ave a wax free 1987
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Suction fed filters, and there are more engines with these around, can wax up at just below freezing, even with winter grade fuel. Today's reliable cab heaters are a satisfactory answer
I Are UK winters getting colder — or re there more diesel powered vehicles hrith non-pump fed suction fuel systems or is the quality of winter-grade diesel ailing? Many operators of diesels must e asking these questions as the incilence of "waxed-up" fuel filters inreases every winter.
Only a meteorological expert can ansver to the severity of recent British vinters — on balance they've probably lot got a lot colder over the last few rears. On the question of increased lumbers of non-lift pump equipped diesel vehicles — the answer is a resounding res. The vast upsurge in demand for carlerived light vans and diesel cars has ;eel) to this.
Vehicles of this type have simple fuel eed systems with no-lift pump, which -ely on suction through the filter. Thus in nany instances the suction fed system an suffer the effects of fuel waxing at .emperatures not much above freezing. this occurs even though UK winter ;rade diesel fuel has a cold filter plug point (CFPP) of —9°C.
On the question of fuel quality, worldvide standards are being lowered and the :rucial cetane levels are set to be further educed in the future. Thus in simple erms dery is not as combustible as it mce was — and this is set to worsen. In vinter operators have to be on their toes o prevent fuel problems.
Most vehicle fuel systems have water rap filters — these should be inspected/Irained far more frequently than in the summer to prevent icing. Also it only :akes a minute amount of water to reach the injection pump to cause expensive problems. Similarly even with diesels that run low mileages, it is well worth :banging the fuel filters to ensure mini-num obstruction and maximum system performance through the cold weather.
Very cold weather brings particular problems for diesels — fuel waxing. The explosive growth in diesel car/light van sales will see this winter with thousands pf drivers with compression ignition engines facing these difficulties for the first time.
The UK, as befits its relatively mild winter weather status, has one of the lowest winter fuel CFPP levels in Europe of —9°C. But the reducing quality of diesel has compounded this problem. In the early 1960s, according to tests made by industry experts, the cloud point (the temperature at which wax starts to form) was —17°C. Recent tests showed that in the Eighties cloud point of diesel was up to —1°C.
At very low temperatures diesel turns into a waxy syrup which blocks fuel filters and stops the engine, but well before the extreme cold which will turn the fuel solid, wax crystals form in the liquid which blocks filters and stop the flow. Dependent on the vehicle's fuel system design. CHI' can be reached at temperatures well above —9°C.
In a suction fed diesel car or light van . CFPP is effectively raised by anything up to 8°C. Thus certain light diesel vehicles can be in fuel waxing problems at barely less than 0°C.
Fuel waxing causes filters to choke very rapidly as the wax crystals which precipitate out of the fuel are considerably larger than the filter element holes. A normal wax particle which forms in diesel fuel during cold weather is about a tenth of a millimeter across — far larger than the 5 micron holes in the element.
Fuel waxing problems can be minimised. There are obvious factors to be considered. Often the vehicle designers' work on the fuel system has left filters and fuel lines exposed to the worst that wind chill can do. Where possible fuel filters should be repositioned to shield them from the elements — the same applies to the main pipe runs from the tank. Overnight in extreme conditions vehicles should be parked under cover. Where this is not possible at least the fuel tank and line side of the truck should be positioned away from the prevailing wind overnight. Also keeping the fuel tank full will prevent excessive condensation forming when the vehicle is parked for long periods.
Many operators used to swear by the addition of paraffin to the fuel tank to depress the temperatures at which wax was formed. This is a risky business unless you know what you are doing. And there is an additional drawback — it is illegal unless duty is paid on the paraffin used for this purpose.
Another method is fuel flow improvers — often these are expensive. Also they are difficult to monitor — the driver has to add the correct amount every time he fills up.
A more satisfactory method of keeping fuel waxing problems at bay is a fuel heater. Some operators will groan at the thought — they're the ones that suffered at the hands of the earlier non or unreliably regulated models. These either did not work or had a tendency to place an excessive electrical load on the vehicle's system.
Today there are at least two more sophisticated self-regulating models available on the UK market. Both Lucas CAV's D-Wax and the newly launched Stanadyne Aand T-Series heaters are compact units said to be easy to fit.
Cheapest of these is the Stanadyne ASeries line heaters, which are available in 12 or 24-volt forms. In 24-volt form this simple unit is said to be suitable for up to medium-size trucks. No fuel flow figures are quoted by the manufacturer but Stanadyne European management reckons they are suitable for diesels up to 1121149kW (150/200hp).
These A-Series line heaters will not be effective, however, for Cummins or DDA engines with mechanical type injection systems. These systems have a very high flow rate — the bulk of the fuel being returned to the tank. For these engines and other more powerful trucks Stanadyne has its T-range of fuel heaters. These are designed for long service life in truck applications and carry a three-year warranty.
Stanadyne is a major supplier of fuel heaters in the demanding North American market. The company, through its Trappes, France, operation supplies Citroen, Peugeot and John Deere among others with fuel heaters.
Now Stanadyne's range is available in the UK. Priced from £29, the A-Series line heaters are competitively priced. The larger T-range model pricing reflects its premium specification at .C2504300.
Stanadyne offers the 1-range in two heater forms, the all-electric 1-Series and the TEC range which combines electric heating with a coolant heat exchanger. The 1-Series comes in ratings of 350, 500 or 700 Watts (at 12 or 24 volts) according to engine maximum fuel flow. Operation is automatic, the heater switching on whenever an inlet sensor detects fuel temperature below 8°C, and switching off again once it reaches 25°C. . A heater-operating warning light is provided, together with an override switch.
Among the advantages, says Stanadyne, of an electric fuel heater is that it provides protection against waxing even during cold starts, which can be a critical operation where equipment has been left outdoors in cold-soak conditions.
Once the engine is running and the system is warmed through, the coolant heat exchanger type of fuel heater can provide sufficient heat for the fuel. This is the principle of the Stanadyne TEC range which combines electric and coolant heaters in a single housing.
The electrical element works within the same fuel temperature extremes as the 1-Series. But since the coolant will normally provide enough heat in normal running, it operates mainly during cold starting and warm-up or in the most severe conditions.
Stanadyne's research in the USA has shown that large vehicles can take up to half an hour to warm up to a stabilised running condition. The coolant exchanger contains an automatic bypass valve which opens up during warm weather operation, when fuel heating is not needed.
Electrical fuel heating can be used before engine starting. This factor can be crucial in very cold conditions (below about —20°C) when the line pressure drop through a diesel fuel filter can become unacceptable within one minute of starting — long before any coolant operated fuel heater is effective.
Both the Stanadyne fuel heater ranges are fitted in the fuel supply line upstream of the fuel filters. The Lucas CAV DWax actually fits into the fuel filter assembly sandwich fashion between the head and the filter body.
To cope with higher fuel flows the DWax units can be "stacked" or used on twin-head filters. The pricing of the DWax units, which are fully automatic and self-regulating, is comparable to that of the Stanadyne A-Series line heaters.