Where is my coolant going?

[WeiLi...@taiwan.com]

I have a 2001 S10. For a few years now, it has been losing coolant. I
just added a full gallon to the overflow container. I have done that
before, maybe three times now.

I see no evidence of leakage under the truck. Performance seems just
fine. I am wondering....could I have head gasket leakage? Should I
fix it? The truck has 90K miles on it, and has had zero repairs. Uses
no oil.

Thanks

Wei