Q. My new diesel Vauxhall Astra is the first hatchback I have owned and I can’t believe how dirty it gets at the back — even assiduous use of the rear wiper does not shift the oily diesel deposits from the screen. How can I counter this problem? Perhaps one of those slatted plastic covers for the rear screen, as favoured by boy racers?
A. The aerodynamics of a hatchback are different from those of a saloon because the abrupt cut-off at the back causes air passing over the vehicle to swirl around the rear of the car, creating a vortex that sucks airborne contaminants, including some of your own exhaust fumes, back towards the tailgate and rear screen.
Some cars suffer more than others — second-generation Volkswagen Golfs, for example, were renowned for it. (With a saloon, air tends to pass over the vehicle and flow away in a “teardrop” shape, which is why these cars rarely need a rear wiper.)
However, a good-quality screenwash added to the wiper reservoir should be able to cut through oily residues on the go. Try Comma Xstream screenwash concentrate (£1.50 for 250ml, demonoils.co.uk).
For driveway glass-cleaning try Black Diamond Quick Glass (£3.99 for 500ml,blackdiamondproducts.co.uk). Remember to wipe down the rear numberplate too: if it’s unreadable you could receive a £60 fine.
The slatted plastic covers you refer to are known as rear-screen louvres. Their only real practical benefit is to inhibit the effect of strong sunlight on the interior, and they certainly don’t improve visibility. We wouldn’t advise investing in them.
Dave Pollard has written several Haynes manuals and has tested just about every car-related accessory
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