Having just bought a Skoda Superb, I note that, with variable service interval cars the recommendation is for one particular oil type which should not be mixed with other oils. I had diesels before and always used 'Prolong' oil additive which is the super slippy stuff which treats the metal bearing surfaces and prevents wear (so they claim).

If this is used in variable length service interval engines which have an oil sensor which determines the oil quality by measuring resistance of the oil, will it upset this device?

I've used this before in SEAT leon 1.9 TD 110(PD) without problems. Anyone have any knowledge on this?

Don't waste your money on these oil additives. Modern quality oils are all you require these days.

i wouldnt use any additives in the engine...previous issues when my dad put some in his engine...the oil pick up pipe strainer became blocked....eventually siezed the head and stripped the belt...stick to the modern specified oils, and for good measure change th oil more frequently compared to the dealer specifications.

In my opinion, you'll ignore that advice only at your peril.