Some engines have better reputations than others. The 2.5-liter inline-five from Volkswagen is one of the better ones. The engine featured in this recent I Do Cars teardown video came from a 2011 VW Jetta, though the mileage is unknown. What is known is that this mill was deemed too wrecked to be rebuilt.
Not knowing mileage is certainly a bummer, but the investigation into this engine's demise is further complicated by an array of missing parts. Items like the intake manifold and spark plugs are long gone, and this engine sat outside after being pulled. That allowed water to enter places it shouldn't be, and that makes it difficult to suss out potential trouble spots. At first, anyway.
The head looks good if neglected. The cam caps and lobes show minimal wear, but heavy varnish suggests oil changes weren't very common. The timing chain was also compromised with broken guides, possibly pointing to a timing failure. With the 2.5-liter being an interference engine, any failure with the timing chain can cause the pistons to smack the valves. That would certainly constitute a catastrophic failure, and once the head comes off, there's more evidence to support the theory. Two pistons show evidence of hitting the head, and one has a considerable amount of play despite being at the top of the cylinder.
Once the oil pan comes off, however, everything changes. We see two spun rod bearings, and from the looks of it, the engine wasn't shut off when the knocking started. Aluminum debris contaminated the oil, and at some point, the piston with all the play got hot enough to melt on one side. Yikes.
The prevailing theory is that the engine was starved for oil. Whether that means it ran low or just lost viscosity—it's unclear. Another theory is that the engine overheated, causing severe damage to the cylinder, which then led to the bearings spinning.
In either case, it all comes down to basic preventative maintenance. Check your oil, make sure the coolant is full, and if you hear funny noises, shut it down. This engine may have been okay if turned off at the first sign of trouble. Now, it's a thoroughly destroyed mess with little to no usable parts.
Source: I Do Cars / YouTube
