It’s quite an eye-opener to dig back into the archives and read a vintage copy of Diesel Car, in this case the December 1991 edition, and see the real world of diesel motoring as it then was. Diesel’s UK market share had just then cracked ten per cent, with sales dominated by the diesel pioneers Peugeot, Ford, and CitroÎn, and combined monthly Peugeot/CitroÎn sales of 4,730 were well ahead of their diesel market share today.
But itís their performance and fuel economy that catch the eye, and bring home just how far we have come in the last 25 years. Kerb weights show significant differences, a typical mid-size saloon like Peugeot’s then popular 405 1.9 GRD turning the scales at some 1,040kg ñ 250kg lighter than today’s Focus 1.5 TDCi. What happened to that weight saving that we keep reading about? The 405’s DC test consumption was 45.5mpg, as against the ìofficialî 47.0mpg, comparing well with typical figures today for a 308 1.6 HDi 120 of around 50 to 55mpg. But the 405 struggled to 60mph in a weary 15.5 seconds, against today’s 308’s 9.7 seconds, and ran out of puff at 101mph against the 308’s 122mph. The 405 was no sluggard though, and, in its class, only an 81bhp Montego 2.0DLX had a clear power edge over the Peugeot’s 70bhp.
What’s really changed since then? Well, turbocharging was just then appearing and, for a modest extra £505, you could opt for the 405 GRD Turbo, with an extra 20bhp, and a massive 44lb ft torque boost, whilst the ìofficialî mpg figure only dropped by 1.4mpg. As those who remember those days will recall, the arrival of turbocharging radically improved the diesel image, and cars like the 405 Turbo Diesel Estate became popular company transport, as they swept past you arrogantly when overtaking, showing off their considerable mid-range torque. They were still pretty dirty though, and a heavy right foot would often produce a cloud of smoke, even in well-maintained cars, and they carried the ìdirty dieselî image that has rather stuck with the cars, even though 1992 brought Euro-1 emissions regulations that first limited particulate matter emissions.
But we’re thinking fuel economy, and we have probably three or four factors involved, often pulling in different directions. Car weights have increased steadily, partly as the result of increasing safety regulation that necessarily made cars more robust and crash-resistant, although at the expense of added weight. Aerodynamics generally improved, as their contribution to better fuel economy became more recognised. But engine power and efficiency also increased, and inevitably it was used as a selling tool by manufacturers, and the extra performance was inevitably used by drivers, again at the expense of fuel economy. If there’s one undeniable fact about all road vehicles, it is that you will use more fuel when you go faster. Not necessarily if you accelerate more quickly though, we should bear in mind, because the fuel that you use in accelerating from 30mph to 70mph is hardly related to how long you take accomplishing the exercise, and much more to the gears that you use, and whether or not you use of the engine’s most efficient speed band.
Let’s return to weight though; the fuel you used in accelerating is directly related to the weight of the car. You cannot change that, but you can attempt to minimise, or eliminate, wasteful and unnecessary acceleration. The most commonly observed waste of fuel is when drivers roar up to stopping points, like T-junctions and roundabouts, and then slam on their brakes to screech to a stop. I’ve a feeling that the high performance of some of today’s electric cars, with regenerative braking, is going to feed this habit, and it needs to be discouraged, for safety reasons alone.
So, inefficient as the engines of those early diesels were, and aerodynamically inefficient (although light in weight) as they mostly were, they achieved pretty impressive fuel economy. Much of that was down to how relatively sedately we drove back then, due to lack of available power, although that didn’t affect legal cruising speeds and journey times too much. Roads were quieter, and cross-country speeds were often higher than you can achieve on today’s congested roads, particularly if you chose a smart time to make those journeys. That’s still a valid point today. What time of day you choose to travel can have a big influence on your journey, how stress-free it is, and how much fuel you use. If your eyes are good, and you enjoy night driving, travelling at night can be hugely efficient. In the summer months, you can set the alarm early, catch the dawn, and be at your destination well before the inevitable traffic problems begin to appear.