Q: Coolant issue - 2008 Honda Accord

Hello. When a car is low on coolant, even if you refill both the radiator and the reservoir, air can still be trapped in the system. After you run the car for a while, the trapped air is expelled and then the resulting "vacuum" causes coolant to be drawn from the recovery reservoir back into the radiator.

That might make it appear as if you are loosing coolant or have a reservoir leak, when in fact all that is happening is the system is just normalizing itself. So the reservoir might not have been leaking in the first instance. At this point, if the level of coolant is still falling in the reservoir top off the coolant as this occurs over several days.

At the end of that period, the level in the reservoir should remain steady (you have to judge the level when the car is either hot or cold; the level will vary significantly depending on temperature, so always check cold, first thing in the morning to be able to really accurately judge what is going on with the level in the reservoir).

The point is after a week of "topping off" and/or monitoring the reservoir level, if the level does not stabilize, then you have a leak. Coolant leaks are of two types: external and internal. External leaks are no problem and YourMechanic can identify those via simple pressure testing. Internal leaks through a head gasket are a mini nightmare though. Hopefully, your past overheating experience did not damage the head gasket on the engine, causing an internal coolant leak. If so, the head has to be removed from the engine, checked to make sure neither it nor the block are warped and a new gasket carefully applied in the auto mechanic’s version of "clean room" conditions. If you cannot get the coolant level to stabilize, YourMechanic will find the leak for you and then explain the least costly and most efficient options to get it resolved.