There are supposed to be one or more Toyota engines that are sludge monsters, but Toyota denies it. Some people have claimed that they had major sludge problems with certain Toyota cars and vans, and maybe some trucks and SUVs. I own a Saturn and Saturns may have some sludge problems. Obviously, I cannot prove this. But my car has some sludge even with 3000 mile oil changes. In fact, most of the time I changed oil sooner than 3000 miles-I would change it as soon as I started to get close to 3000 miles. I can think of only one time I exceeded 3000 miles, and that was only a couple of hundred miles. When I used Auto-RX, the oil filter after the first treatment definitely had some sludge in it! I really believe in Auto-RX, and I am very glad that I found this web site. Aside from Auto-RX, I have tried other products that people who come to this web site praise. For example, I used Berryman fuel injector cleaner, and it works! The Chevron fuel injector cleaner I used to use did nothing, as far as I could determine. But as soon as I used the Berryman product, the car performance went up. I am switching to Chevron motor oil and Wix oil filters (NAPA, CarQuest), because of favorable reviews by people at this site. Baldwin air filters are rated highly by some at this site, but I can't get my Baldwin air filters locally anymore. I will have to find another air filter.