Classic cars forum & vehicle restoration.
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Jim.Walker
Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield
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 Posted: Wed May 25, 2011 2:17 pm Post subject: |
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| alapimba wrote: | how the thermosyphon works?
i have a sidevalve engine but didn't realized how it works and how to check if it's working as it should before overheat the engine.
anyone can explains? |
Quite simple really. Hot water, like hot air, rises. As along as there is a predominently upwards path to the header tank from the engine, where it warms up, it will want to flow to the header tank. Of course the water in the radiator core is cooling and wants to sink to the bottom of the radiator. And so circulation is by "Thermo Syphon". The higher the radiator header tank is above the heat source (engine) the better and conversely the radiator bottom tank should be no lower than the heat source than is necessary to fit it in.
Jim.
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Jim.Walker
Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield
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| Posted: Wed May 25, 2011 2:31 pm Post subject: |
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| Penman wrote: | hi
The top hose is actually vertical, the horizontal bit just means that you have a bigger than normal header tank.  |
That is so Penman, but the actual height difference between cylinder head outlet and header tank is still not enough for satisfactory thermo syphon action. Compare that with the type of car the engine came from. Which would have had a much higher bonnet line and header tank. Of course the waterpump should help provided it pumps sufficient water. However, the sharp corner will not help circulation. That long horizontal path for the water from the elbow to the header tank probably does not help either (flow friction), and the (still hot) water sitting in the horizontal part cannot rise any further to aid circulation. Also many T/S cars had a tapered top hose. Can't see how, but I wonder if there is a practical reason for that.
Maybe a smaller pulley on your waterpump to speed up its rotation would help?
Jim.
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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alapimba
Joined: 03 Dec 2007
Posts: 181
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| Posted: Wed May 25, 2011 2:54 pm Post subject: |
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| Jim.Walker wrote: | | alapimba wrote: | how the thermosyphon works?
i have a sidevalve engine but didn't realized how it works and how to check if it's working as it should before overheat the engine.
anyone can explains? |
Quite simple really. Hot water, like hot air, rises. As along as there is a predominently upwards path to the header tank from the engine, where it warms up, it will want to flow to the header tank. Of course the water in the radiator core is cooling and wants to sink to the bottom of the radiator. And so circulation is by "Thermo Syphon". The higher the radiator header tank is above the heat source (engine) the better and conversely the radiator bottom tank should be no lower than the heat source than is necessary to fit it in.
Jim. |
It means theres no special part installed inside of the engine for it happends, right? As long has the radiator is clean and nothing is stoping the water to flow everything will do his job? I'm asking this question because on my model Y with e93a engine today my mechanic said that maybe would be a good idea to install one of that period water pumps to don't have any problem. As long as i understand the thermo syphon only works when the water is boiling, it means at that point the engine is allready too hot and can have damage, no? |
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Jim.Walker
Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield
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| Posted: Wed May 25, 2011 5:33 pm Post subject: |
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| alapimba wrote: | | Jim.Walker wrote: | | alapimba wrote: | how the thermosyphon works?
i have a sidevalve engine but didn't realized how it works and how to check if it's working as it should before overheat the engine.
anyone can explains? |
Quite simple really. Hot water, like hot air, rises. As along as there is a predominently upwards path to the header tank from the engine, where it warms up, it will want to flow to the header tank. Of course the water in the radiator core is cooling and wants to sink to the bottom of the radiator. And so circulation is by "Thermo Syphon". The higher the radiator header tank is above the heat source (engine) the better and conversely the radiator bottom tank should be no lower than the heat source than is necessary to fit it in.
Jim. |
It means theres no special part installed inside of the engine for it happends, right? As long has the radiator is clean and nothing is stoping the water to flow everything will do his job? I'm asking this question because on my model Y with e93a engine today my mechanic said that maybe would be a good idea to install one of that period water pumps to don't have any problem. As long as i understand the thermo syphon only works when the water is boiling, it means at that point the engine is allready too hot and can have damage, no? |
Not quite right. As soon as the water heats up there should be thermo syphon circulation, which makes the water flow upwards through the engine and downwards through the radiator to cool the engine. The engine should not boil. If it does it probably means that the system is clogged with dirt or scale. Unless you live in a very hot climate. Or drive up VERY long hills.
Retarded ignition timing can cause boiling and so can too small valve clearances - particularly on the exhaust valves. A weak fuel mixture also causes overheating.
Your car was built with no water-pump and has run many years without one. So if no changes have been made to the engine and cooling system it should not boil now.
Boiling will not normally cause damage as long as you do not continue driving with it boiling.
Jim.
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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Penman
Joined: 23 Nov 2007
Posts: 4756
Location: Swindon, Wilts.
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| Posted: Wed May 25, 2011 8:50 pm Post subject: |
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Hi
The water in the engine gets HOT, hot water rises to the highest point in the system (The header tank) cold water from the bottom of the radiator (design to cool down the water) enters the engine through the bottom hose frrom the bottom of the radiator (The coolest part)
Do you remember when people had mufflers, or a piece of cardboard, over the bottom of teir radiator in feezing conditions in the winter?
This was because until the engine had warmed up the wind chill effect through the rad could actually freeze the bottom of the rad and thuis stop the circulation, possibly more likely to happen with a pumped system with a thermostat.
The direction of circulation is identical with that of a pumped system., pumps became essential with the advent of water supplied heaters but would also aid circulation if an engine suffered from isolated hotspots.
Early heaters always used a water valve to stop circulation through them, but they took a time to warm up when switched on, most, if not all, modern heaters keep the water circulating and have flaps which divert fresh air either through them for warmth or bypass them for cold air, which means virtually instant warm air when required providing the engine is up to temp.
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roverdriver
Joined: 18 Oct 2008
Posts: 1210
Location: 100 miles from Melbourne, Victoria, Australia
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| Posted: Thu May 26, 2011 10:31 am Post subject: |
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alapimba, think of it this way. After trying pumps on his earlier cars, Henry Ford found that the natural water circulation, that we call 'thermosyphon' was quite sufficient to keep the engine temperature within bounds. The model T had no pump ex-factory. With the UK small-engine cars, they also ran with no water pumps, and even in hot Australia they managed very well.
It is important that all water passages allow for a free flow of water, including, of course, the radiator. A car fitted with a water pump might be a little more forgiving with partly blocked water passages, but if you look carefully you will see that the Y radiator is much bigger than you would find on any car with a water-pump fitted.
Boiling does no harm provided that there is still water above the level of the cylinder head. If you have to operate a car that constantly boils (as I have done on many occasions), just keep topping up the radiator as frequently as required. Best to get the problem solved as soon as possible of course, but you will do no harm.
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