Sorry for the bad grammar, I reversed a correction and really messed the whole sentence up. What can I say, it's midnight.
Well, you could conceivably get through water 48" high if you keep moving. The wake that causes a shallow in the rear of the vehicle could be enough to allow the proper ventalation. As for the engine sucking in water, that's only if the intake is below the surface and on a blazer it shouldn't be. Stop the vehicle in that high water and you have a problem. I have driven through tow to three foot water in a vehicle before, but make darn sure I didn't stop. I have also driven through 8 inches of water and had the misfortune of getting caught in a swell that went up to about four feet, swept me into a ravine. I was wet, and really pissed, LOL.
Most military vehicles have exhausts that are more than four feet high. Either on the hood, the roof, or high on the rear of the vehicle. This is specifically for fjording water. One thing you definitely don't want to do with a modern vehicle is go crashing through the water at a speed higher than about 5 mph. You will tear your fan apart and be stuck for sure.