There are a few reasons that you could have an empty radiator but a full reservoir.

The most common reason is that the car is parked on an incline. If you park your car on an incline and the radiator is lower than the reservoir, then the coolant will drain out of the radiator and into the reservoir.

A second possible reason for this issue is a leaking hose. If you have a leak in one of your hoses, then coolant will be continually leaking out of it and into your reservoir. This can happen over time or all at once depending on how bad the leak is and how much pressure it builds up behind it before bursting through.

Another possible cause is the overflow tank being overfilled with coolant during maintenance or repair work. The overflow tank should be filled until it just starts to overflow on its own when tipped upside down; if you top off too much, then excess pressure can build up behind any leaks in your system until they burst through and cause problems like this one!

Last modified: November 7, 2022