On 12 Jan, 16:02, Dave Osborne wrote:

Stupid, as in dangerous, ill-advised or just pointless?

Pointless. Diesel fuel doesn't "freeze", and it doesn't "freeze in the
pipes". What happens is that Summer-grade diesel contains waxes
(they're removed for deep-Winter grades), and these waxes freeze,
freezing out as fairly large crystals. As the crystals separate from
the diesel (i.e. they form "clots"), a little wax can go a long way to
stopping an engine that has a small fuel filter (with small pores) or
the valves of an injection pump. If you decant a small sample of
"waxed up, frozen diesel" you might not even be able to see the
difference, yet it's enough to block a filter (try filtering it
through cold filter paper though, and see what residue it leaves).

There's a lot that can be done to reduce this effect:

* Dewatered fuel. Water is generally bad here, but not so you'd
notice. A plug of water settling out in the bottom of a pipe bend and
freezing solid is more of a problem.

* Dewaxed fuel. Winter blends, which come in a range of severities.

* Heating the fuel, usually electrically (wrap band on the filter
casing). For mild UK Winters, this is enough. The injection pump is
warm enough already to not be a problem.

* Heating the fuel. Some Eastern European kit has a separate header
fuel tank that's heated by the engine (usually oil-heated, as engines
designed for this weather are often air-cooled). This tank contains
enough fuel to start and warm through the engine, and it has a mains-
powered plug-in heater for starting.

* Redesigning the injection pump, so that valves aren't jammed by wax
buildup. Mostly this involves smoothing out ports and paths so that
crystals aren't trapped to gradually build up, but are instead
continually washed through by the bulk fuel.

* Moving the fuel filter inside the engine bay. Trucks with chassis-
mounted filters suffer much worse than cars.

* Diluting the fuel with a convenient wax solvent, e.g. petrol. This
isn't about "antifreeze for fuels", it's just about dissolving that
small proportion of wax in a solvent that doesn't give it up so
easily.

In a heating boiler, there's no high-pressure injection system as for
a diesel engine, so clearances are bigger. A bit of wax isn't going to
stop it anyway.