With winter fast approaching, and maybe even already with some readers by the time they read this, it’s time to think about how this sometimes cruel season affects our fuel economy. Referring to records of four varied vehicles we have run, over a total of 130,000 miles, the winter to summer variation appears to be fairly consistent. With an overall mean of near enough 50mpg, the summer average seems to rise by around three to four mpg, and the winter average falls by four to five mpg, and we can all expect some similar loss of economy. But your variation will depend on your type of motoring, and the average journey length, as it’s the warm-up period over the first five miles or so when the engine is cold that really drinks up extra fuel. Compared with petrol engines, diesels units don’t suffer from quite such an awful short period when the engine is spitting out steam and running on a very rich fuel mixture, although, to be fair, things have improved greatly in recent years with petrol fuel injection, compared with the days of carburettors and chokes.
Whether you run a diesel or petrol car, anything you can do to start the morning with a warmer engine than if it’s left out overnight totally at the mercy of the elements can help save fuel, reduce starting problems, and increase engine life. Cold starts in the winter are when the very worst of engine wear takes place, with the cold oil not in full circulation and slow to achieve that on account of its high viscosity. So it’s not a bad time to check when your last oil service took place and consider getting one done soon, possibly a bit early, and not leaving it until after the winter has passed. It’s worth pointing out that battery efficiency is hugely affected by temperature, and a garaged car with a warmer battery is always going to be a better starting proposition than one that has been sat on the drive all night. If your battery is marginal, then your pre-heater plugs won’t heat up properly and the lack of power will probably reduce the starter cranking speed. Maybe it’s not a lot of help to point out that countries with traditionally hard winters often supply cars with block heaters that allow you to plug in an electric heater, usually placed in the coolant circuit, to pre-heat your engine, accelerate oil circulation, improve warm-up, and clear frozen windows rapidly. Manufacturers and importers apparently don’t think British cars merit such equipment, but the predicted more severe winters might change attitudes, particularly when most engines are usually already manufactured ready to accept such engine heating units. You can find after-market engine heaters, (some are alternatively fixed to the oil sump and heat the oil rather than the coolant) but fitting may be a problem and there seems to be little enthusiasm for them in Britain. But do garage your car if at all possible, or protect it from the worst of the weather if it must stay out overnight, and do anything that helps to get the engine started quickly and safely on the road, rather that ticking over while you are clearing ice and snow from the windows.
But there has been some stunning progress in improved engine cooling systems over the last few years and the warm-up of some newer diesels is now amazingly fast. They usually employ more sophisticated coolant flow principles than the traditional engine-driven water pump and wax-filled thermostats, such as two-stage thermostats and fast-action thermostats with heating elements that can override or speed up normal coolant temperature initiated opening. Motorised coolant flow valves are replacing thermostats, along with variable flow electric water pumps, often operating in dual circuit cooling systems. Typically, cylinder head coolant circulation is shut down at start-up, and until the coolant reaches 95 degrees Celsius, achieving faster warm-up and more efficient combustion. Much of this technology offers double benefits in that cold engine emissions are also greatly reduced, helping to meet tighter Euro 6 regulations, along with the notable savings in fuel consumption. EGR (exhaust gas recirculation) systems also play a part in faster warm-up, and some engines also use alternator power to operate relatively low power, but critically located coolant circuit immersion heaters. But it goes without saying (or does it?) that a brisk one mile walk will probably do you more good, and your engine a lot less harm, than a very short drive to the shops and back!