Add coolant overflow to 225?

whitepunkonnitro said

The type of radiator you have dictates whether or not an overflow bottle is necessary. Earlier rads used a very large upper tank. These are only supposed to be filled to the top of the tubes, and the extra space is for expansion. Later rads, 73 up used a smaller tank that is supposed to be filled all the way, and these use a recovery bottle.

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No, sir. In terms of capacity, the earlier round-top tanks aren't so much bigger as they look than the later square-top tanks. And many, many cars left the factory deliberately equipped with small square-top tanks and no recovery tank. The switch from round-top to square-top tanks was made because the radiators were easier and cheaper to make (and make leak-free) with the square-top tank design.

No matter what shape the radiator tank is, if you don't have a recovery tank, you have two choices: either you stop filling the rad when the fluid level's about an inch and a half below the neck, or the radiator will correct itself to that level once the engine's reached operating temperature a few times, with the overage hitting the ground via the overflow tube. And if you do have a recovery system, either you fill the rad right up to the neck or—assuming there's fluid in the recovery tank—the radiator will correct itself to that level once the engine's cooled down from operating temperature a few times, and you'll find the level lowered in the recovery tank.

Refer to the link in post № 13 of this thread.