Thread: AC/Heater Heated Rear Window - Auto On?
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Old 10th March 2008, 20:32   #102 (permalink)
Pottsy
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Quote:
Originally Posted by mike20 View Post
I'm sorry I'm not sure that makes sense to me. Thats like saying turn all your lights and air con on and it'll lower emissions because the engine's working harder.
I do realise that the emissions are directly affected by the rate that the engine warms up but deliberately forcing the engine to work harder to achieve it seems a negative way of doing it.
It turns out that this rather odd auto-defrost is a rather brilliant eco device. The diesel is only efficient when it's hot, but it's so efficient that sometimes it may struggle to get hot. It could spend ages running luke warm and all that time using more fuel than it needs to, just for the sake of a short load to get it warm.

Notice how the heater load only comes on when it's cold outside and the engine is cold - just the conditions you need to warm the engine up quicker, not the windscreen.

Very clever.
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