Somewhat related but if you ever attended Raptor Assault, they talk about driving the truck through mud/water and we were cautioned to not "plunge" into the water/mud mixture because it will get on all parts under the hood including the fan belts and fan motor. They said they will know if someone has done this because their truck will squeal.
That being said, we did get the trucks real dirty, just didn't plunge into the mix at any high speed or go into any deep puddles.