Audi A5 Forum & Audi S5 Forum banner
1 - 1 of 18 Posts

· Registered
2,046 Posts
I would have thought that when it's colder your car will have better performance as its getting cold air through the intake.

One for the prof I believe.
Someone called? ;)

OK... I'm a petrol head, not diesel head, but here's my view...

I petrol cars, the colder the air, the more dense, which boosts compression by a few percent. Cold air frequently has a high moisture content (at least here in the UK) which is incompressible, also boosting compression.

However, in a diesel, I would expect the following:

Diesels run much higher compression ratios (15 to 25:1), so the additional air density should make a difference, but the extra damp and cold will affect the diesel timing (something that can't be controlled precisely) and almost certainly alleviate this.

Diesel fuel also needs to be injected a ludicrously high pressures >1,000 bar. at lower temperatures, the fuel starts to become more viscous and I expect injector performance will decrease and acheivable rail pressures to be reduced. This I expect will lead to the reduced performance you are seeing.

...just an educated guess though!

Cheer, Prof. :)
1 - 1 of 18 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.