Coolant operating temps in cold weather
 

Just curious if anyone has driven their car in these freezing temperatures. If so, what was the coolant operating temperature relative to the thermostat rating?

I've had my car out in 0 degree weather several times. When it had a properly functioning thermostat, it ran at the thermostat rating +/- 5 degrees. When I had a thermostat that had failed open, it would run around 120-130 degrees in temps as cold as about 20 degrees. I never had the car in colder temps with the failed thermostat. In fact the fact that the car wouldn't come up to temp was the impetus that led me to discover the thermostat had failed.

There have been times in very cold weather that when I ran the heater on high, temps would struggle to make it to the tstat rating and hover around 4 to 5 deg below temp

Most of my cars were at one time daily drivers and endured extreme cold weather. Was pretty common for the engines to run cold well below the thermostat temp, we often had to put some cardboard in front of the radiator to get the engine temp up higher. A couple of my modern cars do the same thing.

I'm running a Mr. Gasket 180 thermostat which I believe allows a small flow through it all the time. I have a four row OEM radiator combined with my 350 block for a total coolant capacity of 22.5 quarts. With ambient temps below 70 degrees, my operating temperature on the highway is about 165, and 155 in town.

Texas summertime temperatures bring the engine temps up to the 180 thermostat rating in the city, but I run 210-220 on the highway when it's 90 plus degrees outside.

Your circumstances are very similar to mine with my 180° thermostat. Just not quite as warm on the highway unless I have the AC on. Though I don’t recall what brand t-stat I have. I’ve tried a couple with the same results. I wonder if I have coolant getting past it in the closed position somehow.

Not cold but cooler weather. If the ambient is in the 60's or lower it will run 170-175 on a 180 thermostat. If I am stuck in stop and go traffic it will climb to 190, courtesy of a small rad. If the ambient is in the 70's or higher it will run at 180. If I'm stuck in bad traffic, I've hit 210. It comes back down once I'm moving decently.

Here in NH with a 160 degree thermostat on a cold day the temp gauge reads right at 160. With the heater on high the temp will drop just below (155?) the 160 degree mark.

I have a pretty beefed up cooling system for my low compression 400, so during the winter months I'll have trouble even coming up to temp here in South Florida if just cruising around town. It'll build more temp on the highway. Because of where I live, I have a 160 degree hi-flow stat.

I've never really understood how to interpret the temp gauge on the 2nd gen T/As. At least the later ones. I've always assumed the first tick on the gauge represented 160, since that's what's between 0 and 220 which is the middle of the gauge. In the summer months, if I don't have AC on, the needle will either be at or just below that first tick, while in the winter months if it's as low as 65 degrees, it'll be two-three needle widths behind that first tick. Even more if I'm running the heater. I know it's not coming up to temp because even after an hour or so of driving in cold weather, I can grip the radiator hose and it just feels luke warm and has barely built up pressure. I can even rest my hand on the valve cover and not get burnt.

I've considered putting in a 180, but the 160 gives me peace of mind for the summer months because they can be brutal down here.