How do you know if your thermostat has gone bad? ie there is hot air coming out of my vents when the setting is on cold, but the temp reads normal, but the air coming is out is kind of hot. Thanks.

 

your engine's not overheating= your thermostat is working

 

Bad thermo wouldnt blow hot air. Bad Thermo can sometimes lower temps when your switch to heat and full blower on(Means its stuck open believe). Sounds like something else to me

 

What could cause the air to become hotter?

 

No, your thermostat is fine. Some people don't realize that a thermostat controls the MINIMUM temperture your engine... not the max. To prevent overheating the ECM or a thermo switch will turn on the cooling fan as needed. The cause for hot air could be anything from a stuck open hot water valve (located in the heater hose under the hood, with a cable going to it) or a broken blend door in the HVAC box, or maybe your AC doesn't work and it just seems hot.

 

i have no ac