Update to original Post titled Cold Starting Diesels November 12, 2013
It’s all about the battery.
Diesels take a lot of power to crank them due to the high-compression in the engines (Typically 20:1) .
That’s typically twice that of a comparable petrol engine (Typically 9:1)
Diesel vehicles always have bigger batteries than petrol engines,
They are fitted with larger diameter battery cables and heavier-duty starters for cold weather cranking. They need to be “meaty” as they need to spin the motor at a decent cranking speed to start the engine (typically 100-150 RPM).TIP:-
Don’t forget to hold the clutch in when cranking the engine.
The strain on the battery is plenty enough without it also having to stir the cold thick oil in the gear box.
Pre-heaters and Glow plugs
The high-compression in a diesel is what heats the fuel to combustion temperature (think fire piston) but even then it’s sometimes not enough if it’s too cold a day / night.
Usually the electronics in a high pressure common rail diesel engine will sense the cold and trigger glow plugs whose job is to preheat the air in the cylinder. On bigger engines you may also find inlet manifold heaters.
If an intake heater or glow plugs are not working, the engine may be difficult to start, run rough and create white smoke during starting and initial operation. Once the cylinders warm up, the engine will run fine.
In the cold, you need to be cranking the instant the glows turn off.
Any delay in cranking will allow the air to cool down.
If it is EXTREMELY cold, cycle the glow plug / pre-heater a couple of times BUT be cautioned, in some modern vehicles it needs you to crank the engine BEFORE the glow circuit is re-enabled. All it takes is a short spin in some vehicles to reset the circuits.
You can buy spray assists to start the engine like ether based cold starts.
Whilst they do work, if the engine backfires, it can do SERIOUS (Big Buck) DAMAGE to the inlet manifolds.
Battery output shrinks DRAMATICALLY as it chills down.
A battery that will typically deliver:-
100 percent capacity at 27°C (80°F)
75 percent at just over 4°C (40°F)
50 percent at –18°C (0°F)
Freezing a battery will also make a battery useless.
The good news is that a charged battery won’t usually freeze due to the high specific gravity of the battery fluid. It’s got to be DAMN cold for one to freeze though typically under -50 C.
CAUTION. Near frozen batteries have been known to EXPLODE when worked too hard. Let alone if you try to fast charge them.
Hot Water “Fix”
I watched one day as a person poured hot water over their chilled battery to get a bit more power out of it. For some reason he started crying as the cold plastic case of the battery split and dumped battery acid all over his starter motor and solenoid. Personally this is not a plan I subscribe too.
Lead acid batteries usually only last 4-6 years no matter how well you look after them.
Only living on a narrow boat I’ve seen a whole new level of abuse to batteries as they are often left for the 6 months of winter without any recharge. As a battery sits gently discharging, especially in the cold, it forms lead sulphides on the battery plates. Leave it for a long time and these crystal sulphides just won’t go away. Thus you lose battery capacity when you need it the most i.e. on start-up.
Then there is the problem of charging them. To prolong their life you MUST use an intelligent charger. That is a charger that changes mode as it looks after the batteries going from a powerful BULK charge, to an absorption (trickle charge), and finally a float charge that is just enough to maintain the battery at an optimum state. We’re now talking high-tech and not something easy to repair or find in your local 7-11.
Only consider in a time when resupply is more a question of what you can find.
Eventually anything you liberate will be well into a sulphide cycle so:-
A “Memo” to long-term preppers.
Only store dry unused cells that need filling with distilled water and charging from new.
So what about charging from the alternator, is that better?
Working a battery is always better than letting it sit rotting away except as the ambient temperature drops, it takes longer to charge up.
Lead acid is reasonably forgiving when it comes to temperature extremes, as the starter batteries in our cars reveal. The recommended charge rate at low temperature is 0.3C, which is almost identical to normal conditions.
i.e Take a 120 Ah Battery.
You would charge that at 3.6 amps for 10 hours.
Only when it is cold, batteries ‘resist’ charging so a short “school run” in winter won’t be enough to keep your battery fully charged. You may not notice it immediately but without a good run, you are losing charge.
I also did a little article on Jump starting a vehicle a while ago if you want to refresh your knowledge about the most basic of recovery..