Engine temperature behavior

[Racincc85]

I've got a 99 nissan altima with 116k. I recently replaced the thermostat and flushed the cooling system. It is extremely cold here in the western suburbs of chicago tonight. I was out driving my car about an hour ago. I went from my friend's house to the gas station. My car had warmed up to normal operating temperature which is about halfway up the temperature gauge. After I filled up I started the drive home. I was getting colder so I turned the heater on full blast. When I did this my temperature gauge dropped from the normal halfway up the scale to only a quarter way up the scale. This seemed kind of strange so I turned the heater back down and it went back up to its normal position on the scale. Is this normal (it is my first car that has a temperature gauge so I have never have seen this before), and could the engine have been harmed by this sudden cool down and warm up? Thanks!

[curtis73]

No harm done. Keep an eye on it. It may be perfectly normal, a sticking thermostat, or a failing temperature sender for the gauge. If it overheats or doesn't get up to temp, post the symptoms and we'll troubleshoot from there, but a short trip (less than 10-15 minutes) might not be an accurate test since it doesn't get fully up to temperature.

[mazdatech177]

its prolly just normal, by turning the heater on you are removing more heat from the coolant system via the heater core. this can be a handy thing to know if your car ever starts to overheat

[Racincc85]

thanks for the replies. I'm going to be driving a lot tonight so i'll post back if anything strange happens