B-12 Chemtool Fuel System Cleaner (part #0116) is extremely effective in the removal of gum, sludge, and other crankcase deposits, but it should only be applied immediately before an oil and filter change due to the potential overloading of the oil with dissolved sludge and deposits. Please note that if sludge or carbon buildup on worn oil rings has been helping to seal the crankcase, then applying B-12 Chemtool could actually cause the engine to begin smoking even if it didn’t before. Removal of varnish and carbon buildup can also affect tolerances in old, dirty engines and cause engine noise (clattering). These are very uncommon occurrences, but please be aware of the possibilities. If you would like to use B-12 Chemtool as an engine flush, pour into your cold crankcase approximately 1½-2 oz of B-12 Chemtool per quart of oil capacity. For instance, if your truck holds 5 quarts of oil, then you should use 7½-10 oz. of B-12 Chemtool. After you’ve added it to your cold engine oil, start the truck and run it at idle 10-15 minutes or until the oil is warm. (You do not need to put 50 miles on it or even drive it for that matter.) Then change the spent oil and replace the oil filter.