idle ticking sound near start-up

Does anyone know what causes the engine to make a ticking sound when idling for a bit after it's been started cold? My friend's Passat does this. The length of the ticking period is generally short, although a while back when it was colder it seemed louder and longer.

Tappets, rockers lifters etc, I think it's fairly common on tdi cars, maybe need some better oil.

+1 on the lifters.

Try putting some additive in the fuel. The ticking could be from oscillations from some uncontrolled fuel burning.

Seatman said:

Tappets, rockers lifters etc, I think it's fairly common on tdi cars, maybe need some better oil.

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Well, it is a new 2012 car, so I doubt the oil isn't the right kind.

Seatman said:

uncontrolled fuel burning.

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Uncontrolled fuel burning?

oxford_guy said:

Uncontrolled fuel burning?

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Fuel insufficient in cetane is more unpredicatable when it burns inside a diesel cylinder and sometimes you get more than one flame front. When it does that, high frequency oscillations are set up inside that can sound like metal hitting. When two metal object hit, they oscillate. That is why they make a "tink" noise.