My favorite overlanding truck engines as a master tech:
Ford 7.3 diesel. 98-2003 forged crank versions. All of it's bugs were an easy fix, just don't let the oil pan rust. Too bad the 4 speed Trans was a bit anemic. A modern '17 6r100g would have made that the best truck engine of all time.
Jeep 4.0l. Easy to fix fuel injection. Super reliable. No Jeep engine since has even come close.
Ford 4.6. 2 valve in F150's or Econoline's. All the power a 150 needs. Too weak to Grenade itself. Predates all of the spark plug nonsense.
GM ZZ 383. Yeah, it's a carb'd crate engine. Deal with it. Simple is good. Last time I loved GM anything......it had a carb.
GM 8.1. It drinks oil. So what? It's one of the most reliable engines out there.
Ford 6.2. The engine Ford should have made 20 years ago. Torque via transmission, not from long stroke crap like the 5.4l.
V10. Both the Ram and Ford (2v) V10's were relatively trouble free. Get some double insulated plug wires for the Ram.
GM 6.0. Too weak to hurt itself. One of the most reliable engines that I ever hated, in the absolutely worst trucks that I've ever driven. One ton trucks and Russian quality Express vans.
Mercedes I6 diesel. In junk yards everywhere. Best crawler engine you can get for $350. Every time somebody swaps a Cummins into something smallish, I pitty all of the poor junkyard Mercedez diesels waiting for their forever homes.
Toyota 5.7l. Once you get past the fact that you have to tear the engine apart for a minor starter replacement. And abysmal fuel economy.
Suzuki Drz400s. What happens when you decide to build a cheap reliable 4 stroke dirtbike engine, instead of a high maintenance race engine......you get the most reliable 35hp engine of all time.
Popular overlanding engines that I disapprove of:
Jeep 3.6, 3.8. Way too many sob stories, and lunched cams. Heck, any Jeep engine before or after the 4.0l. Ha.
Ram Hemi. Cams, rockers, same issues as Jeeps.
Ford 300 I6. God I hate this leaky water pump, frozen tstat, freeze plug throwing menace. Whatever made this engine a favorite of the Grey haired Olde timers, was long gone by the time I started working.
GM Duramax. Backwards head gaskets and all of the same fuel pump issues that Ford and Dodge have. But it always get a free pass. That's what annoys me the most. "My Duramax has been perfectly reliable after $14,000 in repairs in just 80k miles. Best truck ever.''. Lol, yeah OK.
Anything with a Bosch Cp4 fuel pump. The big three need to pull their heads out of their arse, and get this fixed. You can't keep charging people $12,000 to $18,000 for what a diesel shop can fix for $4000. I'd avoid diesels at all cost, unless you have no choice. Often, it's just one stuck injector dropping rail pressure too low to start the engine. But the dealers replace EVERYTHING because they, and their brand, are incompetent. It's not just bad parts, it's some pretty simple bad engineering. Sadly, it's not rocket science to figure out how to get rid of these issues. Just that all 3 brands have failed to address it.
Mercedes 3.0l Sprinter van. Actually a nice engine, when it isn't eating your wallet. Sprinter fans are hardcore about service records and keeping receipts for engine upgrades for a darn good reason.
GM Iron Duke. 3.0l by now. I think it started off at 2.2 or something. Starter isn't key'd to the flywheel housing, all starting torque is transferred directly into the starter bolts. That snap like a twig. You can actually see the starter flex while cranking. GM 5.0, 5.7, 4.3, and the Chinese copies of those and the 6.2 have same issues 40 long years later. Some manufacturers just never learn, or plain don't care. Next time that I see this in a boat of piece of heavy equipment, I'm putting a pickaxe through the side of the block so that I don't have to drill out those bolts ever again.