This. There's something in that oil other than the oil itself. Takes minimal time to do a pressure check on the cooling system.
I've rebuilt engines that have sat in a corner of a garage for decades with a full sump of old oil, and while said oil was ancient it would still lubricate.
People...
This is my gut feeling also, maybe a fine crack in a head or block that just manifested. I wonder what pressure testing the cooling system would yield.
On any new rig, I change the oil at 1,000 miles to get any break-in swarf out, then at 5,000, and at every 5,000 from there. Easy to remember, and oil and filters are cheaper than a rebuild. Tire rotations, every 10,000. Again, easy to remember.
This has served me well.
That's it, although mine came with a green plastic dust cap and the hose barb you screw in to control the oil flow is also green plastic. Apparently those parts are optional now.
I've had both the Ronin and the Femco on my '19 F150. Either makes for a clean, controlled oil drain.
Anyone who owns or has changed oil on an F150 of this vintage with the 5.0 curses the existence of the engineer who put the front sway bar directly in the path of the drain oil. And with that...
Far better than a timing belt, especially one bathed in oil.
I see enough timing belt failures at work to know I don't want one driving a vehicle oil pump...
Great product, I have one on my '19 F150. Before it, I had a mini Exxon Valdez event each time I changed the oil in the damned thing with the factory plug. Now I don't spill a drop.
Truth.
I used to do some engine building on the side, and I have torn down engines that have sat in a garage corner on an old tire or stand literally for decades, some with a full sump (which is fun when you don't check and flip it over once on a stand), and I wouldn't hesitate to use said oil...