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Confirmed with a scan-gauge, my 2000 Civic runs about 195*F (which is how it should be) when the temperature **** is set to full cold. When I turn it to full hot, even with the fan off and recirculating the air, the coolant settles to about 177*F. I'm concerned that running this cold is affecting my mileage and will cause a tad more engine wear.

The thermostat was replaced about a year ago during a timing belt change. I know that when the temp **** is set to 'heat,' a valve opens allowing coolant to circulate through the heater core, but why does it make such a difference? Has anybody else noticed this issue?

 
Rep Power: 518

Sounds average to me.
177 is well within reason.


SPECS:
Start to open 169-176
Fully open 194

Cooling fan ON 196-203
Cooling fan OFF 5-15 below actual ON temp

 
Rep Power: 204

I had to do some work to my cooling system last fall and thought things seemed not right but everything has been totally fine. My coolant reaches about 176f and regulates to that temp.

Some screenshots from my OBD II reader

 
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I appreciate the responses guys, that's very helpful. Temps in the 170s does seem strangely low to me, as from what I recall of old automotive textbooks, the peak efficiency and minimum wear occurs right around 195*F.

I seem to remember something about engine wear at 180*F is about double the engine wear at 195* or something to that effect.

 
Rep Power: 518

Yeah maybe.....but these cars are designed to be like this, and can go forever like this.
(Had a 98 or 99 Civic in the shop last week getting all the brake and fuel lines under the car.....397,xxx miles on it and rusting all to hell.)

Plenty of cars (manufacturers) only run 180 stats, even now in 2014..... and I'm still used to GM products that run 195 thermostats and didn't run the fan until 223 or higher. They could actually drop a couple MPGs with a 180 stat.


I'd personally prefer a higher stat rating in the cars too..... Might help heater complaints on days when it's below zero.