The rear windows in our 2008 Volkswagen Golf TDI often mist up while driving in cold weather. They can also take several minutes to clear when first starting up in the morning. Why is this?
RJ, Basingstoke, Hampshire
It is likely that water is getting into the car. In the warmth of the cabin, it evaporates and then collects as condensation on the cold window glass. Find the leak and your windows will become mist-free once more.
First, look for signs of damp on the boot floor carpet and under it in the spare wheel well. Beneath the wheel there’s usually a drain hole covered by a rubber plug: make sure it’s properly in place to stop water getting in.
Next, pull back the carpeted side panels in the boot. If there’s damp behind one of them, it suggests a leaking rear-lamp cluster. Remove the cluster — it’s held in by two 10mm nuts, which you can access from inside the boot — and check to see if the rubber seal around the edges is in good condition and not bent out of shape.
Another possible source of leaks is the rear screen. Sit in the loading bay while a friend hoses water around its edges and you’ll soon spot any ingress. Use the same procedure to check the tailgate seal.
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Leaky seals can often be plugged by judicious use of Granville Clear Silicone Sealant (£4.99 for a 40g tube from halfords.com). A leak in the tailgate, however, might require complete replacement of the seal — but not before you give it a really good clean with a specific vinyl cleaner such as Autoglym Vinyl & Rubber Care (£7.49 for 500ml at halfords.com), which can often soften up the seal enough to restore a good fit. DP
My garage tells me I should use my 14-year-old Ford Focus’s air-conditioning regularly in order to keep it functioning. I rarely turn it on as I’ve been told it wrecks fuel economy, but the garage insists that it doesn’t use much more fuel. Who’s right?
PD, Hornchurch, London
Your garage is correct. Air- conditioning “wasting” fuel is a popular topic for the kind of people who like to badger you about the irresponsibility of using a car at all when you could be standing in the rain waiting for a bus.
As with any machinery, an air-con that is left unused for months on end risks having components seize up, so run it regularly during the winter: the circulating coolant fluid will help keep the moving parts lubricated and the seals intact. Since at this time of year the car will already be cool, you will not need to do much more than move the fluid round the system.
Air-conditioning relies on a compressor driven by the engine, and the radiator fan and heater blower will run continuously while it is turned on, so it will burn some extra fuel. But as 10 minutes’ use every few weeks is all that’s needed in cold weather the cost is negligible.
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Obviously it takes more energy to run the air-con in warmer weather when use of the system can make a dent in fuel consumption if you’re doing lots of short trips. On long journeys, though, the difference will be hardly noticeable (because once the car is cool, keeping it that way burns much less fuel).
And let’s face it, even a 10% penalty is hardly wrecking the car’s fuel economy — an efficient driving style and keeping the tyres properly inflated will easily save more than this.
A good tip, come the hot weather, is to drive with the windows down for a few minutes to clear the hot air from the cabin, then close them and turn on the air-con. TS