Quote Originally Posted by LivesNearCostco View Post
My car is a 2003 (August 2003 build) and if we believe the indie shop that once serviced my car two owners ago, my thermostat has 85,000 miles on it and was changed around 2008. I did put in a new aluminum bodied one 10 months ago but it stuck shut, throwing a code and overheating my car, so I put the old one back on.

This morning I drove the ZHP to work (instead of the beater car) and conveniently got stuck in street traffic. Air temps 45-48F. OBC coolant temps cycled same as yesterday... rose to high 70's while driving, 80's at stoplights. When I got stuck in slow traffic, it cycled as follows
88 to 90 to 88 to 90 to 88 to 91 to 88 to 92 to 88 to 91 to 88 to 92.
On the freeway it went back down to the high 70's, and when coasting down a long off-ramp with zero throttle went as low as 73C. When parking got back into the high 80's.

Maybe my thermostat is stuck open. I have a new Wahler thermostat leftover from the warranty replacement of the aluminum one. Maybe I should put that in.

When my coolant temp cycles between 88C and 92C does anyone know if that is the thermostat opening and closing or the fan turning on and off? Are these thermostats set to open at 90C? 95C?
Just a guess on my part but I would think it is the fan kicking in at 92. Since mine seems to run at 205F I would think we have a 95C stat. I heard my fan kick in while I was idling the other day but my temp was at 210F iirc. Not sure why yours is kicking it at 92. Faulty temp sensor?