Reference the article “Dodgy Audi Advice?” in the July 2013 edition. I had a couple of VW Golf Mk1s in the early 1980s and the Volkswagen handbook clearly stated that, to prevent waxing, a 25 per cent petrol to Derv mix was recommended for extreme cold weather.

My car stood out on an airfield car park for a week (at -20 degrees Celsius) and, although the engine started, the accelerator was inactive due to fuel waxing. A (very slow) visit to the nearest garage and a top up with petrol solved the problem.

I subsequently obtained a diesel additive from Silkolene which solved the problem. One egg cup full per tank fill was the dosage, I seem to remember. Fuel quality has improved since those days. Great magazine, keep up the good work.

David Warner-Howard

Many thanks for the further input. It does amaze me that attitudes to fuels were relatively so lax back in the 80s, but then it just shows the progress that has been made in cleaning up diesel.

I wonder what the manufacturer approved technique for avoiding waxing was in really cold places, like Canada, Finland, and Arctic Russia. I believe that they left their engines running 24 hours in some of those places, because once the sump oil cooled and went thick, you couldn’t re-start the engine without lighting a fire under the sump – which was often necessary!

That’s where/when/why synthetic engine oils were first invented, I believe, for aeronautical engines flying in very cold conditions. In such cold countries it is quite common practice to have block heaters that are plugged into mains electricity – overnight generally, but sometimes daytime as well – which most commonly are in the form of a heating element direct into a cylinder block water passage (often in place of a core plug) or into a radiator or heater hose, often then with a circulating pump.

There are also oil sump heaters, including magnetic ones that cling to the sump pan – well, they cling as long as your sump is not aluminium or non-ferrous alloy, that is! In places like northern Canada, electric outlets are frequently provided in car parks. Engine heaters are actually elegantly simple, inexpensive, effective devices. In cold weather, there are all kinds of benefits to a pre-warmed engine: reduced emissions; improved fuel economy; less wear and tear on engine components, starter and battery; and most importantly, hot air out of the heater sooner.

So I’m a little surprised that European manufacturers (who must offer such block heaters in the coldest parts of Europe) have not offered such facilities Europe-wide. It’s left to the long-established UK firm of Kenlowe to offer an after-market product, which can obviously save you a bit of fuel on cold starts, using cheap mains electricity with no excise duty applied.

But then (cynical me) there would be no gain shown in the published EC combined figures, as these are obtained on a car and engine already pre-warmed to 30 degrees Celsius. Just some passing thoughts on cold starting David! I’m glad that you enjoy the magazine, and the ramblings of old fogies like me!

Best regards,

Doc

Waste Recycling

Please excuse a letter from someone relatively ignorant on matters of engine combustion and its chemistry, but I’ve long been puzzled by the practice of exhaust gas recirculation (EGR). It sounds a touch to me like the widespread oriental practice of drinking a glass of one’s own urine daily. I won’t go into the details of that, but it is a widely accepted practice in India, China and Japan. Like EGR, it makes total nonsense to me to take a waste product and send it back to where it came from!

How does it make sense, I ask, for an engine that depends on oxygen in the air, and fuel, to produce its power to replace some of that oxygen with dirty exhaust gas? It’s long been suggested that many of the environmental measures to reduce engine pollution have stifled engine power and increased fuel consumption, and I’m wondering, Doctor, if you might try and make sense of it (if there is any sense in it) for me, and probably a good number of other Diesel Car readers!

Ben Harris

Thanks for the letter Ben – it’s something I’ve never actually been asked about before.

Firstly, it’s fair to say that the replacement of air and its oxygen supposedly does no great harm to the efficiency of combustion, because the diesel engine generally runs on what is called “excess air.” That means that there’s more than enough air and oxygen to burn all the fuel, as compared with a petrol engine, where there are limits to how much petrol can be burnt imposed by the amount of oxygen available.

One of the side-effects of having this excess air, though, is that the heat of combustion oxidises some of the nitrogen in the air to nitrous oxide and nitric oxide, or NOx, as these mixed oxides of nitrogen are termed, which are very nasty pollutants that are bad for the human lungs, and things like trees and plants. If you send some exhaust gas back into the engine, in place of some air, and particularly if you cool the re-circulated exhaust gas, you get a significant reduction in the production of NOx.

There are certain engine conditions when the EGR process works well and others when it doesn’t, so the whole thing is controlled by the ECU and various valves and vacuum units, to make the process as efficient as possible, bypassing the EGR system at times. As we well know though, EGR systems are prone to getting blocked up, often as a result of lots of short runs, and/or using poor fuels and engine oils that lack the additives to keep EGR systems clear.

We also know that bypassing EGR systems, or defeating their operation in other ways, can make an engine apparently run better, and more economically, but at the expense of greater production of NOx, and it’s technically illegal, as well.

I don’t know how the new systems using urea additives to remove NOx will develop, but I’m wondering if the end result (and I’m open to correction on this!) might just be the death of EGR, something about which there would be no great mourning. I’m going to find out as much as I can about this cheering prospect.

Meanwhile, I hope that this relatively brief reply answers your questions.

Doc Diesel

Contact the Doc

Send a letter using good old snail mail to: Doctor Diesel, Diesel Car Magazine, 40 Nevendon Road, Basildon, Essen, SS13 1AW.

Send an email to: thedoctor@dieselcarmagazine.co.uk

Or use the contact box on the website.