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 Radiator

 Created by: Portvegas
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 Posted: May 5, 2019 06:50AM
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might be the water pump. easy to replace it.. I also upgrade to the Alloy rad. when I replace one..about $45 for one now.. later bc

 Posted: May 5, 2019 04:29AM
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CA
That is correct.
On this type of radiator, you do not fill to the top, but leave about 1" of air space - the cores should be covered by at least 1/2" of coolant when cold. The air space does two things. It allows for expansion and provides for an increase in internal pressure. The radiator cap is a pressure type. It holds the air in until the cooling system reaches the intended pressure. (The pressure raises the boiling point of the liquid.) Under normal conditions, no coolant goes to the over flow hose as its connection is outside the pressure seal. If your engine overheats, it produces steam, which increases the pressure beyond the cap's set point. When that occurs, the cap releases, venting steam or liquid coolant.

In a car that is functioning properly, overheating is sometimes caused by a low coolant condition. If you put too much coolant in, it expands and pushes the excess coolant out the overflow. The hose is there to drain it away from the engine bay. When the engine cools down again, the rad cap has a reverse vent to let air back in so atmospheric pressure doesn't collapse the radiator. You don't really need a catch tank because you want air to come back in to provide the needed expansion space.

If you think you can add an expansion tank and fill the rad up, you would be defeating the system - the hydraulic pressure of the expanding coolant would force the pressure cap open each time and require its venting return valve to function each time. probably gumming it up. Pressurization of the system would also have to rely on the hoses stretching.

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"Hang on a minute lads....I've got a great idea."

 Posted: May 5, 2019 03:20AM
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I was trying to investigate where a leak was coming from and end up finding the radiator overflow hose was cracked, right at the neck of the radiator.  My question is, do most minis not have an overflow tank? It looks like the hose dumps directly to the ground.