Whatever you use, make sure it is labeled as being safe for aluminum and personally I would only use something made for motorcycles. You only change every year or two so why be cheap? Also distilled water only, as mentioned above. Coolant contains anti-corosives that will work best if mixed according to directions (usually 50/50). Also, you want to have the proper antifreeze protection which is achieved by mixing to the proper proportions. I don't believe you should vary too much from the directions on mixing.