I was testing my cooling system and added a small piece of rubber to the radiator cap. It was the rubber of an older cap I had lying around. It brought the opening pressure to about 25 psi. I took the car out for a 15 minute drive and the temp was pretty stable at I guess 185. The needle never really moved from the letter "M" which in the garage is about 185 degrees. Either way in the morning it took a look and the upper radiator hose caught my attention. It was flat like a sideways pancake. I popped the cap and the vacuum escaped and the hose's shape returned. What on earth would cause that?

 

That's because hot coolant expands and causes pressure and when it cools it creates a vacuum. By adding rubber to the cap you caused it to be airtight and not allow the system to draw either air or coolant from a catch can back into the cooling system. It breathes in a weird way.

 

Hey thanks,

 

I would add that if you drove it around last night and checked it, I would bet the upper hose was either rock hard or bulging from the pressure.

 

It always is. I didnt realize when I purchased the waterpump it had a clause stating it would raise system pressure. At 16 psi it lets enough coolant out to **** me off and pull over and let it cool. I need a cap in the mid 20's to keep it all in. I got the goodyear hi miller hoses(thank god) and I am hoping it holds.

 

I'd be more concerned about whether your radiator, heater or cooling system gaskets could take such excessive pressure.

 

I talked to the radiator people yesterday, and I got a thumbs up.
They actually suggested removing the tstat to get the pressure back down instead of increasing the pressure. But they said it could take it if that what I needed to do. I dont know about the gaskets? What gasket should I be concerned with?

 

I am switching to dakota digital dash. So I will know for sure whats going on. Right now I am based off of the temp gauge. It starts to clmib and I start to sweat. I just replaced the engine cause i drove it while it overheated. So I am going with a digital gauge with numbers so I know exactly what is going on.

 

A standard cap is 13lbs correct? I wouldn't want anymore pressure than the specs state. I would take the extra rubber off the cap. Chances are you have overfilled the system and it's just spitting the extra out. Get a coolant reservoir
and let it cycle normally. Pressurizing the system won't keep it cooler, just allow it to run hotter without boiling as easily.

 

I got a 16 pound cap that came with the radiator. I have had nothing but trouble trying to find a replacment cap. That radiator is a sob and only take its own cap!!! I should have stuck with a standard waterpump. That where i shot myself in the foot. I went with the high flow version. I am trying to make this all work but am having a hell of a time .Also the uncertainty of the temp gauge adds to the frustration. With the extra piece of rubber the gauge sits in the middle. without it and 10 min drive its almost passed the P. I know it runs a bit hotter but the way the temp gauge works each ohm on the top end really gets the gauge moving.

I thought a 13 pound cap came with a cooling system that ran 165 degree tstat.