Here’s my take on trying to put this subject into perspective.
I have been told by a number of sources that in the U.K. that the recommendation is 4yrs or 80,000 miles ( 130,000. + Kms ).
I can believe that to virtually guarantee No Cambelt failure changing it at 80,000 miles on vehicles covering 20,000 miles/ yr is a no brainier £650+ verse £7,500+ for an engine rebuild.
Now the thing that concerns owners that own a Camper Conversion that does very low milage , sub 5,000 miles/ year, why should I have a Cambelt change every 4 yrs when I’ve only done less than 20,000 miles in that time.
Rubber and fibre Cambelts wear over time but remain flexible if used constantly, BUT what happens when these low milage vehicles are laid up for 6 months of the year with the belt in tension, in one position and still exposed to the atmospheric degradation common to all such rubber compounds. I very much doubt if any extended R&D has been carried out as the very low milage vehicles are a small % of the vast majority produced.
If you decided to ignore the time interval and just went with milage only, to replace the Cambelt then for the owners of these low milage vehicles it may take them 20 yrs to reach that milage and each year over 4 yrs the risk of a catastrophic Cambelt failure increases by “ x “. So it fails at 20yrs and you end up with a £7,500+ bill.
Changing it every 4 yrs in the meantime would have cost 4 x £650 = £2,600 or thereabouts and with each change, if done by VW you have 2 yrs warranty on parts and Labour + a virtually zero risk of a Cambelt failure.
So over 20 yrs and 80,000 miles your looking at £2,600 v £7,500 at present prices.
I have heard recently that some places are quoting 5 yrs or 80,000 miles.
I had my belt changed at 4 yrs AND 80,000 miles. My next will be done at 5 yrs and about 130,000 miles thanks to Covid 19.