I have a 94 f-250 7.5 255,000 miles I have a problem with my cooling system building so much pressure that it fills the overflow almost immediately and the starts puking out of the radiator cap and when I shut the truck off it sounds like the coolant is boiling while it pukes out I have checked for combustion gasses and the test came back negative had a new water pump and thermostat put on about 5 years ago and a new radiator about 4 months ago I usually lose about 2 gallons of coolant in 2 weeks from this the truck runs cool mostly itll warm up slightly more while at idle but not enough to be concerned does anyone have any info that might can help me here

 

Could be as simple as a bad radiator cap. The sad part is many are bad right out of the box.

 

Sounds like it is running hot. You should probably check it with a proper gauge.

 

How long does it take before the overpressure starts?