It's a waste of money, if you use Syn oil just use 1 qt with your normal oil, say 4 qts of penn and 1 qt of penn syn, or mobil drive clean and mobil syn. Putting all syn oil doesn't do anymore for your engine than just 1 qt in with your normal oil. Or just add a bottle of duralube or slick 50 in with your normal oil, because all syn oil is is just normal oil with a treatment in it, like duralube or slick 50. Just my 7 cents
