Your statement makes me wonder why we have such different experience on oil change. I had a couple of Chevy’s back then, and I poured in the said oil amount, and the oil level would always be at the Top / Full mark of the dipstick. As I mentioned earlier, even today, I put in the said oil amount in the manual on newer vehicles, it reaches the Max / Full mark of the dipstick all the time. The only exception is my Mazda CX-5. It’s off by almost 0.5 quart! This isn’t just on my 2.5L NA, but also on the 2.0L and the 2.5T. The spec says 5.1 quarts for the 2.5T, but most find it needs at least 5.5 quarts to the Max / Full mark.
In addition, Mazda manual says the rear differential needs 0.48 quart (or 0.37 quart for 2nd Gen CX-5), but in reality it needs about 0.75 quart to fill to the brim of the fill hole! This’s the “approximate” fluid quantity listed in the manual to its max I’ve ever seen!
It can be the personal preference not to fill the fluid to the maximum level. But I always consider the more important “safety margin”. In fact that’s why almost every car manufacture set a fluid capacity to the maximum amount. My personal experience where my 2018 Toyota Yaris iA overfilled as usual by the dealer from Toyota’s new vehicle free maintenance actually saved my engine. The slow leak from the drain plug after the oil change and the long road trip from San Jose to LA, where the engine lost more than 2 quarts along the way without any warning! Had the dealer didn’t overfill the oil, I firmly believe the low oil pressure warning light would be on and we’d get stranded on the road, with engine damage by oil starvation!
My 2016 CX-5 consume some oil since new, and I want the oil level in full after each oil change to have a better safety margin, and avoid oil top-off before the next oil change.
Of course oil overfill isn’t good. But we’re talking about getting the oil in full, not over the full mark.
Oil dilution by fuel could happen but very rare. Here in this forum I’ve only seen a couple of reports in many years. Of course the Mazda’s 2.2L diesel is a different story, especially in early years.