Coolant on reservior is rising?

Last week I noticed the coolant was way over the max. Coolant was almost topped off of the reservoir almost spilling. I removed the coolant to bring it up to the max. Three days later, I check to see that its going up over the max again. Almost to the top of the reservior. Why is it doing that?

Coolant is still the light color green. Prestone. I did a drain and flush two years ago.

Thanks for the help



Did you check the overflow tank when the engine is hot? If yes, what you noticed is normal. As the coolant in the radiator expands the expanded hot coolant spills over into the overflow tank. When the coolant cools down, it contracts and the “excess” coolant moves back to the rad. If the overflow tank is close to overflowing with coolant, reduce the amount of coolant in the tank once everything has cooled down - not when the engine is still hot as you might take out more than what should be taken off.

Thanks for the response.

But is it normal for the coolant to fill up the whole overflow tank? It was almost spilling out of tank w/ engine hot. Small puddles were seen on the ground. I did some researching from Honda tech, and some say to replace the rad cap. What are your thoughts?

Replacing the cap makes sense. One, the cap helps keep coolant temps down. By keeping the system pressurized, the cap keeps temps down (one of those laws of physics that relate pressure, volume and temp). Secondly, and on a related matter, if the cap can’t hold on to the proper pressure, if the expanding coolant can easily move past the cap then the overflow tank will get a greater than normal amount of overflow.

Yeah, change the cap as a starting point. It’s cheap anyway.

when u change the cap make sure to clean the surface of the radiator neck where the cap seals against. then from that check all ur hoses and lines. if ur radiator hose is pretty soft, u should consider changing them all at once (including small coolant lines around the IM).