Cooling system basic operation - Honda Shadow Forums : Shadow Motorcycle Forum
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post #1 of 32 (permalink) Old 01-17-2019, 01:51 PM Thread Starter
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Cooling system basic operation

The cooling system is very similar to the modern automobile in operation. If it has the correct cap it will return flow and keep the radiator full to the top. Here is the operation of the cap.



The large rubber seal keeps the pressure in the system and doesn't let it leak outside.
The small rubber seal allows the pressure to overcome the spring and flow into the res tank when it heats up and expands. It also seals when it cools down and the fluid contracts and flows back into the main system.
And the metal disc is a one way valve to allow the return of the fluid and sometimes is gummed up and sticks and doesn't allow the return fluid back in.
Make sure all of those are in good condition. These are designed to keep the radiator completely full of coolant.

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post #2 of 32 (permalink) Old 01-17-2019, 01:56 PM Thread Starter
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A simple video explaining the radiator, thermostat, pump and recovery operations.

Of course car parts are larger and have different pressures.
But the principles are the same.





Only a biker knows why a dog sticks his head out of a car window.
1983 750 Shadow
From the past=
1951 Cushman scooter
1962 Honda 305 Dream
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1971 Honda 175 scrambler
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post #3 of 32 (permalink) Old 01-17-2019, 02:11 PM
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Good information!
Phil


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post #4 of 32 (permalink) Old 01-17-2019, 02:50 PM Thread Starter
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In the old cars up to about the 1960's the radiator cap was a pressure only. You had to leave the coolant level down a couple of inches so it could expand when it heated up . Then dropped again as it cooled down. Modern cars use the recovery system to keep as much coolant in the radiator to take advantage of the air flow/liquid cooling available. The cap is important more so now , not just a stopper.

The pressure spring of the cap will cause the boiling point to increase above normal water of 212 degrees.


Coolant is important as a liquid cooler, but also causes the boiling point to increase.



The thermostat can be in constant motion as a valve . When the temp in the engine goes up it opens fully but if the temp lowers (on a cold day putting around town), it may close some to keep the temp in the engine where the engineers design it. Many modern engines run up into the 200 degree range . They warm up faster also for efficiency and cleaner emissions.


The overflow tank should be about 1/3 full cold so it can receive and return coolant. Just a reserve supply tank.

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From the past=
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1962 Honda 305 Dream
1965 Honda 305 Dream
1971 Honda 175 scrambler
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post #5 of 32 (permalink) Old 01-17-2019, 03:24 PM
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In the opening statements the author mentions that "a fluid; mostly water" is used. While this is true since some coolants contain water, it may be misleading as most of us will use a 50/50 mix of coolant and water. Also most of us will have an electrically operated fan motor that cycles rather than a belt driven fan so we have a slightly more complicated cooling system that includes a fan, fan motor, fan motor switch (and a thermosensor and coolant temp indicator to let us know we are overheating!)

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post #6 of 32 (permalink) Old 01-18-2019, 09:12 AM
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The gasket on the radiator cap is there to insure the cap is screwed down tightly on the throat of the radiator. This keeps coolant from spilling out of the radiator and also prevents air from infiltrating the cooling system.



A spring loaded pressure relief valve is housed in the radiator cap. The valve is spring loaded at 16 psi.




As the coolant in the radiator heats up, it creates pressure inside the radiator. When pressure inside the radiator exceeds 16 psi, the pressure valve opens and coolant flows to the coolant reservoir tank (green arrow).




The radiator cap also has a vacuum valve which is housed inside the pressure valve and is also spring loaded. Like the pressure relief valve, the vacuum valve is a one-way valve but operates in the reverse direction.



As the coolant in the radiator cools, it shrinks in volume, which, in turn, creates a vacuum inside the radiator. The vacuum pulls the vacuum relief valve down and siphons coolant from the reservoir tank replenishing the coolant level in the radiator (green arrow).

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post #7 of 32 (permalink) Old 01-18-2019, 11:55 PM
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Can one assume it's a self regulating system then? Here's another question.

Let's say the cooling system is completely drained and you fill it to the rim, through the filler hole. You're then supposed to run the engine for a bit without it fully heating up, allowing the coolant to be picked up by the pump. Level will drop so, you basically want to keep filling up until you're seeing coolant in the reservoir which would indicate a topped up system.

Now, instead of taking the filler cap off for the top-off so to speak, can't you leave the engine running and just keep filling the reservoir instead? Until the system doesn't take up any more?
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post #8 of 32 (permalink) Old 01-19-2019, 12:10 AM
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Quote:
Originally Posted by AmsterDan View Post
Can one assume it's a self regulating system then? Here's another question.

Let's say the cooling system is completely drained and you fill it to the rim, through the filler hole. You're then supposed to run the engine for a bit without it fully heating up, allowing the coolant to be picked up by the pump. Level will drop so, you basically want to keep filling up until you're seeing coolant in the reservoir which would indicate a topped up system.

Now, instead of taking the filler cap off for the top-off so to speak, can't you leave the engine running and just keep filling the reservoir instead? Until the system doesn't take up any more?

If you add it to the reservoir, it will have no way to climb up hill and get into the radiator. The radiator will be hot and starving for water and it will open up the pressure relief valve in the cap, but that will only let the excess pressure out of the radiator.
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post #9 of 32 (permalink) Old 01-19-2019, 12:15 AM
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Ron's diagrams above explain this perfectly.
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post #10 of 32 (permalink) Old 01-19-2019, 02:39 AM
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Understood. Thanks much for the dedicated thread!

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