Knocking Noise on Cold Start-Ups

[Moosh]

I have an Audi V6 2.6 convertible 1996 72,000m. When cold I can hear a knocking sound from the engine, but when it warms the noise stops. Any idea’s what this might be

[_Batty_]

Tappets?
get them checked/adjusted. do you know if they are hydraulic?

[Moosh]

Sounds to loud for tappets, and why would the noise go when the engine is warm

[Robatr0n]

As the oil gets warmer it thins down so the result is tappets go quiet.

Try changing grade of oil, but perhaps the best bit would be to invest in some new cam followers (tappets).

[Moosh]

I still think the sound if far to loud to be tappets but I will check

[Robatr0n]

Its suprising just how loud they can sound when they are getting old and knackered.

[Moosh]

Wouldn’t the tappets be a more even knocking noise, the knocking I can hear is uneven and lasts for only a few mins.

[speedtwelve]

Don't know about the Audi V6, but the VW VR6 engines can suffer from piston slap when started from cold. It's almost a thudding/clonking noise, much beefier than noisy hydraulic tappets. Might be that.

[Moosh]

This sounds more likely, anything to worry about?

[speedtwelve]

Sorry Moosh, been away for a while with work.

Opinion on piston slap seems to be that if it goes away with the engine warmed-up then it's not much to worry about. It's caused by too much clearance between pistons and bores when cold. Having said that, the engine on my Corrado was rebuilt (with previous owner) at 60k miles due to excessive piston slap; the pistons whacking the cylinder walls had caused enough damage that a rebore and oversized pistons were required.

Not kicking the $hit out of the car from cold is a good plan for longevity. I don't use more than 3000 rpm and part-throttle until I have an oil temp of 80C. I know there are some owners who won't even go as far as 3000 revs until warm.