Why did we change thermostats for summer/winter?



The brothers took a call today which made reference to an old time practice of changing to hot/cold thermostats for summer/winter.

For the life of me I can’t remember the supposed theory behind why we did this.

Was it just to look busy?



maybe because back in the “OLD” days the radiators weren’t as good as they are now. and probably the whole cooling systems weren’t as good either.


Not everyone changed thermostats with the seasons. This practice, along with blocking the radiator in winter, has, thankfully, gone away.


In the old days, many of us filled the radiator with water in the summertime. At 180 (or 195) degrees, the water is well on its way to boiling. Therefore, we would put in a 160 degree thermostat. In fact, some people ran their vehicles without a thermostat. There also was a non-permanent antifreeze that we used in the winter that had a low boiling point. I think DuPont made this under the name of Zerone (Zerex was the permanent antifreeze). We would drain the non-permanent antifreeze out and put in water for the warmer months.

Also, by switching to a thermostat that opened at a higher temperature, the heater put out warmer air.

I also think that we today’s cars run a higher pressure in the cooling system than the cars of the 1940’s and 1950’s. Therefore, the coolant doesn’t boil at as low a temperature.


Well, I think cars used to have a lot more trouble controlling engine temperature. Not all cars, but cooling system technology -while fundamentally similar- has changed a lot in the last 30 years. Simple radiator design has improved greatly. So if you have a car that overheats in the summer with a 190 degree thermostat, and runs too cool in the winter with a 160 degree thermostat, you have to swap them when the weather starts changing. Modern cars are so good at maintaining a constant engine temperature despite load and ambient temperature, that it’s not necessary on any car.

A lot of the time, older cars have cooling system problems from lack of upkeep and natural rust / scale deposits, etc. People tend to go for the easy fix in those cases and just stick in a lower-temp thermostat. That might help for some situations, but it’s not a solution to overheating and is ultimately a bandaid. Some people go so far as to remove the thermostat altogether, and that can actually make the situation worse.


160 in the summer to limit boil-overs. 180 in the winter to make the heater work better.


I believe one reason for the cooler summer thermostat was to keep the oil cool during the summer months. Oils of that era couldn’t tolerate hot engine temps like today’s oils can.

Another reason for the cooler summer stat was to keep the alcohol-based antifreezes from boiling (and being driven out of the system so quickly).

As far as removing the thermostat altogether, that was popular in the garage I hung out in as a young teenager in Connecticut. However, I was quite surprised to learn from a radiator shop owner in Arizona that removing thermostats in the summer actually made cars tend to overheat even more. He explained presence of the thermostat slowed down the water circulation enough so the water traveling through the radiator would have sufficient time to cool.

On a related note, my grandfather used to add new antifreeze into his 49 Ford every year. The year he got too old to drive (and couldn’t go to the store to buy antifreeze), he took a few gallons of his homemade wine and poured that in the radiator. The engine block cracked that winter.



I don’t know of anyone ever CHANGING the thermostat…But I know a lot of people who use to REMOVE the thermostat during the summer. Run straight water and just keep it circulating.


I’d be surprised if blocking the radiator has gone away in North Dakota. When I lived there I discovered that it was simply impossible for the engine to warm with even a small amount of bypassage past the T-stat unless the radiator was blocked. The only change to cooling systems since those days is a higher T-stat rating to burn cleaner. And electric fans.

Which brings me to the reason we used to chage T-stats. In the days of 165 degree stats, we needed a bit extra heat on some cars to get some heat out of the heating system, so we’d boost the operating temp a bit for the winter. Modern cars already operate right on the brink of pinging, so it isn’t necessary any more.


Oh, and (in better explaining) blocking the radiator blocked the cold air from passing through the radiator and from passing by the engine dissipating heat, thereby helping the engine warm up. At -20 degrees ambient, it’s needed.