coolant problems bypassing cap HELP

stangaddict2007

New Member
Nov 13, 2007
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Ive got a 90 mustang gt I just put a new 306 and t5 swap , The problem is the car is spewing coolant past the radiator cap and filling the resevoir and overflowing, This is my 11th mustang and Ive never come across this before, Heres what the car has done 4 core jegs rad., two electric fans, new water pump, new 16lb cap, new 160 thermostat, new water pump hoses , old radiator hoses swelling under pressure,Under drve pulleys, short belt bypassing smog pump, Car reads 150 - 170 degrees on autometer gauge The car had this problem before swap but not as noticeable, In my opinion the fans are 2 small, the radiator could use flushed, the cap may be 2 short or not strong enough , any help greatly appreciated, THANKS
 
Mine puked coolant all over as it was burpin out air bubbles when I was filling the system. Have you run it for a while and it just started doing this or just put it together?
 
I'd suspect the cap of being faulty.


The coolant is overheating and expanding and passing by the cap which is supposed to pressurize the system. Some coolant should fill the overflow, but not enough tocome out. Usually just enough to raise the level 4-5 inches in the bottle