MOTOR (YOU KILLED IT)

QUESTION: I have a 2004 Warlock with a MerCruiser 496 Mag that has 250 hours on it. I am the original owner. The raw water pump impeller was bad so I changed it. After that it still wasn't pumping water through the exhaust system to cool it.

The engine temperature would rapidly increase to 210 degrees and then to 230 degrees after turning the engine off to check the water pump and for clogged passage lines. Now, the engine will not crank over and my spark plugs have water condensation on them. How do I fix this problem?

ANSWER: The MerCruiser 496 Mag water pump has a brass housing that does not have wear plates. Because of this design, if you severely damage a water pump impeller, it is likely the housing also was damaged inside where the front edge of the impeller seals. This is especially the case if you have sucked up some sand, rocks or debris. The housing cannot be repaired.

Originally, the only option was to purchase a complete new raw water pump. Mercury now has a universal replacement housing that can be used with all of the accessories and pulley from your existing pump. In order for the impeller to draw water, it also must seal on the ends. If the housing or backplate is scored, the impeller will not seal and no cooling water will flow.

When you start your motor after servicing the water pump, it is absolutely necessary to insure that water is flowing from the exhaust. If water is not flowing out of the exhaust tips, there is no cooling water and damage is eminent. Your engine is equipped with a closed cooling system. The engine coolant is cooled in a heat exchanger that raw water flows through. This exchanger functions the same as a radiator in a car. The reason the engine ran for a little bit and then overheated is because it takes a little longer to heat up the coolant in the engine. If your engine coolant was as high as 230 degrees, I hate to think how hot the exhaust manifolds and risers were.

It is likely that you got the engine so hot that you have damaged the exhaust manifolds, risers or the gaskets between them. This could be a source of the water in your cylinders. It is also possible that you have a cracked head or damaged head gaskets. If this is the case, you will see a drop in the coolant level in the reservoir. If your exhaust tips are under water when the boat is at rest, it is possible that water was drawn up the exhaust and into the cylinders as the air cooled and contracted.

The best thing you can do now is try to get the engine running so you can assess the damage. Leave the spark plugs out and fill the cylinders with WD-40 or a similar penetrating fluid. Let it sit for a day or so to dissolve some of the rust and corrosion from the cylinder walls and pistons. Then get a large half-inch ratchet and a three-quarter-inch socket and try to turn the engine over by hand with the spark plugs out. Do not use the starter motor because you could damage it as well as the flywheel ring gear.

Once the engine is broken free, rotate it several times using the starter motor with the spark plugs out to evacuate all of the penetrating oil from the cylinders. Failure to do this could result in a hydraulic condition, which will bend a connecting rod.

Remove the exhaust manifolds and risers. Pressure check the exhaust manifolds using water to ensure they have not developed any leaks. Check the risers for leaks and replace the manifold to the riser gaskets. Replace the raw water pump and check for any pieces of the old impeller or other debris in the cooling passages.

It is best to back flush the system with a garden hose to wash out impeller pieces that might be lodged in the heat exchangers. Install new spark plugs and start the engine with the boat connected to a garden hose.

Make sure that water is flowing from the exhaust and the engine is not overheating. Let the engine run for an extended period of time while you are continually checking for problems.

FIX THE CAUSE, NOT THE EFFECT

QUESTION: I have a 2001 Eliminator Daytona with twin HP500s. It has remote seawater pickups in the sponsons under each motor.

During the five years I have owned the boat, I've replaced the water pump at least three times a year. All the pumps have been on the starboard motor except one. Of course, the starboard motor's pump is hard to get to. Last spring, after replacing the starboard pump, I couldn't get any water flow. I took apart the feed line hose to the sea strainer and found "just the right size" clamshell jammed in the hose. I think it would open like a valve most times, then pivot closed, shut off the water flow and cause damage to the water pump. The shell may have been in the hose for a number of years.

In addition, many times I have damaged a pump when taking the boat out of the water. When the boat is on the trailer, the seawater pickup sits atop a support slat and is covered. I imagine the slat needs to extend beyond the end of the hull for support so I'm afraid to cut it short. Last week, the starboard pump again went out as I was loading the boat on the trailer. I'm getting tired of replacing it.

Are there any alternatives to the stock pump? Is there one that can be run dry without damaging it? Are there any electric pump options that I could relocate in a place that is more accessible?

ANSWER: Your basic problem is that you are running your raw-water pumps without adequate (if any) water. When you burn up an impeller, the heat created can also damage the wear plates and the pump housing. It is possible that just replacing an impeller is not enough, which explains why the pump would not draw water after it was repaired. It is important for the rubber impeller to seal on the ends against the wear plates and housing (one-piece housing). If a seal is not created, air can pass by the end of the impeller, which prevents the pump from drawing water.

Fix your trailer. This is your primary problem. You can't continue to have your water pickups sitting on your trailer bunks. If you want to run your boat on the trailer, and have no other way of attaching a garden hose, you need access to the pickups. It is true that your trailer should fully support your boat in order to prevent a hook from forming in your sponsons.

You'll probably need to add another cross member to the trailer in the rear in order to support another bunk stanchion. By doing this, you can have a break in the bunk at the location where the water pickup is in the sponson. Then you will have a short section of bunk in the trailer aft of the pickup. Many trailers are built with a break in the bunks for using travel lift slings. The concept for your trailer will be similar. The bottom line is that this modification can be done for a lot less than the number of water pumps you have purchased. And you will be fixing the cause, instead of continually fixing the effect.

—Need some guidance from Bob Teague, Powerboat's lead test driver and owner of Teague Custom Marine? To send him an email click here.

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