2002 Honda Civic...The car is overheating randomly. Replaced the thermostat,and fan relays. Car runs fine and then randomly overheats with gauge going way up and then sometimes coming down.Overheating and blowing out coolant around the overflow container. Seems to act up on hills and stopped in traffic. Two mechanics are stumped..they both say there is no sign of head gasket problems...HELP

The most common overlook thing is you got a air pocket, so before you go spend your money turn Heather on full blast, open the radiator cap, car running look for air bubbles, takes patience cause you got to wait for the thermostat to open up, you must refill the coolant really really slow snail pace, some car have a bleeding valve others have two chamber on the overflow bottle,good luck, if that doesn't work change the thermostat first and if that doesn't work I'm afraid you may need to replace water pump. . water pump

RADIATOR COOLING FAN NOT RUNNING COULD BE BAD ENGINE.COOLANT TEMPERATURE SENSOR IS FAULTY IF COOLING FAN IS NOT TURNING ON AT SET TEMPERATURE OF 196 TO 203 DEGRESS.CHECK SEE COOLING FAN RUNNING WHEN ENGINE RUNNING HOT.IF YES FLUSH RADIATOR , FLUSH ENGINE BLOCK, HEATER CORE,REPLACE RADIATOR CAP.MAKE SURE YOU HAVE 50/50 ANTIFREEZE AND WATER IN THE COOLANT SYSTEM.CHECK WATER PUMP WEEP HOLE IF LEAKING REPLACE WATER PUMP. IF COOLANT FAN DONT TURN ON 196 TO 203 DEGREES, YOU HAVE FAULTY COOLING FAN,SHORT IN FAN WIRING OR ENGINE COOLANT TEMPERATURE SENSOR FAULTY.IGNITION TIMING WILL CAUSE ENGINE TO OVER HEAT.

It could be that the radiator is blocked,try using a good radiator cleaner & see if that makes any difference.....cheers.