losing coolant out of overflow but isn't overheating.

[iwantarolla]

Car - 1991 nissan pulsar Q

motor / part in question - 1.8l sohc

problem - i was driving up the free way the other day and then pulled in to the car park and noticed coolant on the ground. i lifted the bonnet and coolant was bubbling out the coolant overflow like dish washing detergent. as it being a newly bought car i have been checking the temp gauge quite often. it never got to running temp. so i topped it up and bleed the system as best as i could. it didn't do it for a couple of days then it did it again. i have replaced the radiator cap thinking it was screwed. i then toke it for a drive that night and it did it again. i checked the radiator to see if there was still coolant and it was full, the over flow was at the right level but now is almost full. it doesnt seem to be over heating well by the temp gauge. the fan comes on at running temp then temp starts to drop back off. i dont know where to start looking is it a air lock? it doesnt seem to have water in the oil or oil in the coolant.

any help will be great

thanks chris

[matt99]

Possible blockage in the radiator or could be a hammered thermostat maybe?

[iwantarolla]

coolant seems to be flowing through but how would you check pull the hoses of and put a hose in or what?

[Matt]

Thermostat sticking shut can cause this and a blocked radiator / dud water pump etc.

Had it happen on a car of mine years ago, and ended up doing the head gasket to resolve it after replacing radiator, thermostat and water pump.

[trikzlane]

best place is to start simple, replace your radiator cap. then check the thermostat is open when it should

[iwantarolla]

im going to flush the radiator and check the thermostat then go from there thanks guys