Cold
Engines
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any people know that frequent cold
starts, and short city trips, dramatically increases the fuel consumption of a
petrol car. But these types of trips are
also very hard on engine oil. It’s no
surprise that most manufacturers have two different service schedules - one for
“typical use” and one for “harsh” use.
It’s not always so clear, but “harsh” use doesn’t mean driving to
A “short journey” is basically any
trip up that is not long enough for everything to get up to normal operating
temperature. In the summer after the
engine has been run, this can be just five minutes and in the middle of the
British winter, this can be twenty five minutes. These are just ballpark figures - it does
vary! It also depends on the car, the
road, the driver, the weather, and a few other bits and pieces. There are a number of things that should get
up to normal operating temperature: engine oil, coolant, catalytic converter and the
exhaust.
Some cars, such as the Saab 2∙2 TiD, have an auxiliary
heating system designed to shorten the warm-up times. These can be in the form of electric heater
elements or an auxiliary fuel heater.
Water is an important
consideration here. Water is a
by-product of combustion – it’s kicked out of the exhaust. If the exhaust is hot, the water turns to
steam and the exhaust remains dry. If the
exhaust is cold, much of it remains as water vapour – the condensation you see
on a cold day. This water greatly
accelerates the rusting of the exhaust pipes.
The catalytic converter doesn’t
work when cold, and if the engine is misfiring, the ceramic can get coated in
unburnt petrol, which then burns when it gets hot, and can cause overheating (leading
to damage and a replacement catalytic converter). Generally speaking, this isn’t a problem,
except that water vapour accumulates in the cat. This can lead to the casing to rust. Catalytic converters sit right next to the
engine and generally get up to temperature very quickly, however even so, it’s
wise to try to look after them. They’re expensive,
ranging from a couple of hundred pounds to over a thousand, depending on the
car in question. They also wear out (but
I’ve never had one go on me, personally, they do wear out).
Similarly, the inside of an engine
also contains water. This mixes with the
engine oil, but hot oil turns the water to steam, which is then removed from
the engine. If the oil doesn’t get to
normal operating temperature, for a decent time, the oil gets more and more
contaminated with water. This
emulsifies, forming a white mayonnaise-like creamy stuff that can be found in
the oil of many city-bound cars condemned to a life of short trips. This mayo is a bad thing - it clogs the
engine oil ways up, leading to inadequate lubrication and engine failure.
The other very important
thing is that you do not stress the engine until the oil is up to normal
operating temperature. I treat my engines with kid gloves when
cold. Whilst this means you must not use
high engine speeds (up to half the maximum permitted engine speed as a
ballpark figure) it also means you do not
labour the engine. Labouring the engine is arguably worse than
using high engine speeds.
Starting
the Endura-E From Cold
This chart shows how the engine
speed behaves when cold and when Kermit’s “QuickClear” is both turned on and then off.
The data was sourced from Kermit’s
OBD-II Scanner unit.
The first record shows the engine
turning over at just over 400 rpm - this is whilst the starter motor was
engaged! Then, the engine speed
immediately jumps to approximately 1,750 rpm before it settled down to 1,200
rpm. It maintains this engine speed for
approximately thirty seconds, then the idle speed slowly drops to 1,100 rpm. After thirty six seconds, I turned the
QuickClear on, hence the drop in engine speed - note how the ECU compensates for this. You can also see the spike where I switched
QuickClear off, after approximately thirty seconds.