Engine runs on the cool side?

[Crowder1980]

I guess at stop lights the engine doesn't need much cooling because that's where the needle starts noticeably dropping, bad thermostat makes sense., Just out of curiosity would a stuck open thermostat have any effect in 90F ambient temperature?

 

[The_Nuke]

pull the tstat and drop it in a pan of water on the stove. stick a thermometer in there and turn up the heat. make note of when it starts to open and when it gets fully open. they should not be very far apart, and the open temp should be whatever the tsta is rated for.

 

[SatinSilver]

17 year old car with almost 200k miles, time to change the t-stat with an oem one. Shop Amazon for best price most likely.

 

[Driz]

Does it have a tiny burp valve on the stat housing. If so open it running until the fluid runs bubble free. My old Hondas acted like that when they got a tad low on coolant. It ran slightly cold The the needle would gently bob from slightly low to slightly high when it warmed up and started to get hot. Something about the top of the radiator being below the engine head causing bleeding difficulties after opening up the cooling system. It may not apply to your car but the symptoms are similar.