A Toyota Prius has joined my shared fleet in what so far is . Since I love knowing all I can about every vehicle in the fleet I’ve been binging all sorts of Prius videos. One of the ones that I’ve come across is a detailed teardown of a high-mileage 2004 Prius engine that looks good, even after some neglect.

A few readers have expressed concerns about picking up a Prius with 90,000 miles and expecting to run it 30,000 miles a year. That kind of driving can be hard on a car. Yet, I’ve seen plenty of second and third-generation Prii driving around in taxi service with more than 300,000 miles and still kicking. If, like me, you wonder what the engine of a high-mileage Prius looks like, tore one down and examined its wear.

The engine here is a 1.5-liter 1NZ-FXE inline-four from a second-generation Prius with 303,561 miles.

This engine uses a low compression ratio and a high expansion ratio. This works by holding the intake valve open longer for a reverse flow of intake air into the intake manifold, . The result is less power but more efficiency, perfect for a hybrid. The 2ZR-FXE uses a similar system.

The YouTuber informs us at the beginning of the video that the engine was running fine without issues before the teardown. The Prius the engine was taken out of was a parts vehicle.

Our host tears through the engine, giving us a thorough explanation of how everything works. But we’re here to see how this engine has fared over 17 years, and the video certainly delivers.

First up is a tour through the positive crankcase ventilation system and even the throttle body, which presents some dirty build-up and could use some good cleaning.

But the valves appear to be clean thanks to the injectors.

Next, we take a peek under the timing chain cover, where things look a little discolored. The YouTuber says that this is likely because the car may have not gotten timely oil changes but even then, there isn’t a lot of wear.

The camshafts and the head also look clean for the mileage they’ve gone through.

Further in the teardown, the YouTuber cracked open the oil pan to reveal a sad sight.

Yep, that’s sludge. They blame the sludge on cheap oil, the cheap oil filter and deferred oil changes.

The filter in the oil pump pickup tube appeared to be pretty gunked up and the pistons have some carbon buildup on them. The bigger point of concern for the YouTuber was clogged-up oil control rings on the pistons.

The host explains that this could mean that the engine might not have been getting proper lubrication there.

Overall, the engine looks pretty good despite some neglect. It’s no wonder why Prii are able to rack up so many miles on their odometers when they appear to be so durable. Still, the sludge build-up is a perfect example of why you should always keep up on your maintenance.