2000 Mercury V6 135-HP: Water Spray from Oil Tank Pressure Line

[GuardianRC]

Hi everyone. I've recently bought a 2000 Mercury 135HP V6 2.5 (single piece cover) and I'm doing a bit of digging before getting the boat in the water. The alarm was sounding continuously as soon as the ignition was switched on, but I fixed that by loosening the engine oil tank until oil flowed out with the engine running. I did notice that when checking for air pressure from the hose to the remote tank that there is a stream of air pressure, there is also a spray misting of water and moisture, which Is obviously not a good thing to be going toward the oil tank. I've not run the engine for more than a few minutes as the tell tale water isn't that strong.

Do you think [the spray misting of water and moisture going toward the oil tank] could just be condensation?

If [the spray misting of water and moisture going toward the oil tank is] not[ just condensation], how does the air pressure get accumulated?

Is [the accumulation of air pressure caused by] a pump"

Or something internal [in the outboard] engine which could have a rotted out waterway?

Thanks for any help,
Rich

[jimh]

Usually the positive pressure that is applied to the oil tank in a Mercury oil system is provided by crankcase pressure acting through a one-way check valve. For some background, read the REFERENCE article on the somewhat complex method used by Mercury to pressurize the remote oil reservoir tank; see

Mercury Automatic Oil-Gasoline Mixing System
http://continuouswave.com/whaler/reference/mercuryOilInjection.html

The article describes an older system, but I suspect that the same method was stil in use in c.2000.

[GuardianRC]

Thanks. I'm not as familiar with 2 stroke outboards as I could be, is there any likely way water can get into the crankcase?

[jimh]

...is there any likely way water can get into the crankcase?

In a two-stroke-power-cycle engine the "crankcase" is part of the fuel-air induction path, and the fuel air-mixture passes through the crankcase on its way to the intake port of the cylinder. You might find this illustration of the action of a two-stroke-power-cycle engine to be informative:

https://www.youtube.com/watch?v=viWhxvo6DLk

--or--

https://www.youtube.com/watch?v=P-WYdrRKQvs

Scroll into movie to 1:08.

Water vapor can be drawn into the crankcase from the atmosphere.

I don't understand how mechanism used by Mercury to generate positive pressure from the crankcase pulses for their oil system prevents the fuel-air mixture from being allowed to escape from the crankcase and into the oil tank. It would seem like positive pressure pulses from the crankcase would contain some fuel-air mixture.