other ideas? All help is greatly appreciated.

 

so pretty much at idle/under 10mph the coolant temp skyrockets, but when moving at speeds 20mph+ the temp sits at around 192.

 

My 03 does the same thing. Sittun still it gets hot and about 10 mph is drops down pretty quick. It never gets much over 222 degrees. I have the software on my laptop and went in and reset the fans to come on 5 degree sooner than normal. This seems to have helped a lot. Evidently these motors need airflow plus the pull fans to keep it cool in traffic. On the road my temp stays at 187 (moving) winter or summer.

 

On C5's and newer there is an opening under front near spoiler. Trash acumulates in there leafs, plastic bags etc. cutting off air flow to radiator. Clean out the mess, and install aftermarket screening over opening.