If you own a Ford E350 or E450 with the Triton V10 or the smaller Triton V8 engine, you have the 2-valve version that offers less horse power than the 3-valve version. You have 2-valves because the 3-valve version is too large to physically fit in the van's engine compartment.
I was thinking of buying a used Ford F150 4x4 pick-up truck, a 2006 with 105,000 miles which had the 3-valve 5.4L-V8 Triton engine. I got on an F150 forum and asked a general question on what to inspect for, and I got a boat load of information, specifically concerning the engine. I also have a long time friend who has worked for decades as a tech for an area Ford dealership. His advise was plain and simple. Do NOT buy a Ford pickup truck with a 3-valve Triton engine.
If you are tech-savy and enjoy a "good watch" on engine stuff, the two videos in reply #7 in my posting question
HERE are fascinating. The videos point out clear evidence that the engine heads get damaged over the miles due to oil starvation that first shows up on the right head. The problem is accelerated when people don't change the oil frequently enough to prevent engine sludge formation.
What I took from this is a warning to us here is to change your oil every 5000 miles. Don't go longer.Better to be safe than sorry. Going longer will build up engine sludge. Some of the oil passages on the 3-valve engine (and maybe also on our 2-valve versions) are smaller than usual and they clog very easy. So changing your oil at 5000 mile intervals will prevent sludge build-up and keep those tiny oil passages clear of obstruction.