Hey I have a 2002 Honda Civic with a manual transmission. I have had an issue with my coolant overflow tank filling up with coolant and sometimes spitting coolant out of it when it is full. I have replaced the radiator and cap and thought that is was good but now it is still happening again. I have also tested for a blown head gasket with that color changing liquid and it says that it’s not blown. I am unsure of why it is still doing this still. Is it possible that there is air in the system and that’s possibly why it’s pushing coolant into the overflow? Also is it normal for the coolant in the overflow to fluctuate or just stay at the same level all the time? Thanks
Coolant expands and contracts with engine temperature fluctuating. This means that when the car is cold - not driven for an hour or two - level in the expansion tank should not be more than bit above a minimum mark. And when car is hot - just driven for about 1/2 hr or more - level should settle at bit less than maximum level mark.
This means that if your level is close to the maximum mark when car is cold (cooling system overfilled), you will blow coolant out of expansion tank overflow tube while driving
Now, let’s assume your level is correct when car is cold, … but it spills coolant when hot, you most likely have problem with temperature control. Thermostat stuck in a close position and so your engine temperature is rising into overheating zone.
Bottom line: … don’t drive your car, check/thermostat immediately! Remove it, immerse it in the pot full of water, … boil it. Watch it if it opens. At about 180 - 195 deg. F it should be fully open! If not opening, … you need a new thermostat!
F.S.
For the price of a new thermostat and gasket, I would replace it just for the fun of it.
