ok last couple of days its been warm out and my car has been sitting at 1/3 of the way up to overheating. Today, the temp gauge was all over the board, overheating, normal and everywhere inbetween. when im at like 3k in fifth gear the car gets hot even thought im doing 60, drop it in 3rd and it cools down. and when i romp on it it cools down, but at a stop it gets hotter or if im just cruisin.

I stopped and hit the pressure vent on my rad and a ton of boiling water came out.

I got a crx b16a t3/t4 with cometic headgasket and arp studs, the rad is a new 79 civic half rad (maybe too small) but is wierd because it does it every once in a while. It would do it on a colder day compared to a hotter day

Any ideas?

 

thermostat broken, coolant low, fan not working, bad radiator cap???