radiator overflow after it sits for a while

[sport fury guy]

I have an issue with my 67 Sport Fury Vert puking out antifreeze after it has sat a while, it does not run hot. What is causing this?

 

[300rag]

This is normal. After the engine is shut down, the heat soak from that hot block will continue to heat the coolant and it will puke it out. When it has cooled, the level of coolant in the rad should be about an inch below the filler neck. This is the "full" mark. If you top it up, it will do the same thing the next drive.

 

[sport fury guy]

Thanks, figured it was nothing to worry about, but thought I'd better check.

 

[Toolmanmike]

I have an issue with my 67 Sport Fury Vert puking out antifreeze after it has sat a while, it does not run hot. What is causing this?

How full is your radiator? It should be a inch below the bottom of the neck to give the coolant a place to expand. These old systems don't have a overflow tank. I would replace the radiator cap. If it looses pressure quickly after the engine is shut off the coolant will superheat and boil over.

 

[1970FuryConv]

If you want to fill the radiator and the neck has a hose fitting, you could add something like this. Advance 603001
Advance Auto Parts - Down for Maintenance

 

[stubs300]

I would replace the radiator cap. If it looses pressure quickly after the engine is shut off the coolant will superheat and boil over.

You're contradicting yourself! Pressurizing a system raises the boiling point of water! If the cap leaks that quick and the water level's low enough, there's no way in hell that it will superheat and boil over!

 

[Toolmanmike]

You're contradicting yourself! Pressurizing a system raises the boiling point of water! If the cap leaks that quick and the water level's low enough, there's no way in hell that it will superheat and boil over!

If the conditions are right and the cap leaks, the system will maintain the pressure as long as the engine runs. When the engine is shut off and the pressure bleeds out quickly through a leaky cap, the boiling point goes from 250°+ back to 212° in short order. (3° rise in boiling point for each pound of cap pressure.) I have seen it happen numerous times. I could drive my 70 for hours and as soon as I stopped it would puke coolant out. I pressure tested the system and the cap and the cap wouldn't hold pressure. New cap and no more hot soak puking. A healthy system with a working cap, you should be able to release pressure after it sets for a hour or so. It will hold it for at least that long.