the protective coating be fully repaintable with other primers and topcoats so that the two coat weldable primer system of this invention can provide the preprimed surface required by the automotive industry among the resins which are useful as binders in the protective coating compositions are cross linkable linear polyesters of aromatic dicarboxylic acids and alkylene glycols cycloaliphatic dicarboxylic acids and dihydric alcohols are also suitable reactants in the preparation of the polyesters the polyesters may also be derived from mixtures of aromatic dicarbocylic acids some of which are symmetrical one or more acyclic dicarboxylic acids one or more cycloaliphatic dicarboxylic acids and one or more of the diols examples of the symmetrical aromatic acids include terephthalic acid bibenzoic acid ethylene bis p oxy benzoic acid and 2 6 naphthalic acid unsymmetrical aromatic dicarboxylic acids which may be used along with the symmetrical ones are exemplified by o phthalic and isophthalic acid hexahydrophthalic acid and alkyl hexahydrophthalic acid and their anhydrides wherein an alkyl group having up to about seven carbon atoms is bound to the cycloaliphatic ring are examples of the cycloaliphatic acids contemplated along with 1 4 cyclohexanedicarboxylic acid the dihydric alcohols are represented by ethylene glycol 1 2 and 1 3 propanediol neopentyl glycol 1 6 hexanediol 1 4 cyclohexanedimethanol and the like examples of the acyclic dicarboxylic acids which may be incorporated into the polyesters along with the aromatic and cycloaliphatic acids include adipic acid pimelic acid suberic acid sebacic acid azelaic acid dodecane dioic acid and the like in a preferred embodiment the polyester is derived from a mixture of aromatic.