The winter months are here, and we’re all going to see some drop in our mpg figures, although this depends very much on what kind of motoring we indulge in. All other things being equal, there’s no big loss of engine efficiency other than in the real extremes of low temperature, and it’s just the extra fuel used in warming up a cold engine that takes its toll. There’s no really significant extra usage of fuel involved in operating electrical accessories, like lighting, heating, heated windscreens, and windscreen wipers, or even entertainment systems, so to get the best miles out of our fuel in the winter months, we really need to focus on the issue of the cold engine.

All in all, we’re talking about a heavy lump of around 200 kilograms, composed of the engine itself, the transmission, and the fluids like engine coolant and oils. All aluminium engines may be as much as 50 kilograms lighter but, interestingly, the fuel-derived heat energy to heat up one kilogram of aluminium is around twice that for one kilogram of iron, so the heat required to warm up a high aluminium content engine is not all that different from one that’s mostly cast iron. The actual figures for how much fuel is used to heat a cold engine are hard to come by, but your temperature gauge will tell you that it’s significant, and in winter the needle will possibly not hit that 90 degrees Celsius average running temperature for perhaps six to eight miles, instead of three or four miles in warmer months.

So, the challenge is really to minimise the extra fuel used, and that usually means keeping your car as warm as you can overnight. We’re all aware of the wind chill factor, and if you can’t get your car into a warm garage ñ and those with garages attached to their house are best off ñ then even some help to keep a cold wind off it will reduce the cooling effect of overnight sub-zero temperatures. So parking at the side of the house is far better than leaving the car on an open, windy, driveway, and it will also help keep frost and snow off. Unfortunately, it’s not that practical or safe to talk of insulating the engine with a blanket or something that might help reduce heat loss from the engine, so that’s best left alone, and neither is blanking off part of the radiator inlet advisable.

But if you want to take advantage of today’s latest oil technology, investigate the possibility that your car’s engine can use one of the many low viscosity 0w-30 oils now specified for many new cars, which are backwards compatible with many older engines now using 5w-30 oils. These thinner synthetic oils circulate around a cold engine, whilst reducing friction and gaining marginally better fuel economy in all temperatures, with no danger of problems in warmer weather.

So now we come to how best to warm up a very cold engine, bringing us first to the big ìno-noî, of warming the engine up on the driveway, or on the road outside your house. It’s not good for the engine, pretty ineffective, and wastes fuel. The best way is to get your car quickly out on the road, once you’ve cleared any frosted windows or snow, or with the aid of de-icer spray and a scraper. This is when some forward thinking regarding your route to work, or the shops, can be of benefit. You want to get that engine working, and the oil and coolant hot, as soon as possible, so driving 400 yards to some traffic lights or straight into busy stop-go traffic is best avoided, if possible. Take a hard look at your usual route and search for an alternative with more open roads, and fewer likely hold-ups, even if it’s a mile or two longer. You might discover a new and stress-free way to your destination that uses less fuel, and is also kinder to your engine. Keep your engine speed in the 1,500 to 2,500rpm range whilst your engine is warming up, and your speeds moderate, and you’ll be doing the best you can for your engine, as well as your pocket.

Victor Harman