Fluctuating Temperature Honda Civic '10

[Gebo]

I was driving a 2010 Honda Civic and I noticed the Temp Gauge would move from slightly below the middle down 2 bars or so
cooler and then come back to slightly below the middle. Sorta weird. And I'm talking about in just a few minutes. Car had
been driven 30 minutes at that time. It's not mine so I don't drive it everyday. Could the thermostat be going bad and sticking
open?

 

[The Critic]

Monitor the coolant temp using a scan tool, but yes, possibly thermostat going bad.

 

[Gebo]

Critic, if I am paying and installing, would you just replace the thermostat? It's not that big a deal, right?

 

[dumkid]

my car does this too, when i get off the highway and coast the temp gauge will drop slightly. idling the temp gauge will rise slightly above normal and then the clutch fan will start to lock up. this engine runs about 190° normally and has a 180° thermostat.

 

[justalubetech]

Thermostat, there is also a bulletin for this gen about the temp sensor on the bottom of the radiator for this gen civic (dont remember if the 2010s were included) but 99% of the time its the t-stat.

 

[2010Civic]

Thermostats are very easy on these. 20 minutes maybe. I drain a little coolant out of the radiator first so less spills out.

On a 13 year old car even if it doesn't fix the problem it isn't a bad idea. What was the outside temperature when it was doing this?

 

[Gebo]

Thermostats are very easy on these. 20 minutes maybe. I drain a little coolant out of the radiator first so less spills out.

On a 13 year old car even if it doesn't fix the problem it isn't a bad idea. What was the outside temperature when it was doing this?

50 degrees

 

[2010Civic]

Once up to temp the temperature guage should not go down at all at 50F. I've had mine go down 2-3 bars when it's -20F but that's way different than 50F.

 

[Gebo]

I was told by my most wonderful mechanic to check the temp sensor wiring, coolant level and if they are good I should
replace the thermostat. She said if she remembered correctly, the thermostat replacement could be challenging for me. LOL

That doggone thermostat and gasket is $42 at Dealership.