Rattling

[Cming]

Hello. I have V6 Tdi s tronic. When I excelrate there is a tinny rattling sound. It reminds of the old days when thr air file mixture was wrong for a petrol car. Please can you give me any ideas why it would be doing this

[cliffcoggin]

It's the same problem that you remember from the old days from your description: pinking or pre-ignition. It's the result of too weak a fuel mixture or a spark that's too far advanced or fuel of too low an octane rating. If you are using the right grade of fuel there is a problem with the engine that needs diagnosis.

[Cming]

Thank you for your Advice. Off the top of your head do you know what octane level the diesel should be? 

[cliffcoggin]

Diesel? You didn't mention diesel until now so I wrongly assumed the fuel was petrol.

Diesel does not suffer from pre-ignition so your problem lies elsewhere. Incidentally diesel, being a longer molecule, is measured by decane rating. As far as I know only one grade of diesel is available here, except for the anti-waxing additives in the winter.

[Cming]

Thanks sorry I didn't say it's diesel. 

Guess it's a diagnosis I will have to book it in for