im guessing its a head gasket, as this is the same thing that happened to me
did you see the markings on the head gaskets that said "front" on them? if they're turned around, water wont be able to flow properly
i know you said theres no coolant in the oil but it is sometimes hard to see, i couldnt tell by looking at the dipstick but i let the car sit then drained the oil to see about 1/2 gallon of pure coolant came out before ANY oil came out, i guess oil and water REALLY dont mix
good luck with it
------------------
88 Notch, B&M Ripper, 3.73's, Ported E7's, Explorer int. w/ ported lower, pulleys, 1.7RR's, BBK headers, off-road H-pipe, flowmasters, subframes, 65mm TB, March ram air ,MSD coil, U/L control arms, 155lph f/p, Crane Adj.FPR, Nitto drag radials, best 1/4--> 13.76@101.4 on a 2.17 60ft