Like most of the dim-witted yokels on Yahoo! Answers, you FAIL to state the YEAR, MAKE, MODEL, or ENGINE your vehicle has, so no one can say if your rather ill-informed decision was correct or not.

However, GL-5 is a rating for GEAR OIL, typically rear differential oil. I think you may be attempting to refer to G-05, which is a type of antifreeze Mercedes-Benz used years ago. (Some Chryslers and Fords still use it.)

Any coolant that can claim H.O.A.T is sufficient for a mercedes.

Ask at NAPA.

However we have no idea what you are working on.

If it came with Dexcool, There is likely a service bulletin.

Ask the GM dealer.

Whatever "car" you have should not need 3 gallons. so thats another problem.

Ask NAPA to help you figure this out, bring the car and the receipts so far.

Your car will not become a mercedes.

GL-5 was gear lube. when stated the way you wrote

H.O.A.T. means hybrid organic additive technology, for those of you taking notes.

Zerex GL-5 would have been a better choice. It's made to replace Ford and Chrysler brand antifreeze

GL-5 is gear oil like for a rear diff. or a manual trans.