So I recently changed out my thermostat and now my temp gauge while driving goes from 180-200 and back. any ideas what i should look at? I have ran it about 200 miles, keep checking for air in the system but havent found any yet...

Help!

 

I put new thermostat in my 95 Chevy S10 Blazer and it do the same thing and my other friend have 97 Chevy Blazer do the same thing too. So it might be normal or not I don't know. My temperature gauge didn't work until I put new one in.

 

usually what happens is the thermostat opens at the "peak temp" causing the drop when the coolant starts to circulate.
i have an aftermarket gauge in my ride and i can see it hit 200 then drop to 190 when the t-stat opens up, does it all day long....i am thinking what you are seeing is normal....just based on my exp.

 

This can be a sign of a somewhat sticky t-stat. Thermostat's shouldn't 'snap' open or shut, but regulate between the two extremes. If the stem is a bit sticky, it can cause it to 'snap' in one or both directions which can cause the temperature to fluctuate like you are experiencing.

What brand of t-stat did you install? I have never had this problem with a Stant Superstat thermostat. AC Delco t-stats are good from my experience as well.

It really isn't a problem so long as you have already ensured that there isn't any air in the system. If it really bothers you, swapping out the t-stat will likely correct it.

As a test, before installing the new t-stat, but after you've removed the one that's in there, toss them both into a pot of water. With a cooking thermometer, watch the temperature. The t-stat should start to open somewhere around 180-185*F (stock 195*F t-stat) and be fully open by 195*F. Water boils at 212*F.

 

I am running a Failsafe thermostat on my and I just talked to a guy at AutoZone and his 96 Blazer do the same thing so he told me that it just normal.

 

it is a brand new stant 195. replaced my old one that held steady while driving because it was acting like it was sticking, on first start up I would watch my temp gauge spike at 220 then drop to 180 and hold there steady...

 

I usually don't go for the regular Stant, but the Stant Superstat (#45119 for the 2nd gens). Nearly twice as expensive, but still a bargain at ~$7.

 

I have Failsafe in the last 3 vehicle I had and I had no problems with Failsafe thermostat.

 

well, looks like Ill be grabbing another stat this weekend and trying that, otherwise Ill just leave it alone and let it bounce....