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Is your care smoking from the exhaust - a guide on what to look for from Dave Chapman

Have you had that horrible moment when you look in the mirror and thought oh dear - was that me? I had a customer come in the other day, he had a VW Touareg. With a concerned expression he described how he had turned day into night for a driver when he put his foot on the throttle to pull away. Clouds of black smoke had engulfed the person behind him. I explained that black smoke was better then blue or white. It turned out to be a split in a hose that messed up the fuel/air mix.

So what can the different colours of exhaust fumes mean?

Black smoke is normally an indication that the fuel mix has gone wrong, the car is burning too much fuel. There a multitude of areas that can cause this on a modern car but it doesn't normally involve stripping down the main engine block.

White smoke can be seen on every car when it starts, big engine cars can take an age to heat up and clear this, on starting this is basically steam and normal. But if it continues then more investigation is required. The first thing I would be thinking is whether some coolant is leaking into the cylinders, and then burning with the fuel. That normally means a head gasket failure. Please don't hang around with diagnosing these problems. A full failure can cause overheating and the problems quickly escalate.

Blue smoke. We have all been behind a car with blue smoke, smelly - just like burnt oil. That sums it up really, engine oil is getting burnt with the fuel. This could be a head gasket or internal engine seals - either way this needs to be checked and fixed before the costs mount up.

You have smoke, what can you look for? Firstly, under the bonnet look for leaks. There shouldn't be any so take a bright torch and look for leaks around seals where components come together. Take a look under the car for drips or damp looking patches.

Check your liquid levels. Get the oil dip stick out, clean i

t with kitchen roll or similar, put it all the way in, take it out again and check against the marks on the dip stick. Is the oil thick and black or the preferred smooth and clear? Was the level of the oil right?

Check the coolant level, this shouldn't change if it needs topping up that means liquid is escaping somewhere - please get that checked out.

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