While the phrase 'glow plugs and waxing' sounds like a treatment you'd find on the itinerary of
services at an up-market spa, it actually refers to components of a diesel engine and a condition which
affects diesel fuel. First, let's define what these two things are.
- Glow Plugs
A glow plug (sometimes alternatively spelled 'glowplug', but there's no difference) is an electrically
powered heating instrument used to assist the start of diesel engines in colder weather. A bit like
the way a toaster uses electrical resistance in filaments to heat bread, a glowplug uses filaments to
heat air just before it's taken into the cylinder to make autoignition of the fuel easier.
- Waxing
Wax molecules are natural components of the crude oil from which diesel is produced, and all diesel
fuels contain them. But in extreme conditions - sub-zero air temperatures for example - the wax can
start to crystallise. The process whereby the wax molecules in the diesel begin to solidify is known
as 'waxing'.
Why is there Wax in Diesel?
The wax in the diesel has a high cetane value - cetane is a hydrocarbon which detonates readily under
compression, a property which is valuable in diesel fuel. Normally, the wax is a liquid and blends with
the diesel with no problem. But at very low temperatures it begins to solidify - never truly freezing,
but becoming thick enough to stop the flow of fuel in your engine.
Essentially, the wax in your diesel makes the engine more efficient and cleaner, bringing down the
temperature of autoignition which takes stress of your engine's working parts and preserves the life of
your car. The penalty you pay for the advantages offered by the wax is its tendency to congeal when
chilled. It's a fair trade, really.
Why is Waxing Harmful?
If a sufficient amount of wax molecules crystallise, fuel lines, filters and strainers can become
clogged, strangling the power of the engine and rendering it inoperable. This is a serious problem, so
serious that in many parts of the world - New Zealand for example - diesel manufactures are required by
law to produce two types of diesel, one for the winter and one for the summer. The winter diesel is
designed to lower the temperature at which the wax in the fuel begins to solidify, known as the 'cloud
temperature' and reduce the risk of waxing.
Diesel won't freeze as such, but if the temperature drops really low there's a possibility that the
wax crystals will build up enough and the engine will either stop, fail to start, or be very difficult
to start.
How do Glow Plugs Help?
Glowplugs are designed to heat the cylinder and the engine block, so that ignition of fuel is a little
easier. The glowplugs can't help if the diesel has waxed in the tank, but if the fuel can get to the
cylinder - if the fuel lines aren't too blocked and the filters are working - then the glowplugs will be
able to help ignite the fuel, and the temperature from the ignition and the exhaust system should go some
way to sorting the problem out naturally.
Symptoms/What to Look Out For
Here's a quick list of things to look out for if you suspect your diesel is waxing:
- As already mentioned, your car will not start, or will be really reluctant to start. This is due
to the fuel starvation caused by the wax, and will probably be in the morning, after the car has been
stationary for a long period of time.
- Check the dipstick. If the oil has frozen, then the chances are the wax in your diesel has
solidified too.
- The wax will appear as a white or yellow deposit in the diesel. The diesel will look cloudy. It
goes without saying that you would have to drain the fuel tank to check this.
- The fuel filters are waxy.
As you can see, it really takes a mechanic to spot if your diesel is waxing, because it mainly
affects the internal workings of the engine. There are no real external signs; if you're car is failing
to start, you can't check the smoke for symptoms. Often the only sign that there's a problem with your
fuel is that the car won't start at all. To find out any more than that, you'll probably have to consult
a specialist.
How You can Help Prevent Waxing
Remember that the best cure for waxing is prevention. When the weather is exceptionally cold, there
are a few precautions you should take to make sure you can start your car easily in the morning.
- Store your car under a shed or with a tarpaulin sheet at night. Exposed cars will lose their
residual heat far quicker than covered cars.
- Make sure the lubricating oil in your engine is appropriate for cold weather operation. Your car
will be even harder to start if the oil has waxed too, so make sure you're using the right grade.
- Check the dipstick before starting your car. If the oil is solid, don't start the engine.
- Change the oil filter. A new filter might be a bit more tolerant towards wax molecules than an
older, partially clogged one.
- Insulate the fuel tank, filters and fuel lines. This can be done professionally for a minimal
cost, or you can simply improvise with blankets and sheets.
If you're Diesel or Oil has Waxed…
If you're fuel waxes, it's not always the end of the world. With a little patience, it can be coaxed
back to life quite simply.
- Check if the oil is fluid or frozen using the dipstick. If it's frozen, it'll need to be warmed
up before the engine is started.
- Warm the oil with a blow heater or steam cleaner if you have access to one. If not, use the
exhaust from another car, this will help soften the oil and wax.
- Once the oil has become fluid, try starting the engine. If the engine fails to start, check the
fuel filter for signs of wax. If the fuel is hazy or reluctant to flow, then warm the filter body and
the fuel lines. As above, use a blow heater or steam cleaner, or the exhaust from an already running
car.
- Once you get the engine started, idle it for a while and let it warm through. This will begin to
undo the clogging of the wax and prevent further blockages.
Having said all that, waxing is a pretty uncommon issue these days. The UK's winters don't really get
cold enough for long enough periods of time to allow the wax molecules to crystallise in large numbers.
Fuel manufacturers also offer seasonal diesel. You might not even realise it, but the diesel you put in
your tank in December is different from the diesel you use in August. 'Winterised' diesel as it's known
has a lower crystallisation point, and this has virtually eliminated the problem of waxing in the UK. But
use a little common sense; if it dropped to -15 degrees overnight and your car was parked on the road, I
shouldn't take a mechanic to figure out why it's slow to start!