Diesel urban myth no. 1: they don’t start in the cold

October 30, 2008 -- Filed under Clean Diesel by Louis-Alain Richard

The world of cars, like society in general, is not safe from certain urban myths, certain tenacious prejudices that can’t be got rid of. For example, some people still believe in planned obsolescence while others are convinced that adding a little bottle of liquid with anti-friction properties can extend the lifespan of their engine by hundreds of thousands of kilometres. Here, on TDI Curious, we do not intend to correct all these car myths, although this could be quite interesting, but we will try to rectify those that relate to diesels, and, secondarily, those that relate to responsible driving issues such as fuel economy and new technologies.

I have already raised one of these subjects in this post about supposed “fuel savers“. In this blog, we will consider the cold-starting problems that diesel engines had in both the old days and today.

The good old days

In the past, let’s say before 1990, diesel engines had only one tool for starting in the serious cold: little things called “glowplugs”. These little electrically heated rods (just like stove-top elements) are placed in the combustion chamber and preheat it before the starting process is engaged. Because a diesel engine depends on the heat of the compressed air in the cylinder to ignite the fuel, a bit of additional heat is welcome.

In the 1970s, glowplugs were required to be in operation for one minute BEFORE starting the engine. Which is certainly not practical when you’re already going to be late for work…

At the beginning of the 1980s, the preheating time had been reduced to less than 10 seconds even in very serious cold, thanks to new glowplugs.

Today

With the advent of electronic injection in diesel engines, glowplugs became practically useless for starting, except in the very serious cold (under -24°C). And no, the wind-chill factor doesn’t count: it’s -24°C on the thermometer, not on TV! At these arctic temperatures, the most recent glowplugs are nevertheless able to reach 1,000°C in less than 2 seconds.

Glowplugs are no longer necessary in (more) normal weather because it is now possible to inject the fuel in several small doses that are easier to ignite than just one dose. Now, starting a modern diesel is therefore not much different than it is with gasoline engines. You turn the key, and you’re off.

This is a “non-starter”

Now, everything that I’ve said above applies to an engine in good running condition. When an engine ages, no matter which kind (gasoline or diesel), it can become more difficult to start. However, you have to consider that the gasoline engine is less subject to difficult starts (due to neglect) because the ignition is done with a spark and the gas vaporises (which requires only explosion). In the case of old diesel engines with a great deal of mileage, it is true that wear can make starting in very serious cold more difficult, but this is often the fault of a negligent owner. This can be compensated for by always plugging in the engine heater; however, the replacement of certain components (battery, starter, plugs) puts things back in place.

These days, thanks to new cylinder pressure sensors, wear is now taken into account in the starting parameters. The result: no matter the age of the engine, starting and energy efficiency will be consistent during its lifespan.

Did this subject warm you up? This is the place discuss such matters.

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