Started my evo up last week, and about 10 minutes into my drive i notice it starting to overheat. i check my coolant, and im empty. i refill, and take her for another drive. same thing happens. i notice that what was happening was pressure was building in my radiator, forcing all the coolant out of the overflow.

immediately i think head gasket. So i get a pressure test done, and everything is fine and im not losing any pressure. i replace the thermostat as well, and im still having the same problem.

is it likely that the headgasket is still bad despite not losing any pressure? or maybe water pump?

id like to get some ideas before i get into tearing the head apart. Any insight would be appreciate

 

I had a similar issue on an old dsm. Every pressure test and block test (fluid) came back negative results till I thought, maybe it only leaks while I'm hot doggin it.
I put the big plastic funnel thing on my radiator, filled it half way up and held the 2step for about 6 seconds and sure enough, it started burping massive ammounts of exhaust gasses from the radiator.

It would never loose coolant or overheat if I babied it but a few minutes after hitting boost it would get hot.

 

mine seems to be blowing all the coolant out of the overflow regardless of how much i baby it.

did you end up finding out what your issue was?

 

Thinking HG as well, cant build pressure anywhere else except the block. It may be that under no load testing, nothing happens, pressure tested under boost forces exhaust past the gasket.. if you go this route-- dont forget to surface the head and clean the block

 

Mine was head gasket leakage rooted from a lean overboost condition and an imperfect head surface.