Changed coolant. Why did the outside temp gauge temporarily disable?

After 8 years and 130,000 miles, I changed the coolant. Not that color is directly related to coolant integrity, but it was pure pink. Even the overflow tank had not the slightest bit of sludge. I changed it anyway.

I changed it properly: drained the block, used a Lisle Funnel for burping.

When I went out for the first drive, the outside temp gauge said 61º, even though it was clearly 80º outside. It stayed that way for about 10 minutes. Then the temp started to go up..... 63º, 67º, etc. until 1 minute later it read the correct 80º.

I did not notice the reading when I was running the motor and burping. The only thing I can think of is that it was probably 61º in the garage when I started in the morning.

What is the relationship between the outside temperature sensor and the cooling system?

 

My '15 Tacoma PreRunner does not have an outside temp gauge.

My wifes '14 4Runner SR5 does and it behaves the same way you described. If it's 45F when she gets home, it will read pretty much the same when I back it out of the garage in the A. M. and the outside temp is now in the 20s. I suppose the correct temp is displayed after the vehicle has been underway for awhile.

 

Did you disconnect the battery? ECU getting its bearings?

 

Has this happened before you did the coolant flush or has it only happened after doing the flush?

 

OP both of those systems have zero in common, you are seeing things.

 

This.

 

I would go with this theory.

 

Seems very strange. I did not disconnect the battery. When I park in the garage and the outside temp is different, it normally starts to catch up as soon as I "round the corner." This time it wasn't until I was well underway on the freeway, it it was a 20º differential.

 

Probably spilled water or coolant on the sensor, it needs to dry out to read properly. This happens to my truck every time I take it to the car wash.

 

The temp gauge is not instantaneous.

It was 39 in my garage this morning. Took several minutes to read the true 19 degrees it was outside.

 

My truck is garaged all the time, not heated. There is always 10 - 15 deg difference between garage temp and outside temp. After a little while of driving, the temp is correct.