You can use Berryman B-12 Chemtool Fuel Treatment (part #0116) in the crankcase immediately before an oil change. It is extremely effective in the removal of gum, sludge, and other deposits. However, there is a caveat. If sludge or carbon build-up on worn oil rings has been helping to seal the crankcase, applying B-12 could actually cause the engine to begin smoking even if it didn’t before. This is an uncommon occurrence, especially with well-maintained vehicles and those with lower mileage, but please be aware of the possibility. If you would like to use B-12 as an engine flush, pour into your cold crankcase approximately 1½-2 oz. of #0116 per quart of oil capacity. For instance, if your vehicle holds 5 quarts of oil, then you would use 7.5-10 oz. of or about half to two-thirds of one can. After you’ve added it to your cold oil, start the car and run it at idle 10-15 minutes until the oil is warmed up. Then change the spent oil and replace the oil filter.