Its a recurring theme over the last decade. In summary its a combination of design and neglect. Will explain. Neglect any engine it will eventually die sooner or later one way or another. For GM's it may be mechanical malfunction, bearings, throw a rod, etc. For Toyota's its sludge. Toyotas engine design includes the use of lightweight aluminum for the block and head. While this helps lighten the car and increase economy, the aluminum used is not very efficient dissipating heat. Hot spots, moisture. Neglect the oil, dont change it, use the cheap stuff, you end up with old oil thats lost its add pack and fries on the engine surface while cool in other areas. Moisture + fried oil = sludge over thousands of neglected miles. The fix? Maintain the engine properly and stop procrastinating. If you hate maintaining cars use more expensive synthetic oil. Bad maintainers are generally cheapskates so they use the cheap stuff, then google for Toyota sludge and post blaming Toyota. "I changed my oil right on time and Toyota won't fix my car". Neither would I because your obviously lying, and your maintenance practices caught up with you. And being a cheapskate you want somebody else to fix your problem. "I bought a Toyota because they are supposed to be reliable, and they are not!!!". Uhh.. that doesn't mean you don't have to maintain it. That's my opinion on 90% of the complaints. Anyways to deal with this Toyota chose thin better flowing synthetics for 2011+. Makes sense. I agree, I'm using synthetics too.