Car clinic: Expanding oil and the puzzle of the missing automatic door locks

Driving's experts offer readers advice on a range of car-related probelms

Checking oil resized

The car clinic experts

Tim Shallcross used to train AA patrols to fix cars. Now he advises the Institute of Advanced Motorists.

Emma Smith is a journalist specialising in consumer issues and is a regular Driving contributor


Q. My Mercedes S 320 has an oil sensor rather than a dipstick, and has recently started displaying the message “reduce oil level” on the dashboard. This occurs after about 20 minutes of driving. When I do an electronic oil-check, though, it tells me the level is OK. Given that the last oil change was more than 4,000 miles ago and no oil has been added, why is this message appearing? 

AO, Farnham

A. There are two questions to answer here. First, why does the “reduce oil level” message come on only when the engine is hot; second, why is it happening long after a service and when no oil has been added?

Oil expands slightly as it heats up, and by the time your engine is at operating temperature, the volume of oil has typically increased by a quarter of a litre. This is not usually noticeable on the dipstick but the electronic oil-level sensor is more sensitive, which is why the oil level is too high after 20 minutes of driving, but OK if you check it when the engine is cold. Some owners keep the level slightly below maximum for this reason.

You would expect the oil level to slowly reduce over time. One reason why yours appears not to be doing so could be because water in the air is condensing on cold engine internals and draining into the oil sump, adding to the oil volume. The volume could also be increased by unburnt fuel leaking past the pistons of a cold engine.

On short, low-speed trips the engine oil doesn’t get hot enough to evaporate these unwanted liquids, so if a car does only short journeys the oil level may steadily rise. Try taking the car on a long run (100 miles, say) to get the oil hot enough to evaporate the contaminants. This should lower the level, possibly by enough for it to need a top-up.



Q. My three previous cars, all Peugeots, had a system that allowed me to set the doors to lock automatically as I drove off. I found this reassuring when driving in cities, particularly at night, and assumed it had become a standard feature of modern cars. However, I can’t find any such thing on my 2011 Ford Galaxy; am I missing something? 

CE, Bielby, North Yorkshire

A. This automatic locking feature is not currently available on European Ford cars and it isn’t possible to have it retro-fitted.

Ford does make it available in other markets, though, as it is a popular security and crime-prevention measure in South Africa and the Americas because it stops rogues jumping into cars that are halted at traffic lights, for example.

A spokesman for Ford in the UK said there were plans to offer automatic locking on the new Mondeo launched later this year, and added: “We are increasingly looking to produce global cars, so features such as this one will become more available.”

The new Mondeo will be launched at the same time as its American counterpart — confusingly called the Fusion — and the two models will have about 80% of their parts in common.

Peugeot takes a different approach. Ten years ago it was one of the first manufacturers to fit automatic locking on all of its cars, and it is now a no-cost option on all new models. Drivers simply press a button on the dashboard to activate automatic locking; thereafter the doors lock by themselves whenever the car sets off.

Pulling the door handle from inside the car switches  the system off, thereby allowing occupants to open the door and leave the car.