[aronpye]

I used to help develop Diesel Engines before I moved into Software Engineering.

If they followed anything like what we did, they would just run load cycles on the engine in a test cell to simulate approximately however many miles of ‘normal’ use they want to validate the engine up to. During the testing the engine would be maintained, fueled, and oiled according to the maintenance schedule and customer guidelines the engine will be sold with.

After the testing, the engine would be completely broken down and analyzed. If there weren’t any signs of abnormal wear then the engine would be considered validated __under those conditions__.

The problem is when real-world use deviates from the testing conditions. Which is pretty much always. Then the manufacturer guidelines no longer apply.

If you run your engine harder than the test cycle load factor, you will need to replace the engine oil more regularly. If your fuel quality is crap, i.e. has any ethanol in it, you will need to replace your oil more regularly as fuel eventually gets into the oil, and ethanol results in high water content in fuels, and hence oil, which will break down seals as well as reduce overall lubrication.

If your engine breaks down due to poor oil quality from lack of regular inspection and replacement, then as a manufacturer I’d be very resistant to paying out on any warranty claim. Even if you followed the “guidelines” for oil changes, you still have a duty to inspect the oil regularly, both as a responsible driver and under the car manual guidelines. Using bad oil and / or fuel is very easy to test for.

Long story short, the oil change intervals guidelines are just that, guidelines, and real-world use dictates the maintenance schedule. Frequent oil changes, before the oil breaks down / becomes crap, is just a quick, cheap way to prolong the life of your engine or any mechanical device with bearings or sliding surfaces for that matter.

[Dah00n]

>If your fuel quality is crap, i.e. has any ethanol in it, you will need to replace your oil more regularly

That is real-world use in most of Europe and is included in the higher mileage between oil changes compared to the US discussed here. I don't even think most Europeans inside the EU have access to ethanol free petrol? At least around here (Denmark) it would be illegal. If a car breaks down because of ethanol in the petrol it is of course covered by the manufacturer. Otherwise they might as well state "warranty 5 years but not if petrol has been added at any point".

The manufacturer specified intervals are just fine and you'd need to be an extreme outlier to have any problems with your oil following them. Maybe if you have a caravan attached at all times or drive off-road or racing or all of the above at the same time. Otherwise consumer law would mandate the manufacturer pay for any damages caused, as it damn well should. It is also the manufacturer that would have to prove the fault is yours. Not possible if the car have been serviced even if done by a third-party shop. The oil would have to be visible damaged even if looked at by a granny (they cannot demand you understand oil better than "it looks like oil and is inside the specified mileage").

[chrisseaton]

> Even if you followed the “guidelines” for oil changes, you still have a duty to inspect the oil regularly, both as a responsible driver and under the car manual guidelines.

No this isn’t true. I check my oil as regularly as the manual tells me to, which is every two years. That’s literally the published inspection schedule in the UK for this car. If that isn’t regular enough and the engine wears that’s a warranty issue covered by the manufacturer.

[aronpye]

Most manuals tell you to inspect the oil monthly or before a long car journey.

Waiting two years before realizing your engine is drinking oil is probably reckless which wouldn’t be covered under any warranty.