Boy I knew were going to get a lot of advice on this. I am using quaker synthetic, but never had a problem with regular quaker. About 20 years+ ago both quaker and pennzoil were streight parifin oils and left a lot of sludge in your engine. I had no problems using quaker for 10 yrs now. My 62 is high reving and uses a 195 thermostat. That is one of the reasons that I started using the synthetic. I use Lucas additive on a regular basis.
