coolant boiling in reservoir

[2GFWDbeast]

i have a 97 gst with 25xxx on rebuild motor.so i popped my hood and noticed the overflow reservior was full boiling but it only happens when im boosting if i driving around normal it dont fill up my car did over heat but that was do to thermostat the car runs at normal temp. theres no white smoke or coolant mixed with oil my compression is 175 across board. the top radiator hose is super hard like has ton of pressure in it and u can feel it bubbling in the hose could i have a bad radiator cap? or am i pushing coolant at boost im boosting 20psi on a t28. cause it never happened when i had 14b turbo on the car. i dont think the fan turns on i let car run for like 10min at idle and fan never turned on. i bought the car it only had one fan on it someone took the fan that is on the driver side and put it on the passnger side of the radiator so i only have to the fan on the passnger side.

 

[Afroclipse]

Stick your finger in the overflow, If it is really hot it is boiling.

If its not hot but warm your car is pushing coolant which is a bad HG.

Don't listen to this guy he doesn't know what he is talking about, due to the high heat the finger will not get an accurate reading on whether it is boiling or not. What you want to do is remove the coolant resevior and splash the water on your face, that way you will tell whether it is really hot while tasting for unwanted minerals like small rocks, oil, shaving e.t.c. If your face melts then yes it is boiling, if you only turn pink from burns then its ok, but if its cold then you need to make a few pulls and repeat procedure. Hope this help in your diagnosis.