On a still, cold February morning last year, we were camped at Trout Creek campsite, in the thick mountain forests near Superior. With eighteen inches of snow on the ground, it was the only campsite still open south of the I90 eastbound, and we'd been directed here by a Ranger who had found us huddled in our truck cab a few days previously in a rest area, trying to stay warm. We were eight months into our expedition to circumnavigate the world overland, and novices at being cold. Our route had brought us across Europe, through Ukraine, Kazakhstan, Mongolia, and the Russian Far East and to Seattle on the west coast of the USA. Even our month in Alaska, including a November visit to the Arctic Circle, had not been this cold.
Temperatures overnight had plunged to an icy minus 25 centigrade. We awoke to numb, cold, toes and a thick layer of ice on the inside of our roof tent. In the tent vestibule below us, the situation was no better, with ice creeping three quarters of the way up the sidewalls. We only know that it was minus 25 because we warmed the LCD screen on our thermometer with our hands to get a reading on the display. It had succumbed to the cold, just like our ball pens and computers, at about minus 18 the night before. Our water tank was frozen of course, and so was our toothpaste, shampoo, and washing up liquid. We should have anticipated problems when we noticed the cooking oil had thickened to a gel, and our gasoline stove had refused to vaporise enough gas to light.
Our adventure had tested us anew, and it had been fun, but now we rightly concluded that our situation had descended into dangerous territory. With no heating and no water we were skating, metaphorically, on thin ice.
We packed up carefully, avoiding skin contact with any metal tent parts, and jumped in. On the turn of the key, our Defender made a valiant attempt at starting, but the slow, laboured churning sounds suggested thickened engine oil. The battery indicators both glowed bright green, so we knew the batteries were both fully charged, but our truck wouldn't turn fast enough to start. It was one of those moments when you realise that what you do next will determine your outcome. If I continued to labour the engine, we would quickly run the batteries down, and be stranded. If we didn't start the motor, we'd be stranded anyway miles from the nearest help. What we needed was a way of helping the diesel to ignite at low revs.
Then a brainwave! I opened our side locker and rummaged in the storage bin until my hand folded around a familiar shape – a long cylinder of icy cold metal. Our Mongolian fly killer! A quick look on the side of the can confirmed my hopes – it was filled with butane as a propellant.
Removing the air filter box and filter, Helen turned the motor over while I sprayed fkykiller straight into the intake. Four slow turns, and the labouring diesel engine coughed into life.
It had been a close call.
As we drove away, I vowed to fill this crucial gap in my understanding of diesel and cold weather starting, to see if I could shed some light on why we'd had difficulties, even though I knew the diesel was good, having bought it a few days earlier in Seattle.
This is what we found out...
Whilst diesel has a reputation for providing low performance, diesel powered engines are a popular choice amongst overlanders for the same reasons they are popular amongst heavy duty vehicles: diesel is generally fuel efficient and produces a lot of power per cube of cylinder capacity, and the occasional problems with winter starting can be overcome. Adding turbochargers to diesel engines has largely eliminated the low performance issue, and modern diesels are as powerful, and certainly more torquey than their gas counterparts.
Both diesel and diesel engines have come a long way since the old days, when they were considered noisy and dirty. In the old days you would drive into a fuel station, find the pump marked diesel (normally with a large black stain on the ground around it), fill your tank, pay, and drive off. These days you are more likely to find you have a choice of different types of diesel. Knowing which one to choose can save you money on fuel consumption, wear and tear to your engine, and a costly rescue if you cannot run your engine because the diesel has 'waxed' or 'gelled' in your tank at low temperatures.
The diesel engine
Diesel is more dense (= more energy) than petrol and does not require the use of spark plugs. Instead the diesel engine compresses air in the cylinder chambers as the pistons rise (air gets hotter the more it is compressed) then a mist of diesel is injected directly into the hot air, and the high temperature of the air ignites the diesel. The resultant gases expand to force the piston down again, turning the crankshaft and powering the vehicle.
Choosing your diesel
The international standards organisation, the American Society for Testing and Materials (ASTM) rates diesel across six grades. The first two of which (and very occasionally, up to four) you may well find at the pumps, particularly in the United States, along with 'Premium' and Biodiesel. Grades 5 & 6 are usually only used as heating oils. In Australia & UK you are more likely to hear the terms 'summer' and 'winter' diesel.
Choosing Diesel No1 (or winter diesel) when temperatures are likely to drop below 5F/-12C when your vehicle is outside (including overnight) will significantly reduce the risk of your fuel gelling in the tank, but will give you less miles per gallon. As your fuel consumption will be reduced, if you are travelling in remote areas you will need to fill your tanks more frequently and will need to take this into account when planning and calculating the optimum distances you can travel. In winter conditions you may want to consider carrying extra fuel in jerry cans.
Diesel's dual purpose – lubrication. Second to powering the engine, diesel has a role in keeping the component parts, especially the fuel pump, lubricated. In the early days this was achieved through sulphur in the diesel. However, with modern understanding of the role of sulphur in the creation of acid rain, and resultant legislation, most diesel is now low or ultra low sulphur. Lower sulphur fuels (and thermally unstable fuels) have increased tendency to form carbon deposits on fuel injectors. Poor lubricity will result in increased wear, especially to fuel injection pumps and unit injectors. Although manufacturers offset the loss of the lubricating role of sulphur with the use of alternative additives, regular checking of all fuel systems should be an essential part of the overlanders' routine maintenance programme.
As Biodiesel has high lubricity it is commonly added in small quantities to other diesels instead of sulphur. However it also gels at higher temperatures, which will affect the temperature at which the fuel gels. Consequently, reliable manufacturers of diesel are unlikely to use biodiesel as an additive when and where the intended point of sale will be during severe winter conditions. However, if you are carrying spare fuel in auxiliary tanks or jerry cans across widely different climatic conditions you may want to carry your own fuel additives to lower the temperature at which diesel gels.
The role of wax in all diesel fuels is to improve the fuel's cetane rating (see below). However, as temperatures drop these natural waxes clump together and diesel turns to jelly. The diesel cannot flow along the fuel lines and the engine won't start due to fuel starvation. Gelling, or waxing, appears as a white or yellow deposit or a cloud in the diesel fuel. In countries with severe winter weather conditions they are generally used to dealing with this problem. If it happens to you during an overland expedition you may need help to get your vehicle to a heated garage where the raised temperature will enable the waxes in the diesel to return to their normal state and you will be able to start the engine again. This is usually done good naturedly and you may be laughed at for your misfortune. Expect to have to pay for the help received.
The Cetane rating (CN) measures a fuel's ignition quality, or the relative measure of interval between beginning of injection and autoignition of fuel. The higher the cetane rating the shorter the delay interval. CN40 is the minimum legal standard in most of the developed world, and most diesels will have a cetane rating of between 40 and 50. A rating of
Biodiesels can be used alone or in combinations with petrodiesels. Due to gelling at higher temperatures Biodiesels are more commonly available in warmer climates than colder climates. Most diesel engines will run on biodiesel without conversion, but check with manufacturer's guidelines before switching completely.
Although Biodiesels are promoted as the eco friendly option there are concerns among some environmentalists that, particularly in poor countries, precious farm land is being used to produce these fuels instead of much needed food crops.
Farm diesel (commonly known as red diesel because of the colour of the dye used) is cheaper than regular diesels due to being untaxed and having a high sulphur content. In most places it is illegal for use in road vehicles for tax reasons and the effect on the environment. It may also have an adverse effect on modern car engines and is not recommended except in an absolute emergency.
Truckers pumps in fuel stations generally dispense the same diesel as the regular pumps used by car drivers. The only difference is the increased pressure at which the diesel is pumped to allow for the quicker filling of larger tanks. Occasionally you may come across fuel stations solely for trucks. Drivers of the largest overland vehicles may find they can use these high pressure pumps, although so can smaller vehicles, providing only a very light pressure is applied to the pump lever.
Additives are available to improve the performance of diesel fuels, and include cetane improvers, detergents, smoke suppressants, flow improvers, and anti rust/anti corrosion. However most manufacturers use additives at the point of manufacturer and the use of further additives should only be necessary in extreme conditions or where there is significant doubt about the quality of the diesel purchased.
Storage and contamination
Diesel has a storage life of around 6-12 months, however high temperatures and contamination, particularly with water, will affect the quality and stability of the diesel fuel.
There is increased risk of buying fuel affected in this way in remote areas with low turnover sales, even in the US; they are unlikely to tell you how long the fuel has been in their tanks. Poorly maintained fuel pumps could also lead to contamination problems.
Where possible try to avoid buying diesel from locals who have bought their fuels from a fuel station but are selling it on from old tanks stored on their property.
Keep a record of when and where you bought any spare fuel being carried in auxiliary tanks or jerry cans in order to reduce the risk of using deteriorating fuel.
Finally, diesel is less volatile than petrol / gasoline and the two should never be mixed. Using petrol in a diesel engine will cause significant damage.
Want to get your diesel here?
Diesel & Overlanding – summary
Most overlanders will be able to purchase suitable diesel for their vehicle and their environment wherever they are. The issues to be aware of are:
MPG/KPL – diesel No.1 (winter rated diesels) will result in higher fuel consumption
Waxing – summer diesels wax at higher temperatures, so as temperatures drop, the risk of waxing increases
Cetane ratings – indicate the fuel's ignition quality, and should be between CN40 and CN50, but you probably don't need to buy premium diesel for its higher cetane rating
Biodiesels can be used alone in warmer climates (but check vehicle manufacturers recommendations) or mixed with petrodiesels except in colder climates
Contamination and long term storage will affect the quality of diesel, and are more likely to cause problems when using remote fuel stations with low stock turnover
Although additives can be used to lower the temperatures at which diesel waxes, extreme cold weather overlanding will require considerable additional personal and vehicle preparation.
So what was happening inside the engine of our truck that had us praying for good fortune in that frigid, remote forest last year?
We'll never know for sure of course, but here's our thoughts:
Our tank had been filled in Seattle with Diesel Number 1, not really knowing why we were doing so. We could have topped up with No 2, as it was available from the nozzle alongside the one we used. If we had in fact done so, we would almost certainly have needed outside help to move our truck, because it has a higher gel temperature than No1, which gels (waxes) between -21C and -28C. At -25C, our fuel was right on the cusp of this occurring, so most likely wax was just beginning to form in our fuel.
The cetane rating of a diesel indicates how fast it ignites when compressed, making starting easier and delivering nippier performance. Waxes are added to improve the cetane rating, making the ignition faster. It stands to reason that if waxes had started to separate out in our diesel, they would not be able to provide their intended boost to starting performance, hence our difficulties in getting ignition from a slow turning engine.
By spraying fly killer into the intake, we added an accelerant (butane) to the fuel entering the cylinders, and hey presto – ignition!
Another few degrees of temperature reduction and we would, for sure, have had fully waxed diesel in out tank and fuel lines, and a long hike out for help.
The learning is this. Make sure both you and your truck are prepared for the environments you'll be travelling through – especially if these include ones that can prove to be life threatening if you become stranded.
Preparing yourself includes knowing the things you need to know to keep your truck moving, and yourself safe.
Preparing your truck means making sure it's is equipped to operate in the conditions you may encounter.
Before we head back to Montana in February, we'll be adding tank and fuel line heaters to our rig!
This article was courteously provided by Paul and Helen of the Going Overland Expedition. If you're interested in reading more of their wisdom from the road, please visit their website at www.goingoverland.com