I have a S4 TII with 2300 miles since rebuild. The car has been running real good with no problems. Today my coolant buzzer went off and noticed coolant was coming out the thermostat neck nipple. I have a regular non pressurized cap on it. I have a pressurized cap on my koyo radiator. I swapped the caps so the reg cap is on the radiator and pressurized cap is on the filler neck and drove for 15 min with no problems. When i shut the car off i noticed coolant coming out from the overflow bottle. The coolant will leak wherever i install the non pressurized cap. Should i buy another pressurized cap and will this fix the prob? The reg cap is figure (H)

 

Where does your overflow tank pipe into? The t-stat neck or the rad?

Whichever one, that's where the pressure cap needs to be...

 

The overflow tube is on the radiator. I installed a new cap on the radiator today. The thermostat neck cap needs to be pressurized also right? Also the nipple on the thermo neck is not going to anything. I just installed a new cap on the radiator and nothing comes out of the overflow now. I think my problem is my older pressurized cap is installed on the thermo neck and that is dripping now after i shut eng off.. I'll buy another 13lb cap tommorow.. Will keep everyone updated...

 

Yeah, I think you got a handle on things now.

I use a pressure cap on my t-stat housing, but only so I have a spare with me in case the rad cap fails. All you really need is a flat cap there...