HONEST JOHN EXPERT ADVICE

The dealer you can trust is on hand to answer your questions on car problems and consumer issues

FILM NOIR

I will collect my Motability-sourced Mercedes GLA very soon but Motability has said it is prohibited for a dash-cam to be wired to the fusebox, while Halfords said that my device cannot practically be installed by connecting it to the car’s cigarette lighter socket. Any idea how I can incorporate the unit? GM

I don’t know of any dash-cams that can’t be powered from the accessory socket. They can be wired into the car, but if Motability prohibits it on a leased vehicle then that’s the rule.

SPOKES PERSON

Why it is advised not to fit a rear-door bicycle carrier to the Volkswagen T-Roc? The only explanation I can find online is that it is due to the design and/or strength of the tailgate. Dealerships are equally vague and suggest using roof bars or a tow-ball attachment. What is the best method to carry bicycles? RB

I’ve never been keen on bike racks slung on hatchbacks, because some can’t take the weight. The answers are to fit a towbar, then use a Thule bike rack or similar that fits on the towball. Or use roof-mounted bicycle carriers.

PETROL IT IS, THEN

I’m thinking of buying a VW Golf Mk6 to keep for some time as my annual mileage is low. However, I’m not sure whether to go for a 1.4 petrol engine or the 1.6 TDI. I understand that diesel engines last longer, but I’m worried they may be increasingly persecuted by emissions legislation. Is this true? PJ

Diesel engines used to last longer when they were simple, but not any

It’s sensible advice. You don’t want to run a diesel at less than 1,500rpm or it won’t properly regenerate its particulate filter. My Renault Koleos runs at 2,200rpm at 70mph and I never have any DPF problems.

TOO GOOD TO BE TRUE?

I am considering a used Mini Clubman with a petrol engine. While shopping around online, I’ve found Motorpoint prices very competitive

VOLKSWAGEN GULF

I have a VW Golf GTI with a retro-fitted Garmin satnav, which includes a speed icon. This runs consistently 4mph slower than the VW speedo. Which is likely to be the more accurate? CM

The satnav. On a straight, level road with a clear signal path from the satellites, it gives you an extremely accurate reading. Car speedometers always tend to over-read.

Yes. Use any branded super, preferably Shell V-Power, BP Ultimate, Esso Supreme, Total Excellium or similar. On 95 Ron, engines lose a little power and torque. Don’t buy an expensive car then try to save money on fuel. It’s a false economy that might cost you in the long run. Also, don’t pay more than £1.50 a litre for superunleaded.

when compared with conventional car dealers. Why would that be? RR

It is mainly to do with the way they buy cars – sometimes ends of lines, sometimes unsold over-age stock, sometimes minor trim misbuilds, not 100 per cent to UK spec, and sometimes bulk buys, whether new or with low mileage from fleets. Just make sure you ask sensible questions (and beware evasive answers) to ensure you get what you pay for.

THE END GAME

Costco has told me that if I have two new front tyres fitted it will also have to fit new rubber at the rear. Is this a safety issue and, if so, could you explain? AB

It’s Tyre Safety Council advice to help prevent rear tyres losing traction and the car spinning when braking into corners in the wet.

NEUTRAL TERRITORY

I have a 2010 Mercedes E350 estate that has dropped out of gear at low speed three times, in forward as well as reverse. My garage could find no fault. Is it time to get rid, or can it be fixed? ER

It probably needs fresh gearbox fluid. The dealer might tell you that the transmission is “sealed for life” (because he wants to sell you a new gearbox). You need to contact fedauto.co.uk to find a member that has a Liqui Moly Geartronic transmission fluid dialysis machine.

Virtually every new petrol-engined car had to have a petrol particulate filter (PPF) from September 1. They are usually located close to the combustion chambers, are thereby self-cleaning and have far less soot to deal with then the equivalent filter in a diesel engine. I don’t foresee problems, but I’ll wait and see.

CHANGE OF NAME

I have a Toyota Auris 1.8 hybrid on a PCP that ends soon. I am happy with the car, but note it rarely gets a mention in your column and generally gets only semi-positive reviews. Is there something better I should consider instead of buying another Auris? DW

It is regularly mentioned in outgoing emails, but if readers’ questions are too lengthy they aren’t selected for the published column. The Auris is very well built and has proven reliability. It’s also still the only hybrid in its price range, though others are on the way. An all-new Auris hybrid, arriving by the end of the year, is returning to the worldwide model name of Corolla.

SLOW TO ADAPT

We have a VW Golf 2.0 GT TDI 140 manual, registered in January 2009 and with 80,000 miles. It is one of the cars affected by the emissions scandal, but on the advice of a mechanic we did not take up the adaptation offered by VW. It runs very well and economically so we had no intention of changing it until we heard that it might not pass the emissions test of the new MoT. Would using AdBlue help? Or would it be best to sell it while it still has some value? CH

You cannot use AdBlue in a car that does not have a selective catalytic reduction system. Either have the VW NOx update done, because VW has pledged to fix any consequential problems, or try to part-exchange the car. You will get a better resale value after the official NOx update.