Are you sure they aren't already clearcoated? OEM wheels normally are.
Some aftermarket polished wheels aren't.

A polyurethane liquid clearcoat won't adhere well to polished aluminum. You
would want to get a powder coat finish, preferably acrylic although
a polyester will do as well.

Another option, especially if your wheels won't be exposed to salt
is Zoop seal. Zoop seals the surface providing less chance of corrosion.
If the wheel isn't exposed to harsh conditions, it should keep the finish
looking good for a year or so.

Dan
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