Have been working in the auto service industry for 30 years now. Started career with 15 years experience in a machine shop doing engine rebuilding. Have done everything from small engine repair, to pass/light truck, agricultural/industrial, marine, high performance builds, heavy truck and diesel. Now own and operate an auto repair shop. Hold ASE certifications as Master Auto Tech, Master Med/Hvy Truck Tech, L1 Advanced Driveability, Master Engine Machinist, Parts Specialist, Service Consultant. No documented proof that Pennzoil will case engine damage, but in my earlier years in engine machining/rebuilding, most Pennzoil motors had more than normal sludge accumulation. I don't have a degree in lubricants/engineering/chemistry, or anything like that, so I am only drawing my conclusions on what I have seen. In other words, this is only my opinion. I have been told by others 'more in the know' that Pennzoil uses more parrafin in their base stocks though. (that's wax). This would account for the sludge. I don't know anything about Pennzoil's new formulations, so it is unfair of me to pass judgment on their current products. It is just that when I see a Pennzoil bottle, because of my experience with internal engine work, I just cringe. The new stuff is probably OK, but I am sticking with Mobil-1 in my Viper, Corvette, and Challenger. .........Respectfully, Allan