Ok, from experience I know Synthetics do and excellent job of cleaning engines. In 90s bought a 79 Jeep with sludged 258 I6 engine. Installed a Oberg racing filter with removable cleanable mesh filter(why because) that lit a light on Dash when Bypass opened. Put Mobil 1 5W30 in, first day bypass light came on. Cleaned filter, Second day filter light comes on, clean filter. 4th day light comes on, clean filter etc. After that time to bypass filter light coming on doubled. Took a month and half before bypass light stopped coming on. Changed oil with more Mobile 1. Light never came on again. After taking off valve cover to check valve lash, it was amazing how clean the engine was, still varnish but nothing like the caked on stuff before. It takes time but synthetic oil works