@Drewmcg
Here's why I'm here now:
"The dealer told me coolant entered the engine when the water pump failed." I did not question this earlier, as I suspected something funny has gone on with water pumps. Hell, isn't the pump EXPECTED to cause water to enter the engine??
What exactly is this "fixed" pump all about, anyway? I just know, you know! Thanks! imp
Imp: Like you, I suspect (another Gen 3 Explorer owner), I like the idea of picking up a wounded used Ford SUV for a few bucks and bringing it back to life. I really do like my '02 Explorer XLS now that I've swapped in a lower-mileage used 4.0L engine and replaced the timing components.
I looked at late 2000's Ford Edges (generally positive consumer reviews)--smaller and not a truck, but somewhat more fuel efficient. I learned that Ford introduced the 3.5 transverse mounted duratec in 2007 Edge (I think) or Flex, with variable valve timing and slightly better mileage than our 4.0L colognes (owing in part to lighter vehicle weight, however).
As you know by now, to save space the engineers (at Mazda in Japan, I think, but I might be wrong) moved the water pump inside the timing cover, over the oil pan, and drove it off of the timing chain (instead of off the accessory belt used to drive power steering, A/C, etc. on our engines). The early design used a single row of teeth. I've read reports that the Japanese engines used in Mazda's variant had good specs for the water pump, but that the U.S. built ones used in Fords started experiencing significant failures, often soon after the 60k miles warranty expired. Basically, the shaft seal (?) failed and allowed coolant to leak through and drip down into the oll pan, diluting the oil overly a relatively short number of miles, decreasing lubricity, and causing bearings to fail and other awful things. This affected 3.5 and 3.7 Duratecs, but Ford sold a ton more of the former.
In approx. 2011 Ford's "fix" was to re-design the water pump slightly to use two rows of teeth instead of one row. There may be other, less visible, changes as well. This required that other timing components change, too (e.g., at double-row timing chain). While I've seen some reports of post-fix failures, they are not nearly as frequent. And, like the post above that I asked about, may not even represent a water pump failure at all (could just be a blown head gasket in that case).
For what its worth, I've read of one case where the owner of a 2007 Edge who caught the problem before it completely destroyed his engine ordering all of the post-fix components (including new water pump design, timing chain, gears) and successfully installing them on his SUV. That seems pretty cool to me.
I might eventually try to find a late-2000's Edge or Flex that still runs, where the owner caught the problem early, took it to a dealer and was told it is a $2-$3k repair, and decided sell rather than spend that kind of money. The two problems I see are: (i) its very hard to repair water pump/timing components with the engine in the car; and (ii) how would you really know whether the problem was caught early enough to avoid major engine damage?
Hope this answers your question.