Just a quick question Doc. I’m desperate to settle an argument as to what people used to do to stop diesel engine fuel freezing up in the winter. I say that they used to add some paraffin to the fuel, but a friend says that people also used to add petrol! Sounds very dodgy to me, and potentially dangerous. But then adding paraffin would have been using something that was untaxed, and therefore illegal, while petrol would at least have been legal. What’s the answer Doc?
Dan Deakin
Am I the only one who used to read The Beano? You are definitely right Dan, in that it was regularly advised in owner manuals for diesel cars to add a proportion of paraffin to diesel fuel in the winter. But, much to my own amazement, a Diesel Car reader recently quoted from an old Volkswagen (I think) manual that did advise adding petrol to stop the fuel lines gumming up! No problem with the petrol, tax-wise, but, as you say, the paraffin would have been untaxed. Was that why pink paraffin was sold back in those days, I am now wondering?
I can also tell you that truckers used to light fires under their engines in cold weather, to stop the fuel lines clogging up, back in the “good old days” as my dad used to call them! What clogs things up is the paraffin wax, at what’s called the plug point temperature, and adding thinner paraffin liquid, or kerosene, helps lower this temperature when the fuel gelling can start. As you probably know, the problem is generally avoided these days by introducing winter grade diesel, and often by using additives that help stop the wax from crystallising out. But in cold winds, which rapidly speed up the cooling process, and low temperatures, the problem can still occur, particularly when vehicles are switched off and parked up overnight.
The Doc
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There is another solution for commercial vehicles – a Thermoline fuel heater (go and Google it for more info). Developed by Raychem Corporation and sold today by e.g. Eberspacher, this in-line fuel heater heats fuel flowing from the tank to the filter to above the temperature that wax crystals (more a sludge than spiky crystals in reality)start to form. Extensive cold-chamber testing many years ago in the UK convincingly showed that such heaters would even clear a clogged filter allowing a bogged-down tractor unit to be restarted. Admittedly, improvements (higher cold filter plug point)in winter-grade fuel and warmer UK winters have reduced the probability of cold-weather problems.