What does it mean when a car is "hydrolocked"? Is there any way to fix it? --- Bob, Madison, WI
Marshall Brain Answered:
An engine gets hydrolocked when it breathes water rather than air. This usually happens then the car drives into a pond, lake or river with the engine running, or when there is a huge puddle on the road. This would be a classic hydrolock situation:
Once a cylinder fills with water, the compression stroke jams or "locks" the engine (because water does not compress) and the engine cannot spin.
It is getting harder to resurrect cars that fall into lakes because there are now so many computers, electric motors, airbags and electronics that don't handle wetness very well. But on older cars, as long as nothing gets bent when the engine locks, it is usually possible to get rid of the water and dry the engine out as shown here:
Basically you pull off the intake manifold and dry out the whole intake path, pull the plugs to get the water out of the cylinders, pump the water out by cranking the engine, and then put everything back together.
You might wonder why you sometimes see 4-wheel-drive vehicles that can plow through water without hydrolocking. These cars have been waterproofed and use a snorkel like this: