heavy oil will help the last thing you want to do is clean out an old engine.i remember driving a 59 ford with a 361 edsel motor i stopped for gas and asked for a can of stp which i used in those days and i let the guy talk me into putting something in that was the latest.would make my engine run great and clean it.when i pulled in for gas 200 miles down the road on came the oil light it was down 2 quarts.never got over 200 miles to quart again.