Which American Engine Will Last The Longest

Assuming they are all mechanically sound from the start and similar miles, GM will outlast the Fords.
 
I would reluctantly say that the Marquis would soldier on longest, but I would probably grab the LaCrosse, sell the others, and use the cash to repair, clean, replace everything, detail, attend to dings and rust and drive off into this great land of ours in the Buick. Hope this helps. Everything on your list can deliver six figures more mileage in all odds, but the Buick is the comfortable one, handles properly.
 
The 351W ain't that great, but '96 was better. I don't know if machining tolerances improved or it was the release of the roller cam in '94, but those years could make it further.

I had a '90 351 and at 180k it was leaking oil from EVERY gasket and looked like PigPen driving down the road. I mean EVERY gasket from valve cover to front and rear crank seals and everything else. #7 was a dead hole with around 50psi and the others were barely above 100. But technically it ran "well enough"
 
Also I think most 2V Tritons are cruising around with broken timing chain guides but ignorance is bliss. If you did a timing set I'd say the 4.6 for sure. I realize this might be cheating, but I think the timing set is what will eventually bring the motor to its knees.

Pull the oil pan if you're ever curious....
 
As far as frequency of problems, I'd say they are all pretty much equal.

I'll give the nod to the pushrod V6s for ease/low cost of repair. No real PITA jobs on the 3.8 and 4.3. Timing set and exhaust manifolds are no fun on the 4.6.
 
The Ford 4.9l AKA 300-6 was excellent, but it did have a couple problems. If they were over-revved they would break the piston skirts. Amazingly they would run a real long time with broken piston skirts, I bought one that was knocking like crazy under load when I was a kid but ran for many years after. I eventually rebuilt it and the skirt pieces were still in the oil pan for 2 cylinders and the walls were scored pretty good, but a 0.030 ovebore cured it.

The later years also used a fiber timing gear that would fail. However it was not an interference engine so it was an easy fix - replace the gears.
https://www.summitracing.com/search...K7tGqpSDuabCD8TnxELpn5SUUMccFfxGAL8w-p6X8MjBx

plenty of aftermarket choices to fix this.
 
Also I think most 2V Tritons are cruising around with broken timing chain guides but ignorance is bliss. If you did a timing set I'd say the 4.6 for sure. I realize this might be cheating, but I think the timing set is what will eventually bring the motor to its knees.

Pull the oil pan if you're ever curious....
Was not an issue in the 2Vs, you are thinking of the 3V.
 
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