Q My wife has a 2 litre Mitsubishi Shogun Pinin from 2002 that has covered only 20,000 miles. Nevertheless, the fuel economy has dropped from 30mpg to 26mpg. Should we have the car serviced to get the jets cleaned? Is it advantageous to use 98 octane petrol rather than 95?

LW from Langdon Hills, Essex

A First, check your arithmetic by doing a manual check of the car’s fuel economy. Fill the petrol tank, drive for a couple of hundred miles and then refill. Note the number of litres it took to refill the tank and divide this figure by 4.54 to give gallons. Then divide the miles you have covered by the number of gallons used. Do this twice. If you still think the car’s economy has worsened, have its emissions checked to reveal any problems with the fuel-delivery system (injectors) or combustion (plugs). If so, a fuel additive such as Redex or Roil fuel system treatment may help. However, with many low-mileage cars, a decent high-speed run will do just as much good. Most fuel companies now sell “super fuels” and they suggest that these increase power and maintain a cleaner engine. As virtually no modern engines require 98 octane fuel (instead of the more standard 95), much of this perceived benefit is a placebo effect. Little independent evidence exists either way.

Q My fiancée and I want to trade in our cars for another one. Mine is a 2001 Renault Twingo while hers is a 2003 Alfa Romeo 147. We’d like something 1.4 litre and stylish but are open-minded. We could contribute £1,000 to the pot.

KB from St Margarets, Twickenham

A Making some assumptions about your cars’ mileage and condition we think they will be worth about £2,000 and £4,000 respectively, giving a budget of about £7,000 including the extra cash. This will buy you a 2003-4 Mini Cooper, which is stylish and great fun to drive. Another option is the Renault Clio 172. A 30,000-mile model from 2003 is within your budget. This is a high-performance hatchback that came with great specifications as standard, including xenon headlights and climate control.

Q My wife had a “parking incident” that left minor scrapes on the paint of the bumper of our three-year-old Peugeot, which has black metallic paint. As we have a protected no-claims discount – with £150 excess – we may have this fixed under insurance. Is it worth doing so and will the newly resprayed panels look different from the older paintwork?

AP from west London

A It’s notoriously difficult to return metallic paintwork to its preaccident standard without respraying the whole panel. On older cars, uneven fading can also prove problematic. That shouldn’t affect you, though, and most reputable bodyshops will match the colour without difficulty. Your protected no-claims discount means you shouldn’t suffer at policy-renewal time, though you must pay the £150 excess. If the damage is slight, a cheaper option is a Halfords Paint Pen Kit (£10.50 from www.halfords.com). These touch-up kits come in a huge range of colours, each including a brush for cleaning the damaged area, a primer, touch-up paint and a clear lacquer, and can give a pretty decent result. The third way here is a “smart repair” to the bumper. This is localised patch repair that doesn’t involve repainting the entire panel. Smart repairs can be performed by many third-party providers or Peugeot, which charges about £100 per small scrape. Again, it won’t look perfect, but it could well prove to be an ideal middle ground.

Q I’m a taxi driver and am planning to change my car. Most of my jobs are around town, with the occasional airport run. I’m considering a new Ford Focus 1.8 Zetec or maybe a Mercedes A-class – possibly a diesel.

SC from Stamford, Lincolnshire

A The on-the-road price of a five-door Ford Focus 1.8 TDCi Zetec is £17,345. However, good discounts are available on new and preregistered examples. You can negotiate about £2,000 off if you shop around. Buying a “preregistered” car (which will have a few hundred miles on the clock) could save you close to £4,000.

The price of a Mercedes A 160 CDI Classic SE is £15,145 but you are unlikely to get such a large discount. That’s partly because the Mercedes is likely to have a stronger residual value than a Focus when you sell the car. The big problem for you is that an A-class is a compact choice of vehicle for a taxi – you won’t be able to cram much luggage into the boot on an airport run, for example.Also worth considering is theHyundai i30, which is similar insize to the Focus. The car comes with a five-yearunlimited-mileage warrantyand at £14,155 for a 1.6 litre diesel Comfort model, it’s excellent value. As a final alternative, the Honda Civic has a great reliability record. The new 1.4 i-DSI petrol model offers the potential of a frugal 47.9mpg in mixed motoring conditions and costs £14,490.