Q: My radiator seems to forcing coolant into the reservoir.

Hi there:

If your engine is not overheating or showing any signs of cooling system problems, then there are two reasons why additional fluid will show up in the overflow reservoir. First, it’s possible you might have too much coolant inside the cooling system. The second possible reason for this to occur is if the coolant mixture is too thick. As coolant gets hot, it expands; which is why manufacturers recommend a 50 / 50 ratio of coolant to water; so that it doesn’t overflow into the reservoir as often. You might want to flush your radiator and fill it with a 50/50 coolant blend first to see if this solves your issues.

This is proper operation of the coolant reservoir. It is also known as the expansion tank. As the coolant is warmed by the motor operation, it expands. If there wasn’t some relief in the system, hoses and other parts would eventually burst.

There is an exception to this. If the coolant reservoir has been properly filled to its full mark when the motor is cold, it should not overflow. If it does, then your motor is experiencing an overheating conditions of some sort. There are conditions that can cause the coolant reservoir to over fill but the motor won’t show any obvious signs of overheating to the driver. If this condition exists, it will need to be investigate further. It isn’t an easy thing to make a determination for.

If you still feel you have a problem, I recommend the following inspection to help you out. Car is overheating I chose overheating because a over flowing expansion tank is a precursor to a larger cooling system problem.

Good luck!