Okay Corey, here is the answer (or not) straight from Sonax customer care.
Hi Jon-
Thanks for contacting us and I hope you’re having a good week.
Regarding your question about the SONAX Wheel Cleaner being safe for the plastic center cap on a vehicle.
The short answer is, I really don’t know. It depends on what the center cap is made of (i.e. different materials that are used in processing plastics) and what kind of coating or treatment the plastic part has had.
I will tell you things I do know.
1. The SONAX Wheel Cleaner is 100% Acid free and ph-neutral. It will not harm or damage any type of wheel that is out on the market now and that includes not destroying the clear coat that is applied to almost every wheel now. SONAX Germany has explained to us the product is all surface safe.
2. Per your specific question, I have not seen or been provided with any feedback from anyone that has used it in which they’ve had a problem with the Wheel Cleaner discoloring or destroying a plastic wheel cover.
Sorry if I didn’t specifically answer your question. I just cannot 100% guarantee it will not discolor the wheel covers.
Please respond to this email if you have any more questions.
All the best, Jason
Jason Whiteley
O: 317-295-7056
C: 317-430-9809
SONAX