Radiator Hose Vacuum?
 

I was drifting my S4 TII last night and shut it down when it was getting a little warm. The coolant overflow tank was bubbling a little and when it cooled down my upper and lower radiator hoses were sucked in like a vacuum. I thought that they should have been building pressure not a vacuum when it gets warm. Any idea what could cause this?

-Aaron

You said sucked in when it is cooling. Radiator cap is not allowing coolant to flow back in causing the vacuum.

So replace the radiator cap? I've got a new Koyo on the way. Replace the cap when I replace the radiator?

Sounds like that is the problem. Coolant gets hot and expands and goes to the over flow tank. When it cools it creates a vacuum. If the cap is stuck down it can't suck the coolant back in and makes the hoses collapse. Make sure the hoses are in good condition as well. If they are really soft it might be replacement time.

Ok, thanks for the information, it's greatly appreciated.

-Aaron

Resurrecting an old thread for help...
 

The exact same thing happened to me this weekend, only I have a brand new radiator cap from Mazdatrix (also replaced the thermo). I'm having some horrible problems with my cooling system and this is just one of the hair pulling issues I'm having. Buzzer goes off, temp gauge goes up and down, sometimes she spills out at the overflow bottle?!?

you probably have a leak somewhere or you have air in your cooling system and need to bleed it.

I have drained the system several times trying to eliminate all possbilities of just contaminated coolant blocking up the system. So it is certainly possible for air to be in the system. Is there a bleeder valve to get rid of the air? Could air in the system be causing all the mentioned problems though? What about the water pump, any way to test that?

there is a little bleeder screw on the stock rad where the tube attaches at the top of the rad when you fill up the rad undo it and fill it up untill coolant starts to come out then block it with your finger till the air is out and the coolant stops coming out. after that start the car with the heater on full blast

Go to Advance Auto Parts and rent their cooling system pressure tester. it's an expensive deposit that I didn't feel like putting down, so I left a card with them for an afternoon while I had the tester