Mechanic Tears Down 300,000-Mile Toyota Prius Engine, Carbon Buildup Galore

Sourced from a Canadian-spec 2004 model, the Atkinson-cycle lump in the featured video has been torn apart with 488,535 kilometers (303,562 miles) on the clock. YouTube mechanic “speedkar99” says there were no issues with the 1.5-liter engine prior to the teardown, but as it’s often the case with old cars driven in cold climates, the inside tells a very different story.

The spark plugs, for example, feature a little white ash, which is a sign of alloying constituents from the oil. After taking the valve cover off, we can see minor wear that seems normal for such a high-mileage motor. There is, however, crust inside the PCV system and the throttle body is dirty.

Moving on to the back of the intake, the carbon buildup is – dare I say it – atrocious even though we’re dealing with a port-injected engine instead of direct injection. Carbon buildup is also present on the top of the pistons and intake valves, and the 1NZ-FXE exhibits crust on the intake runners.

The oil rings of the pistons are clogged up, which is why the control rings couldn’t wick any oil back inside the pistons. The oil pickup tube is almost clogged up, and the steel oil pan that complements the open-deck block is full of sludge on the bottom. In other words, overextended oil changes are to blame for the state of the four-cylinder motor in this 2004 Toyota Prius.

Cheap oil and cheap filters also take their toll on any engine out there, and lest we forget, extended part-load operation makes things worse very fast.

While there is no evidence of mechanical wear just due to high mileage, the lesson learned here would be to take care of your car’s lubrication system.