A snorkel won't save your engine
I write this up because even though I read heaps of magazines and on the web I never came across this anywhere. It might save your engine...
A snorkel is supposed to keep the water out of your engine. And it does but only to a degree. Even if all your connections are perfectly water tight you might still inhale the wet stuff. How? Many air filter boxes have drainage holes to get moisture and bigger bits out again. If you just drive through water that shouldn't be a problem. I've been in over bonnet deep crossings a few times by now. But if you get bogged in deep water then your filter boxes will happily fill with water which the engine sucks further in. And we all know that's not a good thing.
I've also read many times to let your engine idle if you get stuck in water. I assume to keep water out of the exhaust and to keep higher voltage on the battery? I do wonder now if it would be better to switch off right away if stuck in bonnet deep water. Than at least the engine can't inhale the water which floods the filter box and all you need to do is dry out the filters or replace them once you're out. In addition it's a good idea to take the glow plugs out and turn the engine over just in case water did get in there (it will spit out the holes). Black engine oil alone is no indication that water didn't get in some parts of the engine. In any case I would temporarily block the drain holes before any deep water crossing.