Dear Tom and Ray:

I frequently cross a river as a shortcut to my farm. I have a 1996 Toyota Tacoma 4 by 4, and the water level reaches just below the doors. I can cross the river in about 15 seconds. My concern is that I could be doing harm by submerging the truck in water. I had all the fluids changed in the front and rear differentials and the transmission. The mechanic said no water was present. Is there anything else I should be worried about? -- Scott

RAY: Other than driving around with dead trout in your hubcaps? Yeah. I'd say your first concern should be hydro-locking the engine.

TOM: Hydro-locking is what happens when water gets sucked up into the engine's air intake. The water gets drawn into the cylinders, and when the pistons come up, the water doesn't compress like air does. So what happens is that the pistons, rods, valves and cylinder walls all combine to create an instant metal sculpture worth about $4,000.

RAY: And you'll know right away that you've hydro-locked the engine, because it will stop suddenly in the middle of the river and never make another sound.

TOM: We see this happen from time to time when a car goes through a deep puddle after some heavy rains, so a river is certainly capable of causing an engine to hydro-lock, especially when you factor in the wake you're making and the uneven nature of the riverbed.

RAY: The air intake on this truck is in the upper front corner of the engine bay, which is higher than it is in a lot of other vehicles. So in absolutely still water, with an absolutely flat riverbed, you'd probably be OK if you were moving very, very slowly. But you'd still have to worry about water getting in the vent holes of the front and rear axle assemblies and the manual transmission.

TOM: So if I were you, I'd take the long way to the farm. Or, if that's really inconvenient, spend the four grand on a nice bridge. At least that way you'll have a chance of making some money back by charging your neighbors a toll.