As someone who has successfully completed timing belt and water pump replacement on multiple first generation Miatas, I was confident as my son and I began doing so on his 1993 Mazda MX-5. We were following the steps of a detailed task list created from past experience. Using a kit purchased from RockAuto.com, we meticulously disassembled the necessary engine components and installed the new parts.

As anyone who has replaced a timing belt knows, care must be taken to ensure nothing is moved that will affect engine timing. Using the task list as a guide, I knew it would be practically fool-proof if the steps were carefully followed. Teeth were counted, cam and crank sprocket positions were noted, and everything was reassembled. The final step is to start the motor and celebrate success.

Except it didn't start. The engine would turn over but not fire. Not even a sputter. We reviewed the steps and confirmed nothing was missed. Using a helpful "no-start troubleshooting guide" available online, we spent the remainder of the day checking fuses, ignition, air, and fuel...even though I was doubtful something coincidental happened while we were doing the job. Nothing solved the problem, so we again removed the valve cover for a visual inspection. Everything looked OK. Exhausted and dejected, we called it a day so we could rest up and come back to it later.

Wracking my brain over what I had expected to be a straightforward job, I scoured an image of a 1.6L Miata engine with its valve cover off. Something didn't quite match up with what we saw in my son's Miata engine. Sure enough, the intake cam lobes were just a few degrees different from the photo! But how? We had counted and recounted the belt teeth. Back under the hood, we discovered that while reattaching the intake cam sprocket, it had somehow mis-aligned and rotated slightly relative to the cam. I didn't think that was possible, but there it was. After a quick remove/replace with proper cam alignment, the car fired right up and ran as smoothly as ever. A new step has been added to the work-list: double check cam sprocket alignment with the cam!

Eric in Washington

Hydrolock happens when enough liquid enters a cylinder to shrink the size of the combustion chamber. Gases are much easier to compress than liquids. During a compression stroke, the piston finds itself slamming against a hard wall of liquid rather than pushing against a relatively soft bubble of air and vaporized fuel. The liquid stops the piston, the piston's connecting rod stops the movement of the crankshaft, and the engine stalls.

Liquid stops the piston

Hydrolock happens most commonly when a vehicle is driven into water that is higher than the engine's air intake. To keep the air intake out of the water, serious off-road vehicles will often pull in air through a tall snorkel bolted to the A-pillar rather than an air box mounted down low behind the bumper as it is on many cars.

Excess fuel has become a more common cause of hydrolock as fuel pump pressures have increased over the years. A carbureted engine might have a mechanical fuel pump generating 5 psi. An electric fuel pump in the fuel tank might push out fuel at 50 psi. A direct-injected gasoline engine probably has an electromechanical fuel pump that can create a geyser of fuel at more than 2,000 psi.

With the higher fuel pressures, when a part fails it might only take a moment to fill the combustion chamber with fuel and hydrolock the engine. A ruptured fuel pressure regulator diaphragm could allow fuel to be sucked through the regulator's vacuum hose into the engine's air intake. The internal seals and plumbing that control flow through a fuel injector or direct-injection fuel pump might deteriorate and leak excess fuel directly into the air intake plenum or cylinder(s).

Oil or coolant can also hydrolock an engine if the piston rings are severely worn (oil) or the head gasket has a big leak (coolant). Help prevent fuel, oil or coolant hydrolock by watching for early signs of a leak. Excess fuel may wash past piston rings and get into the crankcase. The crankcase might become overfilled with a mixture of oil and fuel. Watch for blackish (fuel), bluish (oil) or whitish (coolant) smoke coming out of the tailpipe.

Keep engine rpm down to reduce the chance of damage to pistons, crankshaft, bearings, or other internal engine parts if hydrolock does occur. (Running into a wall hurts a lot more than walking into a wall.) Avoid gunning the engine in an attempt to speed through a water obstacle faster. Do not rev up the engine to try and blow out excess fuel, oil or coolant. Do not burn out the starter motor with repeated attempts to turn over a stalled and hydrolocked engine.

Clean out a hydrolocked engine as soon as possible. Water may cause corrosion. Fuel or coolant may contaminate engine oil and/or damage gaskets. Removing the spark plugs or fuel injectors (diesel) and manually cranking the engine is often the best way to get unwanted liquids out of cylinders. Replace the leaking/broken parts that caused the hydrolock; replace parts such as hoses, gaskets and filters that may have been ruined by exposure to incompatible liquids; and be sure to change engine oil that may have been contaminated.

Tom Taylor,
RockAuto.com

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