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Hi any know the part number as I need a new one

Hi Graham,

The expansion tank part number is - 4F0 121 407 A

Hope this helps.

Thanks I was looking for 4B3121321 the cap as mine is discoloured

If thats right one 4B312132 for the cap ? just looking on Ebay / Google for one

Apologies! I just scanned the title of the thread and missed the cap part!

Yes, 4B3 121 321 is the cap!

The blue colour has faded slightly on mines too! As has the green for the power steering fluid reservoir cap. I think the heat must have something to do with it as both caps on my diesel Skoda haven't faded anywhere near as badly!

I think I can recall that some people have fitted the expansion tank cap from the R8 on the RS 6 as they are the same fitment and I'm sure the R8 cap had silver through it just like our oil tank dipstick does.

I'll try and have a quick look to find the thread.

I can't find the thread, but the parts list for the R8 does list our part number - 4B3 121 321 (which is used on the RS 4, RS 5, RS 6 and R8) and also 420 121 321 which is specific to the R8. Looking that part number up online it does seem that people are using them on various VAG cars.

https://www.akstuning.co.uk/476-engine-bay-dress-up

You could always get a black one.