When I was working on boats, Mastercraft and some other brands, along with a company called Indmar, had developed a relationship with Pennzoil. The place where we were trained is owned by someone who has PE after his name, which means 'Professional Engineer'- this is the top level of licensure for engineering and it also means they have mastery of most engineering disciplines. His shop had three dynamometer rooms, one with a 600HP electric motor, which was used for finding frictional losses in engine builds. During our training, we discussed lubrication and the use of Pennzoil- some mentioned that it caused problems but he had not seen them in his testing or the many years of servicing engines that were in marine or road use. He also told us about people who would occasionally show up to talk about some kind of oil additive- he would aske them to leave some, so he could test it and after he explained how he's able to do that, he never saw them again. He said that, unless an engine isn't operated in extreme conditions, 'oil is oil' as long as it meets the specs for grade, viscosity, etc.
Do an online search using 'Pennzoil causes problems in engines' as the search terms and it's all forums, YouTube videos and opinions, for or against.
I know several people who worked for GM in powertrain development- their advice had little to do with the brand of oil although a couple do like Mobil 1. They all had simple recommendations- keep the oil clean, don't overheat the engine.
I don't change vehicles the way some people change their underwear (every one to three years, whether they need to, or not)- I buy the type of vehicle that will serve me best & keep it until it has served its usefulness, which means the mileage will be high when I move on to the next. I have had zero problems with oil of any brand, I have used Pennzoil and I have seen absolutely no sludge or heavy deposits in any of my engines, other than my first car which was a '67 Ford LTD which hadn't been maintained well. The last five cars had 200K, 194K, 197K, ~300K and >240K, in chronological order. The first was a cast iron 3.8L V6 and was rebuilt because those had severe problems with cylinder taper. The rest needed nothing more than general maintenance and in the case of the one with ~300K, it needed oil seals in the heads. When the valve covers were removed, we saw that they were almost pristine. None of the others had any sludge or buildup of anything on/around the valve stems and rocker arms.
If possible, I'll contact the facility where I was trained, to get additional info about Pennzoil issues.
