Does old or new oil produce more power?

[xpensive]

To the best of my xperience, it's all about running temperature, which oxidates the oil and thereby ruin their lubricant properties?

[persovik]

How do the 18 wheelers here in the US get away with running their engine oils for so long? I'ver heard something along the lines of 75k miles. Is that true and if so how?

Some large trucks have secondary filtering systems installed where a small pump circulates the oil through an advanced ulta-fine filter.

[franz131]

To the best of my xperience, it's all about running temperature, which oxidates the oil and thereby ruin their lubricant properties?

True, Synthetic base oils are much more resistant to oxidization, enabling the long drain interval.

[Ray]

How do the 18 wheelers here in the US get away with running their engine oils for so long? I'ver heard something along the lines of 75k miles. Is that true and if so how?

Some large trucks have secondary filtering systems installed where a small pump circulates the oil through an advanced ulta-fine filter.

I knew about that, but those truck are not exactly the kindest on their parts. The engines are phenomenally strong and well engineered, but they have to abuse that oil temperature wise. At least I would think so.

[xpensive]

My xperience is that the issue is related both at local temperature peaks and the duration of the same. The latter can be in most cases be adjusted by having a huge oilsump. I can imagine local temperature peaks in an 18k F1 engine being phenomenal, but on an 18-wheeler, I don't know?

A local service circuit can be a very good idea to remove particles and even water at times, but does nothing to the oxidation of the lubricant, that's all down to the temperature.