I wouldn't worry. Cars in Australia (I don't know your engine per se) spec 10W-30 for economy but as temps rise, spec 10W-40, 15W-40 and 20W-50 if you like. And this is for current cars, let alone ones from 1994. For example, GM V8s here (eg LS1, L76, LS2) spec 10W-30 but the dealers will put in...