4.6 Expedition high mileage

They are generally long lasting engines. Check to see if any smoke is coming out of the exhaust, ticks, knocks, also check the oil level and see if its full.

+1; that's the story I hear about them. I've seen guys on here with motors around 200K and no issue what so ever. Long as you take care of it, the 4.6 is bullet proof.

I have a 99 Expedition and now have about 160k + miles on it. No break downs yet.

Some of them have problems with the passenger headgasket leaking oil, besides that its the usual wear and tear of any vehicle.

take a small flashlight next time you go take a look at it. remove the oil cap and take a peek inside. it should be a light shade of brown, no black sludge. high oil change intervals will cause sludge that will hurt any engine no matter how bullitt-proof it is

check the ATF fluid, if it's the original fluid it will be brown with a slight hint of red (use a white paper towel or napkin). if it smells burnt or looks like strawberry milk don't buy it.

drive it and check for the obvious, smoke, knocks, wierd noises, etc. Ford trucks and modular engines in general are usually very reliable from what people who have owned them have told me

Most of the earlier (pre-'99) 4.6's were prone to valve guide seals hardening and leaking above 100k miles, or with general age. If you get a puff of blue smoke when you first start it, or if you sit at idle for awhile and then take off (or go WOT after cruising granny-like for awhile), that's usually an early indicator of this. It's not a terribly catastrohpic sort of thing, but it will cause you to go through a bit of oil over time, fouls out your plugs, and will carbon up your EGR passages; you can get away with running thicker oil, changing plugs more often, and cleaning your passages more frequently, but ultimately you'll wind up having to replace those seals, and it's NOT a fun project. Expect to spend around $600 or so to pay a mechanic to do it, or waste a whole weekend farting around with it, if you try it alone - also helps to have a compressor and fitting to keep the valves from dropping.

Also, if it has a plastic intake manifold, see if they're already replaced it with the updated design manifold that has the aluminum crossover. The stock plastic ones were notorious for cracking and spewing coolant without warning, until Ford came up with the revised intake. (Fleet vehicles were covered under the recall, but it may have already expired by now.) A new intake will run you around $250, plus misc. little stuff.

Otherwise, as mentioned above, the 4.6 is pretty much a bulletproof motor. I hate letting go of my 4.6 T-Bird tomorrow morning, as it's a helluva solid motor, but my budget can only afford gas for one V8 car at a time...