Question? What is over heating of a Model T Ford? There have been comments about how the thermosyphon works, the evils of the water pump, how to read a Motometer, but without a head temperature gauge or modern style heat gauge, how do you know - first time owners - when the car is over heating? If a "normal" temperature is around 200dF, then a bit of steam, or over flow from the filler cap is normal. Filling the radiator full will give the impression of over heating when the liquid starts to bubble out of the over flow of around the radiator cap. Steam starts to appear around 180 - 200 dF.
Spend 20 to 40 dollars for a heat indicating gun.
They are very accurate and fast. I have a mechanical gage on the bottom of the dash tapped into the outlet on my block. Its easy to see comparison from a moto meter through the radiator with those tools. As far as the CORRECT temperature there are many different opinions.
Yes, over filling the radiator will give the appearance of overheating. I've always believed that if its not boiling it's OK. Sometimes in hot weather you'll get some gurgling at low speeds and when you turn it off, but generally as long as you do not get a sustained boil you should be fine.
I imagine others will have more scientific answers, but for the most part running and driving our T's is more art than science. This is just one example of the artistic side of things. As you said, there's no head gauge or modern style heat gauge, so you must rely on other less definitive indicators.
Just my $0.02 worth.
A heat gun will check any part of a head, radiator, block, pipes, running or not at any time in one second. Much better then Henry had and much better then my mechanical gage except the mechanical gage can be seen from inside the car continually.----------another opinion!
For what it's worth Paul,....your cost estimate of a heat gun is "right on", and I've seen them "on sale" recently at Harbor Freight Tools for less that $30.00!
Again, "FWIW",....using a heat gun to compare the temp of the upper radiator hose & outlet fitting on head, to the temp of the lower radiator hose & inlet fitting on side of engine block is a really good indicator of what the radiator is, or is not doing. Not sure right now what the temp difference should be, or, one might say,....the acceptable temp difference "range", but again, this is a really good test of radiator efficiency.
The indicator of overheating are these:
If you have the original type cap and the gasket is not completely sealed, you will see steam coming out around the cap. If it is completely sealed, the steam will come out the overflow tube on the left side of the radiator and you will see steam coming from under the car or under the hood. If you have a motometer, you will see the red all the way to the top of the thermometer.
The overheating is usually worse with prolonged idling or when pulling a steep hill.
The car is just a "wanna-be a Stanley!"