Never mix ethylene glycol with propylene glycol. Once heated, the mixed antifreezes will gel and burn up the engine. Years ago, a fellow collision tech put the old stuff in a new GM car and our dealership had to pay for a new engine.

As far as the warranty goes, our fellow commenters are correct. You are not required to use the MFG named products. However, you must use coolant with the exact same ASTM number.

This number indicates whether or not the aftermarket product meets or exceeds the MFG recommendations. This is very important because the MFG often requires certain additives be present in the coolant.

These additives are mostly anti-corrosive compounds like nitrites, silicates, phosphates, and borates.

Be rest assured, if the ASTM is the same as the OEM branded product, it will not void any warranties.