And yes, diamond cut has been a problem on or after 3 years on both of my Mk7.x's. It is a liability and VW should be utterly aware of this. They don't make body panels that rust after 3 years, why make wheels that fall apart after 3?
It's not just diamond cut wheels that have this problem. My Mk5 had plain silver wheels, 3 of which got replaced under warranty for peeling lacquer just before the 3 year point. The fourth wheel also started to peel not long after the warranty expired.
My Mk7.5 has just turned 3, and so far the diamond cut finish is holding up pretty well. 🤷♂️
I’ve never had an issue with painted / powder coated alloys, and all but one of the cars I’ve owned since 1982 have had alloy wheels. The only alloys I’ve had an issue with have been diamond cut.
The finish on diamond cut alloys - a ‘protective’ coat of lacquer applied to a bare, machined / polished surface - doesn’t result in a particularly durable finish, as the bare metal surface doesn’t provide a good ‘key’ for the lacquer to bond to. Additionally, the thickness of the lacquer may be less on the edges of the spokes and other parts of the wheel where there are ‘sharp’ edges and changes in the angle of the metal face on the wheel, so potentially more limited protection in these areas. A small stone chip left unrepaired on the edge of a spoke, and water can get under the lacquer and you’ve got the ideal conditions for the start of white worm corrosion.
As Fred has said, there can be issues with white worm corrosion at around three years, and based on many owners experiences on various forums I visit, it’s pretty commonplace. I’ve read of very few instances of corrosion issues on painted / powder coated alloys. There’s a good reason why many reputable alloy wheel refurbishing companies provide a more limited warranty on diamond cut wheel refurbishments than the warranty they give do on painted / powder coated wheels. It’s also not unusual for aftermarket alloy wheel retailers to not recommend diamond cut alloys for winter use.
I had two diamond wheels succumb to white worm corrosion when they were at 2.5 years old. I’m pretty OCD about my car, and the wheels were cleaned every 7-10 days, protected with wax and / or sealant every three months, and any stone chips repaired pretty much as soon as they occurred. In spite of this, two wheels suffered from white worm.
Given the choice, I’d go for alloy wheels with a painted / powder coated finish every time.
Apologies if I’ve taken this thread off topic, but the diamond cut finish on the standard 18” GTi alloys is one of the reasons for hating / disliking those wheels - or any diamond cut wheels for that matter - so IMO the above is relevant.
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