On Wednesday, 29 July 2020 08:17:13 UTC+1, alan_m wrote:
On 28/07/2020 14:31, Chris Hogg wrote:


Isn't that advice just so that rain will wet the windscreen and allow
wipers to sweep it away smoothly, leaving a continuous film of water,
rather than the windscreen being water-repellant and always looking
greasy in wet weather, and perhaps interfering with the driver's
vision? I doubt if it matters with a sun roof.


+1
On the occasional use of a spinning brush car wash, with all the
trimmings, I find that afterwards the windscreen has to be cleared of
the wax with a good scrub of detergent. I find the problem with a waxed
windscreen is in very light rain when using the wipers in single sweep
intermittent mode. The windscreen never appears completely clear.

That is one of the reasons I have seen quoted. Especially if used generously.

It also reported to affect wiper blades.