Don't know anything about Jasper engines, but....
Mrs. Mush had an 07 Explorer V6 Eddie Bauer from 07 till 15, and we put about 109,000 on it. The cooling system on that variation of the 4.0 V6 is badly designed. I went through 4 radiators and 4 or 5 thermostat housings/water outlet plastic conglomeration things in our last 3 years with that truck. It's not uncommon to just always have a small coolant leak on those engines when they get over ~90,000. Since I had one I pay attention to it when I see them in parking lots and probably half the time I can smell coolant when I walk past one. The common failure is in the plastic water outlet which leads to coolant leak into the V of the engine, where it evaporates and doesn't leave a puddle. On top of that, the heads are pretty prone to warping with even minor overheating, which will lead to head gasket failure and water in the cylinders. The small coolant induced intermittent misfire, and head gasket that was 12 man hours and $500 worth of special tools was the death knell for our Explorer.
While I didn't experience it, the 4.0 SOHC is also pretty notorious for timing chain and guide issues in the 45k-60k range.
Those issues are with Factory parts under OEM assembly. Rebuilt only gets worse.
For my money I'd get the 4th Gen Explorer with the 4.6 Mod V8 (which is nigh on bullet proof) or jump to the 5th gen with the Ecoboost or Duratec.
Just my $.02