Recently there has been a great fuss, across the United States, United Kingdom and the European Union, about the discovery that diesel cars can pollute more than was thought, and that some models were designed to work differently under test conditions as opposed to normal use, leading the authorities (and the car owners) to a false understanding of how polluting a given car was. The reaction to these discoveries, has been a movement to ban (or prohibitively tax) diesel cars from city centres, and politicians are now demanding a wholesale move to petrol engined cars.
Before we do this, however, there needs to be a proper investigation into whether or not all the petrol engined models are actually any cleaner than the diesels. They are supposed to be, and when tested most petrol engined cars will appear to be clean, but that was also what was supposed to be true about the diesels. In the case of petrol engined cars, the comfortable assumptions about their low emissions needs to be checked, and thoroughly so.
Most especially with regard to BMW models.
Nearly all petrol-engined BMW cars (apart from the low powered "Minis") have a tendency to get through a fill of lubricating oil much more quickly than models from almost any other manufacturer. Some BMW cars come ready fitted with a special bracket in the boot to hold a spare can of oil, just in case the engine requires more during a given journey. Most other manufacturer's cars: you check the dipstick once a month and it doesn't usually need a top-up unless the car is several years old. If it does, it isn't usually a whole can that's needed. New BMWs frequently need a can a month. This oil isn't disappearing down some black hole: it is being burned, and the combustion products are entering the atmosphere. Lubricating oil is not formulated to be a fuel: it does not burn cleanly, and the combustion products include the very particulates and Highly Volatile Organics that are so deadly to human health when emitted by a diesel engine. In addition, the conditions which are burning the oil tend to involve high combustion pressures, which can also lead to the creation of excess nitrogen dioxide, another bad thing blamed on diesel cars.
Yet, when a BMW engine detects that it is being tested for emissions, it is somehow able to seamlessly turn off the oil burning: presumably by controlling the oil pump speed and thereby reducing oil pressure. Whether this reduction in oil pressure is displayed on the dashboard is another matter. In any objective test, this parameter needs to be measured independently of the car's potentially compromised, electronic intelligence.
Why is it like this? Well, for generations, BMW have been trying to please a particular customer base, and that customer base in turn has been adapting to the image of a typical BMW driver conveyed in the company's advertising and motor-sports sponsorship. This means that, whereas a Jaguar or Mercedes owner might revel in his car's smooth acceleration, a typical BMW driver enjoys something harsher and more abrupt. The engineering choices made to create an engine that can take being thrashed, involve high oil pressures and high engine compression ratios. The engine burns more oil than its more sedately-driven competitors.
It is a mistake to believe that an anti-diesel witch-hunt is going to lead to cleaner air in city centres if cars which burn inordinate quantities of lubricating oil are still allowed access.
Before we do this, however, there needs to be a proper investigation into whether or not all the petrol engined models are actually any cleaner than the diesels. They are supposed to be, and when tested most petrol engined cars will appear to be clean, but that was also what was supposed to be true about the diesels. In the case of petrol engined cars, the comfortable assumptions about their low emissions needs to be checked, and thoroughly so.
Most especially with regard to BMW models.
Nearly all petrol-engined BMW cars (apart from the low powered "Minis") have a tendency to get through a fill of lubricating oil much more quickly than models from almost any other manufacturer. Some BMW cars come ready fitted with a special bracket in the boot to hold a spare can of oil, just in case the engine requires more during a given journey. Most other manufacturer's cars: you check the dipstick once a month and it doesn't usually need a top-up unless the car is several years old. If it does, it isn't usually a whole can that's needed. New BMWs frequently need a can a month. This oil isn't disappearing down some black hole: it is being burned, and the combustion products are entering the atmosphere. Lubricating oil is not formulated to be a fuel: it does not burn cleanly, and the combustion products include the very particulates and Highly Volatile Organics that are so deadly to human health when emitted by a diesel engine. In addition, the conditions which are burning the oil tend to involve high combustion pressures, which can also lead to the creation of excess nitrogen dioxide, another bad thing blamed on diesel cars.
Yet, when a BMW engine detects that it is being tested for emissions, it is somehow able to seamlessly turn off the oil burning: presumably by controlling the oil pump speed and thereby reducing oil pressure. Whether this reduction in oil pressure is displayed on the dashboard is another matter. In any objective test, this parameter needs to be measured independently of the car's potentially compromised, electronic intelligence.
Why is it like this? Well, for generations, BMW have been trying to please a particular customer base, and that customer base in turn has been adapting to the image of a typical BMW driver conveyed in the company's advertising and motor-sports sponsorship. This means that, whereas a Jaguar or Mercedes owner might revel in his car's smooth acceleration, a typical BMW driver enjoys something harsher and more abrupt. The engineering choices made to create an engine that can take being thrashed, involve high oil pressures and high engine compression ratios. The engine burns more oil than its more sedately-driven competitors.
It is a mistake to believe that an anti-diesel witch-hunt is going to lead to cleaner air in city centres if cars which burn inordinate quantities of lubricating oil are still allowed access.
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