I can't say that ‘Onion Pacific’ (1940 - de facto directed by Willard Bowsky) is one of the better Popeye cartoons ever produced - it’s definitely one of the more mediocre shorts of the series. I can say though, that the cartoon has a moment of inventive brilliance and great timing.
Popeye is pissed off among the wreckage of his train and the water tower.
He changes mood as he savours the thought of eating spinach - setting up the events to follow. I love this bit of character business that's absent from practically all of the other Popeye cartoons.
As a side note I’d like to point out that this more sophisticated stretch and squash chewing action was alien to the earlier Fleischer cartoons. Though I can't ID the animator, I suspect it was done by one of the west coast imports. Despite the above drawings looking strange, you can see how the animator took care to follow through with the shapes and construction of Popeye's head to make sure that the chewing action was well executed.
Popeye fuels up on spinach, mimicking the action of putting coal into the boiler furnace. He becomes a human engine, his arms caricaturing the action of a train’s drives shafts, building up internal stream and readying for a burst of energy.
… and finishes with something that can't possibly exist - a super locomotive cobbled together from wreckage. After he slaps on the nose of the train it reacts like a real piece of machinery and grounds it in reality - at least our perceived reality of what a real train would look and feel like rocking on its shock absorbers. That action puts a great finish to the super train construction, punctuating its completion and easing out of the building action. It sells the idea to the audience that Popeye's locomotive creation could actually exist.
I wonder if the super train is metaphor for penis size??