Expert: Mike Evans - 11/3/2009

Question
will a 1991 mazda navajo 4.0 engine fit in a 1995 Mercury mountaineer ....it had a v8 engine in it.

Answer
    It could be done in theory, but it would be a huge job.  Plus, the '95 has an OBDII system and the '91 doesn't, so none of the electronics would work.  Even if you were given a low-mileage '91 for free it would probably cost more than just putting the right engine back in.  I had a V8 Mountaineer and after I drove a V6 Explorer I had to get out and look for where they had tied on the anchor chain.  There is way more than a 25% difference in power and torque.  The 4.0 is really just a stroked-out 2.9, anyway.  After you fix the engine in the Mountaineer, go and get bigger front and rear sway bars.  You will not believe the difference it makes in the handling, especially if it's all wheel drive.