If the water was not touching the temp probe of the gauge, the gauge will read cold. The probe will only read water, steam or hot air will not make it read. Chances are, the engine was low on coolant, then over heated and locked the t-stat open. I have seen bus engines so hot the water was boiling in the block for 7 to 10 minutes and still read cool to normal temperatures on the gauge.
You would have to have one really bad rear main to go all at once like yours did. It could happen, but unlikely. Turning the oil pump with a drill will tell you pretty quick like Don suggests. Use some spray brake cleaner to really dry out the area before starting.
Don't go working on the side of the road, rear mains can be pain and should be done very carefully so you don't have the same problem later on.
Joe
