Have had a dozen or so Rangers/Explorers. Never had a problem with cracked heads. Hell, I was swapping a 302 in place of the 2.8 V-6 in my one Ranger. Pulled the drain plug out of the pan and fired it up. Took 30 minutes to lock up. Let it cool off, fired it up. Took 15 minutes for it to lock up this time. Next fire up I had to hold it floored just to keep it running. I gave it to the shop that built my 302. Steve polished the crank with some crocus clothe, resized the rods and ran the ball hone down the cylinders. I started working for him....the delivery truck had my old motor in it. Drove it like I stole it. He put well over another 100k on...it had 110k on it when I tortured it.