PT GT blowing water into overflow when normal temp?

Ed Kyle

Asked by Sep 09, 2015 at 02:05 PM about the 2003 Chrysler PT Cruiser GT

Question type: Maintenance & Repair

I've replaced the head gasket,radiator, took thermostat out, new 18 lb cap. Can
you install a higher pressure cap then the 18 lb?

11 Answers

Ed Kyle

BTW, the car runs great, no overheating at all until it starts running low on water at about 100 miles. It will boil out a gallon /100mi


Adding more water than coolant will decrease the boiling point, do you have a 50/50 mix? did you bleed the system, check to see if the return may be clogged..

Tom Harmon

My calculations are coming out to an engine temp of well over 245f. so you are well above the safe heat range of that engine. You must have a small leak in your cooling system ... if you put a cap on that's any higher then you will either blow the radiator core, the hose or both ... I would never go higher than 15 lbs ... Have the radiator pressure checked ... I can guarantee your not sealed

Ed Kyle

I originally bled the system, then decided to remove thermostat completely, well took center out of it, so, no air in system problem, and yes, it would take a water temp of 245* to open an 18 lb cap, so why would the water get thru the cap at normal operating temperatures. Bathroom scales confirm that the cap does take 18lbs to open. Still baffled.

Ed Kyle

Oh, and it did the same thing with a 50/50 mix. Straight water now what with using a gal/100 mi

Ed Kyle

I suppose that if it's getting combustion gas into the water system that it would be easy to open the cap. It doesn't show anything like that at idle with the cap off.

Tom Harmon

You still have a small leak ... Here is the clue "Water cannot boil under pressure"

Ed Kyle

And even w/o pressure, it wouldn't boil before 212*, but I know it's blowing out all around my new cap and filling the overflow bottle. It will idle forever w/o overflowing or dropping any water on the driveway.

Tom Harmon

When water ( liquid) boils it expands to about 3000-1. To prevent water from boiling it becomes pressurized over 211F and remains a liquid because you can't cool anything with steam. If you know any steam pressure you can find the temperature by going to a "steam Table" thus 18 lbs of steam is about 250 degrees F. To me, it's obvious that you only have over 18lbs of pressure or the coolant would not go to the overflow. ... that means the water is boiling inside the radiator then the expansion is increasing pressure .... your system has a small leak

Ed Kyle

Yep, and it must be an internal leak into the cylinders which is being burned off slowly because there is no white smoke


Is the electric fan working? Turn on the AC and test it. Fans run during AC, that is if the compressor actually works too. There's a pressure sensing switch on the high side of AC that signals the fans ON. No pressure ... no fans either.

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