January 17, 2007
By Jim Kerr
There is a lot of interest in diesel powered vehicles right now, probably due to higher fuel prices and the higher efficiency of diesel engines. One of the concerns for many drivers new to diesel vehicles is cold weather driveability. Will they start fine? Will they produce heat? Are they a good winter vehicle? The answer to all three of these questions is “YES”. Let’s see what the manufacturers are doing with diesels to make them suitable for cold weather driving.
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Diesels do take a lot of power to crank over. While a typical V8 gas engine may use about 300 to 400 amps electrical power in the starter to crank the engine at temperatures below minus 20C, a diesel starter will use almost double that. Most of the power is used to compress the air. Gasoline engines have compression ratios around 9.5:1 (the amount of times the air is squeezed or compressed in the cylinder during the compression stroke). Diesel engines use compression ratios of 16:1 up to about 20:1. The higher compression ratios used in diesel engines gives them better efficiency, but makes them harder to crank.
Diesel vehicles have bigger batteries, larger diameter battery cables and heavy-duty starters for cold weather cranking. Many large V8 diesel-powered vehicles will use two batteries to provide the electrical power for cranking the engine. Just as with gas-powered vehicles, cold weather decreases the battery power available. In colder parts of Canada, battery blankets are often installed around batteries so they can be plugged in at the same time as the block heater to keep the battery warm.
High diesel engine compression ratios do something else – it heats the air, which is used to ignite the fuel. Gasoline engines use sparkplugs to ignite the fuel already in the cylinder. Diesel engines heat the air by compressing it and then fuel is injected into the hot air, which starts it burning immediately. The engine must crank over fast enough to heat the air or a diesel won’t start. Minimum cranking speed for many diesel engines is about 100 rpm. Below that, the air cools off to fast and the fuel doesn’t ignite.
Preheaters are used on most diesel engines to help heat the air during start up. Intake manifold heaters use an electrical coil inside the intake manifold to heat the air as it enters the engine. Glow plugs are individual heaters screwed into each cylinder that glow red hot during engine cranking. Both these heaters operate for only a few seconds during engine starting. If they were to operate for longer periods, they would burn out, which was common before computer controls took over the task of monitoring and operating heater control. If an intake heater or glow plugs are not working, the engine may be difficult to start, run rough and create white smoke during starting and initial operation. Once the cylinders warm up, the engine will run fine.
One of the “tricks” to starting any engine during cold weather is to crank the engine as soon as the glow plugs turn off. Wait a few seconds and the glow plugs and air will have cooled off again. Some vehicles have a “wait to start” or “glowplug” light on the dash. When the light goes out, crank the engine immediately. If you miss it, turn the key off for a few seconds to power the computer down and then turn the key on again to cycle the heaters again. Many current engine computers will only cycle the heaters once until you start cranking the engine. Then they will cycle them again, but they start better if you crank the engine at the right time.
Some vehicles don’t have any heater indication lights on the dash. Wait about five seconds after turning the key on before cranking the engine to allow the glow plugs to cycle. During extremely cold weather (minus 40C), I will usually cycle the key and glow plugs twice to help with starting. Using this technique, I have started diesel engines that have sat for several days at minus 45C temperatures without them being plugged in. I wouldn’t recommend this, but they have started!
One starting aid you don’t want to use is ether. In the past, ether was used on industrial and commercial engines because it would ignite at low temperatures and low compression pressures to warm the cylinders. Most modern industrial engines no longer use ether as a starting aid. Glow plugs and intake heaters can ignite the ether at the wrong time. If you are lucky, it may just backfire. Often, it can blow an intake manifold off the engine or break pistons and connecting rods. Diesel engines are expensive to repair because of the heavy-duty parts used in them. Never use ether or any other starting chemical to help start a diesel engine. If it isn’t starting, then it is usually caused by weak batteries, poor battery cable connections or inoperative glow plugs.
Diesel engines don’t produce a lot of heat when idling. That is because they aren’t using much fuel. Gasoline engines, with their aluminium blocks and electronic fuel injection suffer from the same problems. On the road, diesels are just as good in winter as any other vehicle. In Europe, diesel powered vehicles are extremely popular. Higher fuel prices are now attracting new diesel owners to these higher efficiency powerplants here.