Was fishing this last weekend with a friend in his boat and the engine beeper started going off. The engine had oil in the resevior mounted on the engine And water was coming out of the dishcharge hole on the side of the engine. This happened every time the engine was running. It finally stopped later in the afternoon. The cranking battery voltage was a little low but never caused the engine not to crank. Does anyone have any suggestions what the problem could have been?

What brand of engine and what was the pattern of the beeping?

+1 more info needed

The engine is a 200 Merc I believe its about a 98 model. The beeping noise was real fast pulsing noise. My buddy took the boat fishing today and he said it ran fine no problem with the beeper going of....could the voltage being low cause that? I always thought that the beeper was for either an overheating problem or an oiling problem.

Oil warning

Like Gary says. It's the oil sensor in the reservior under the cowling. The oil has dropped about 3/4" which makes the sensor react. Just fill the reservior by removing the cap and you'll be ready to go.

On my Merc it turned out to be a worn out plastic gear that drives the oil metering pump. The pump has a pump-speed sensor, and when the pump speed is not normal, it triggers the beeper.
Of course, this doesn't mean that a 98 has the same warning system as my 90.

Unfortunately Merc did away with that oil pump motion sensor. That IMHO was a great loss of a critical sensor.

This raises much curiousity. Does this mean that they also changed to a different/more durable method of driving the oil-metering pump? That plastic gear on the crankshaft is just too expensive to replace. After mine went out, and I learned all about this gear design, I felt there had to be a better way.
I loved the way it worked, and what it did, UNTIL it went out SSOOO prematurely.

Nope, Not really any change. Still a fiber material that will shear.

I have had the same problem on a 95 Mariner 175. Get in to rough water and the buzzer starts. My mechanic told me it was a common problem. The upper tank fills from the main tank and when it gets a little low, any movement on the water will cause the float to bounce and trip the alarm. He also indicated that when the engine is trimmed up and placed on a transom saver, the upper tank will often lower slightly by flowing back in to the main tank. Seems like a really poor design that was used for many years. I guess that is a good argument for removing the entire system and premixing by hand.

Actually your mechanic is almost right. The oil in the main reservior is under pressure, it will obsorb air. When the engine sets for an extended period of time, the pressure in both tanks relax allowing for the air to escape from the oil and henceforth begins an air pocket in the small reservior. The oil should not flow backwards as there is a check valve to prevent this.

My own research revealed to ME that there are more problems as a result of plastic gear failure, than there are due to float-sensor in the little tank. I was told several times that it was the float, that it saturates and partially sinks, or that the sensor fails. I replaced it twice, and NO CHANGE resulted. THAT'S when I learned about the internal pump gear business.
My engine came with TWO design deficiencies; the wrong propellor gearbox gear RATIO, and the plastic gear that drives the pump.
Mercury would do NOTHING about either.
Like a fool, I spent gobs of money on propellors. It wasn't until I spent $1,750 for a new 'foot' with the proper gear ratio that I was able to 'prop' my engine.
And, I manually mix oil and gas.
And, I'm being told that Evinrude is no better.
It ain't easy when you're faced with insufficent funds.