Coolant seems to be disappearing

[Prow Ginger]

I recently had the heater hoses replaced and the coolant flushed on my '94 Explorer Sport 4x4. When I checked the coolant this morning it seemed to be pretty low. There wasn't any in the expansion tank and when I opened the radiator I couldn't see any coolant in there either. I filled the reservoir to the cold fill line and took it for a drive. I didn't notice any leaks and the temp was fine. Should I be concerned? Is this normal?

 

[Rick]

There was so much road debris at the base of my radiator that the water that was seeping out was getting absorbed in the mess... Turned out the plastic side tank had a slight leak.

Another potential leak is where the intake manifold meets the heads. The water passage can get corroded to the point that it leaks.