Car Clinic

A A product such as Comma’s Diesel D-Tox does what it says on the can. It is designed to remove long-term build-up of carbon deposits and other by-products of the combustion process. But it is better used on older engines and/or when you notice your performance going off or your mpg dipping below the norm. While your low-mileage Picasso is turning in figures like this, it would appear to be in good condition and not ready for a clean-out.

Q I own an S-reg Saab 9-3 convertible. The car is in good condition and I plan to keep it. My problem is that on the soft top, close to the rear window, the canvas is starting to wear. This seems to be due to the mechanism rubbing the canvas when it is raised and lowered. Is something wrong or is it just wear and tear? Would you recommend replacing the hood and do you know of any businesses in the northwest that specialise in replacement hoods? — DC from Manchester

A We spoke to Car Hoods Northern (01925 759 800, www.carhoodsnorthern.co.uk ), who told us this wasn’t a common problem. However, as with all such powered hoods, there’s a welter of electric motors and micro-switches involved in its operation and any one, or more, could be failing or going out of synchronisation and causing the metal frame to rub against the canvas.

The company would be able to confirm this with a simple examination but if work was required it would need to go to a Saab dealer (0845 300 9395, www.saab.co.uk) because only dealers have the computer program necessary to find the problem.

You can expect to pay half an hour’s labour for the diagnostics and a further half hour if it can be corrected on the spot. If this is the case, you might not need a new hood — although given the effects of the hood-unfriendly UK climate and constant attacks from tree sap, bird lime and general airborne detritus, a hood that is eight years old is usually getting pretty tired.

We’d suggest you use Autoglym’s Fabric Hood Cleaner (£19.99 from Halfords, 0845 762 6625, www.halfords.com) to keep it in good condition. This includes both a shampoo and a reproofer (which keeps the water out). If you need a new hood, Car Hoods Northern can supply and fit one for £925. It’s unlikely the headlining (the roof lining) has been damaged, but if so replacing this adds £500 to the price.

Q In September 2004 I bought a new Seat Altea 1.9 TDI Reference for £14,250. It has done 20,000 miles and I am thinking of selling but am alarmed at the depreciation. Given that I would be looking to replace it with a similar car, would I be better off keeping it and if so for how long? — DC from Shropshire

A Depreciation on a new car is heaviest during the first couple of years but starts to ease off after that time so there is some sound logic in hanging on to the car for a little bit longer.

You should be covered by the manufacturer’s warranty until the car is three years old, and will have the option of extending that at the car’s third birthday.

The Seat is by no means the best or worst car in terms of residual values and you may well find that changing the car now and spending another £7,000 on a new vehicle will see you in exactly the same situation in two years’ time.

If the car is causing no problems (and it should still be running well considering its low mileage) then the most economic solution is to keep it for two more years.

If and when you do change your car, shop around for a discount. You should be able to save £1,000-£3,000 off the list price of a new car, depending on the make and model, and this will have the effect of reducing the money you lose in depreciation.

Q I have a three-and-a-half-year- old Ford Galaxy Ghia 1.9 TD. The climate control has failed (apparently bits of metal have got into the condenser) and my dealer has given me a quote of £2,000 for a new system.

Is this reasonable, and could it be done more cheaply if I went to an air-conditioning specialist? Although the car is out of warranty is it worth pursuing Ford for a contribution? — DA from Exeter

A We spoke to an independent specialist, Automotive Cooling Services (01604 639 005, www.automotivecoolingservices.co.uk), who said it is rare for a compressor to fail to the point where metal bits break off — it usually tends simply to stop.

In such a case it would be more usual to replace the compressor and condenser, the rest requiring only a careful flush-through. The quote you have seems to be for replacing absolutely everything.

It’s definitely worth getting a second opinion if you’re paying the bill yourself. However, before that we’d suggest you contact Ford directly, because it has a good reputation for looking favourably on such problems, especially when the projected bill is so large and it’s so near the end of the warranty period.

Call the “customer relationship centre” on 0845 841 1111 and tell them the problem.

Each case is judged on its merits, against such factors as the overall condition of the vehicle and whether it has been properly and regularly serviced.

Q I have owned and loved my 1974 Mercedes SLC 450 for many years. Its only fault is that the wiper blades, when activated, only clear half of the windscreen, which makes it impossible to drive in the rain.

I’ve been told the whole dash will have to be removed and new linkage arms fitted. The cost of this work is estimated at £600-£700 plus Vat.

Is there an alternative? It would break my heart to have to take it to the scrapyard as the car is in otherwise immaculate condition — RW from Ickenham, west London

A The SLC 450 is a beautiful car and made back in the days when Mercedes’ build quality was the envy of the world.

We spoke to Reg Burrows at the Mercedes-Benz Classic Cars Workshop in Shepperton, southwest London (01932 782 885) who reckons there’s more than a fighting chance you might not have to go to these extremes.

The mechanisms often seize through lack of use, but with the wiper motor removed — a relatively simple task — it’s possible to get to the problem areas and apply penetrating oil. Left to soak, this often solves the problem without the need for complex surgery or expensive spare parts. If you’re not able to do this yourself, Burrows’s workshop can do it in about two hours at a cost of about £70.

We’d definitely advise against the scrapyard. If it is immaculate, it could be worth considerably more than you think. Because of its classic status and undeniable panache, a good one should make upwards of £2,500 privately. More important, it’s almost certain to become an even better investment in a few years’ time as it will become rarer and more sought after.

Q I have a Vauxhall Astra Coupé Bertone 2.2 litre automatic with cruise control. It is 15 months old and has only done 2,500 miles. There is nothing wrong with it but I’ve decided it’s not suitable for my advancing years. What do you think I might get for it? — JB from Loughborough

A It sounds as if your Astra was one of the last of that model to be registered in the UK. Assuming it is a 2005 55-reg car we would estimate that a dealer would offer you between £8,500 and £9,000, although they may give slightly more if you part-exchange it for a new car. This is likely to be about half the price you paid for the car just a short time ago but unfortunately the heaviest depreciation occurs in the first year or so of ownership. The fact that the car has ultra low mileage will help a bit but you still need to be prepared to suffer a relatively heavy loss.

E-mail your questions for our experts to carclinic@sunday-times.co.uk or write to Car Clinic, Driving, The Sunday Times, 1 Pennington Street, London E98 1ST. Please give a daytime telephone number. We cannot send personal replies or deal with every letter. Please do not send original documents or SAEs. Advice is offered without legal responsibility.