The Missing Thermostat

Feb 08, 2022

Are you ready to get a new puzzler? Here it is.

A customer came in the other day. And he said, "Hey, guys," he said, "I was looking under the hood of my car. And I noticed something interesting."

He said, "I decided it was time to flush the cooling system and all that. And I've done this in other cars and when I usually do it, I take the thermostat out and I put a can of fast flush in there. And I let the environmentally unsound ingredients from the flush and antifreeze go down the sewer."

But he said, "Here I am, ready to take the thermostat out and I can't find the thermostat!"

Now for about a millennium or maybe a little longer, thermostats have always been located right where the top hose attaches to the engine, the top radiator hose. So if you wanted to find the thermostat, you'd find the radiator, which is that big black thing in the front of the car. And you would find the hose that attaches to the top of that. And you would follow it to the engine and voila, under that little water outlet, or thermostat housing as it's sometimes called, there is the thermostat.

(That's why it's called the thermostat housing--it houses what the thermostat.)

He finally does find it but it is located in the bottom hose. He follows the bottom hose to the engine and there is the thermostat.

So after saying, "Sonja Henie's Tutu!" he wonders: why is the thermostat in this car (and this there are many cars that have it like this I mean all Hondas and many Toyotas and there are many, many cars on the road, modern cars that have the thermostat located in the bottom hose and not the top hose) why this change? I mean for so many years it was the other way around. Why did they change and there were two reasons.

Reason 1 and reason B, and we want both of them!



The reason the thermostat is located in the bottom hose on many modern cars is, cars that have aluminum cylinder heads used to have a big problem with cylinder heads warping and head gaskets blowing and all that stuff. And they figured out a way to solve it is to make the coolant circulate the other way.

The way it used to work is the hottest stuff would leave and go fall down through the radiator and then when it got to the bottom of the radiator, it would come back into the engine. But that was when the cool part was down at the bottom instead of being up at the top.

That had an initial disadvantage because the cool water being at the bottom will make the engine run inefficiently because the cylinders were too cool to have really efficient combustion. So this solves two problems. It keeps the cylinder head cool by having the coolant, the coolest coolant comes to the cylinder head first. And by the time it gets heated up by that hot cylinder head, it flows into the block where it's the hottest, and it makes the engine run most efficiently.

It's one of those things where you say how come it took 100 years to figure that out?

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