hi ive got a 1994 honda civic EG. the car has half a tank of water/antifreeze in the tank left of the raditator but when i drive the car for over 10 mins i check the tank again and it is almost full to the top. then after leaving it for a few hours it goes back down again.

any reasons for this .thanks

 

its normal, when the car warms up the coolant expands and overflows into the overflow tank, when the car cools down, the coolant gets sucked back into the system

 

there is also the posibility that that your radiator has a crack in it that would not allow the suction of the fluid in the over flow bottle to be sucked back into the radiator due to the fact that the suction that is in the radiator would be sucking air in coz there would be less resistance than pulling the coolant back through the hose.

but, in the sutuation that i've just suggested, the overflow bottle usually gets full & doesn't go back down to half level.. it would stay at the full point.

 

I agree with Running925. You might want to get the cooling system checked(hoses, radiator, radiator cap). Sounds like you have a small leak, and coolant from the expansion tank is being sucked up when the system goes low on coolant. Or there could be no leaks and air already present in the cooling system. When was the last time the cooling system serviced?

 

should be fine as long as the coolant goes back into the system over night and full again when at operating temps. id only be worried if the tank was still full over night or empty when running at operating temps.

 

The overflow tank must have coolant in it at all times. If this is not the case, then there is a cooling system problem.

 

yes, at the min level when left over night. but what hes describing is normal

 

their is nothing wrong

 

He is said that the tank is "full to the top." I read that as sayin that the tank full to the top, not to the max line. If thats the case, I would assume that there is a problem.

 

yeah i can see what you mean, but there could just be extra in the overflow and that would cause it to top out.