PT GT blowing water into overflow when normal temp?

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..

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

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.

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

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.

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

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.

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

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.

sounds like a cracked head, just went through that on an 06 cruiser. temp would never go over 1/2 but would boil out of overflow. radiator had small leak, and low speed on fan was bad, that originally caused the overheat and crack in head. replaced radio, cap, and fan, runs 1/2 temp, but after 5min of driving starts pushing water out of bottle. have to put a gallon a week in.

If it was a cracked head wouldn’t the car run like crap ??? Idk just asking

I’m having the same problem. I even flushed radiator out plus car has new head gasket, thermostat, electric fan and water pump. Any suggestions would be nice