Discussion
This is a quote on another forum from some science bod ( ill have to change my ways)
No. You should depart immediately, but slowly. This is true for both diesel and petrol engines.
Idling a cold engine and waiting to warm-up before departing reduces the engine life. Why? Precisely because the engine shouldn’t run cold. Let me explain.
When idling at, say, 750 rpm, the engine warms up very slowly, especially if the engine is diesel. It will take, say, 15 minutes of idling to warm up. 15 × 750 = 11,250 revolutions. This means that all of the moving components made 11,250 cold, component-wearing revolutions.
If you depart immediately but slowly and drive at, say, 1500 rpm, the engine will reach proper temperature much sooner, after only, say, 5 minutes. 5 × 1500 = 7,500 revolutions. This means that all of the moving components made only 7,500 cold, component-wearing revolutions.
If you depart immediately and aggressively, the engine will heat-up even sooner, making even less revolutions cold, but the load on the components will offset the quick warm-up benefits.
Counter-intuitively, the colder the weather, the more damaging idle warming is: the already long idle warm-up time is even longer. So, in winter, it is even more important to depart immediately but slowly.
So, if we we order the start-up styles from the most damaging to the least damaging:
1. Cold engine, aggressive start (most damaging)
2. Cold engine, waiting to warm-up while idling (moderately damaging)
3. Cold engine, immediate slow departure (least damaging).
I understand this is counter-intuitive (many things about cars are!), but if you really think about it makes perfect sense.
No. You should depart immediately, but slowly. This is true for both diesel and petrol engines.
Idling a cold engine and waiting to warm-up before departing reduces the engine life. Why? Precisely because the engine shouldn’t run cold. Let me explain.
When idling at, say, 750 rpm, the engine warms up very slowly, especially if the engine is diesel. It will take, say, 15 minutes of idling to warm up. 15 × 750 = 11,250 revolutions. This means that all of the moving components made 11,250 cold, component-wearing revolutions.
If you depart immediately but slowly and drive at, say, 1500 rpm, the engine will reach proper temperature much sooner, after only, say, 5 minutes. 5 × 1500 = 7,500 revolutions. This means that all of the moving components made only 7,500 cold, component-wearing revolutions.
If you depart immediately and aggressively, the engine will heat-up even sooner, making even less revolutions cold, but the load on the components will offset the quick warm-up benefits.
Counter-intuitively, the colder the weather, the more damaging idle warming is: the already long idle warm-up time is even longer. So, in winter, it is even more important to depart immediately but slowly.
So, if we we order the start-up styles from the most damaging to the least damaging:
1. Cold engine, aggressive start (most damaging)
2. Cold engine, waiting to warm-up while idling (moderately damaging)
3. Cold engine, immediate slow departure (least damaging).
I understand this is counter-intuitive (many things about cars are!), but if you really think about it makes perfect sense.
smashy said:
1. Cold engine, aggressive start (most damaging)
2. Cold engine, waiting to warm-up while idling (moderately damaging)
3. Cold engine, immediate slow departure (least damaging).
While I largely agree with this summary you also have to consider the torque demands you're putting on the engine.2. Cold engine, waiting to warm-up while idling (moderately damaging)
3. Cold engine, immediate slow departure (least damaging).
For example, if you live at the bottom of a large hill, it's all well and good suggesting you stay under x rpm while the engine in warming up, but if this at the cost of having to use more throttle to generate the torque needed to maintain speed/accelerate uphill, you risk damaging the engine this way as well.
akkers5 said:
Convention wisdom says that when you start a diesel car from cold, you have to let it run idle for a few minutes before driving off. However, the BMW manual says the opposite - drive away immediately after starting.
I'll follow the manual but anny opinions?
Conventional wisdom has said for decades, start and drive straight away. Applies to petrol or diesel. The only reason not to is if it has piss poor air con/ventilation and the windscreen gets misted with your breath. The windscreen and exterior should have been de-iced/cleared before starting if needed.I'll follow the manual but anny opinions?
Brainpox said:
smashy said:
1. Cold engine, aggressive start (most damaging)
2. Cold engine, waiting to warm-up while idling (moderately damaging)
3. Cold engine, immediate slow departure (least damaging).
While I largely agree with this summary you also have to consider the torque demands you're putting on the engine.2. Cold engine, waiting to warm-up while idling (moderately damaging)
3. Cold engine, immediate slow departure (least damaging).
For example, if you live at the bottom of a large hill, it's all well and good suggesting you stay under x rpm while the engine in warming up, but if this at the cost of having to use more throttle to generate the torque needed to maintain speed/accelerate uphill, you risk damaging the engine this way as well.
akkers5 said:
Does it matter if your car has a turbo? Do you need to let turbo get warm?
No. Just start and drive off gently, as with any other vehicle. (Nearly every petrol and diesel engine has a turbo today, and I would put money on all their handbooks saying drive off gently straight away)Edited by Pica-Pica on Thursday 7th February 20:05
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