[ron1004]

...any idea then how cylinders could have gotten filled with fuel on their own overnight?

Fuel injectors not shutting off good - fuel rail still has pressure when the engine is shut off, and that bleeds through the bad seating injectors into the cylinders.

 

[ron1004]

It's worldwide problem dealerships have, finding well qualified competent staff, in addition to modern vehicles have become fairly complex.

If Kia can prove that contaminated fuel caused the issue, there'll be no warranty cover.

We don't know what products are available in your location, but if you can find Techron it worth a try using it for a tank or two.

Techron Fuel Additive | Kia Forum (kia-forums.com)

 

[ron1004]

I didn't know that (involuntarily, of course) using contaminated fuel would not be covered by warranty.

That is standard the world over - your claim is with the supplier of contaminated fuel, not the vehicle manufacturer.

How would the user defend him/herself? Apart from refuelling from well-known dealers (in my case Q8, ENI, TotalERG, IP, ..., in this order of preference), what can one do?
I have a KASKO coverage for the first four years of life of the car, hope that would count—but mostly I hope this doesn't happen again.

It is always good practice to purchase fuel from reliable (well-known) sources.

No warranty provider is going to cover effects of contaminated fuel.

 

[ron1004]

• called another dealer, they told me they use the official one by KIA, and that I can buy it from them if I want

I will keep researching. Any feedback appreciated.

You've found a source for the fuel additive, and its been recommended that you only buy fuel from a trustworthy reliable source - what other feedback is there to offer?