So if thermo-syphon was the way to cool a Model T - would the system work and be just as efficient if - on enclosed cars - a liquid heater would be added to the cooling system. Or is the water pump necessary to have fluid pass through the heater.
My guess would be that the heater inlet should be from the pipe and the outlet should go to the outlet from the head. I expect that would produce thermosyphon through the heater circuit.
I have wondered the same thing. Most cars of the T era used some sort of exhaust heater and any T's that I have seen using water to heat the car had a pump on it. ( ok "car" but it's the only one I have ever seen )
I would think it would be a bad idea unless the heater were at the very lowest point of the system. Thermosyphon works by cooler (therefore more dense) fluid sinking to the bottom of the system and displacing the warmer (less dense) fluid, pushing it upward. If the heater were anywhere but the very bottom and you removed even more heat from the water (Say by blowing air across it to send inside the car), that water becomes more dense than it was and tries to sink lower in the system. Put it in the upper hose, and when the "Heater" cools the water, the water will want to fall back down inside the head. Put it in the lower pipe, and when the "heater" cools the water, it tries to fall back down into the radiator.
If the fan were not in the way, it would probably work best to try to duct some of the air that has come through the radiator to inside the car. It's probably been tried. Probably didn't work well enough and that's why the manifold heater was more prevalent.
Just my speculation.
Actually Hal some of the "manifold" heaters have an air funnel facing forward protruding from the front end of the manifold heater sheet metal or casting. That part of the heater thus funnels in the hot air coming from behind the fan and uses the radiator fan thus as the heater fan. The air that passes through the radiator is further heated as it passes on over the manifold and finally into the passenger compartment through a floor board "register" that can be opened or closed.
You're right John. I had not thought of it quite like that, but the manifold heaters do indeed take air that has already been warmed by the radiator and warms it some more by putting it across the manifold. I have one on my Model A (Well, when it's cold I put it on), but it is marginal at best.
For about 35 years my daily driver was a car with a manifold heater. You could add a JC Whitney fan to help it out a little.
On a long trip in cold weather, you would be almost comfortable in a couple of hours. It's remarkable that a country which gets as cold as Germany produced a car with such a miserable excuse for a heater.
It wasn't common with heaters in cars during the 20's, so liquid heaters weren't developed yet. They became more common during the 30's and in Sweden heaters became standard equipment during the early 50's.
The English Ford Anglia was among the cheapest on the market and kept 1930's mechanics well into the 50's. The little sidevalve engine had thermosiphon cooling. To equip a 1949-53 Anglia with a heater you also had to add an accessory water pump, driven from the outside of the fan belt