Purpose Lower Unit oil reservoir?

[hostage]

I know until the early 90's Alpha One Mercrusier out drives didn't have a reservoir. I am curious about what the point of this reservoir is, is it just an alarm to let you know if there is a leak? If you have a leak will water have as equal amount of chance of coming in as the oil from the reservoir?

 

[09TNRT]

I've been curious about this as well, also wondered if water intrusion would show up in the oil in the reservoir.

 

[MBAKER]

my thought is...

It keeps the drive completely full of oil and yet allows it to breath as it gets hot sort of like the overflow on a cars radiator. Also, since the reservoir is higher gravity will apply a small amount of pressure on the system helping keep water out if you have a weak seal.

 

[TyeeMan]

I don't think water will trigger the alarm as I believe there is a float at the bottom of the container. Oil runs out, float drops, alarm.

A couple guesses, 1) to keep the drive totally full. There can be an air pocket at the top of the drive even if it is properly filled. From normal heating (expansion) and cooling (contraction) that air bubble gets pushed in to the reservoir and lube gets drawn back into the drive.

2) Perhaps it's easier on all the various seals. Prior models without the gear lube monitor were sealed tight. When they got hot even under normal conditions there was no place for the pressure and expanded lube to go. With the gear lube monitor any pressure/expanded gear lube gets pushed into the reservoir. Lube get's drawn back in when it's cool.

The same would apply in very cold temperatures. Only a vacuum would be generated. With the gear lube monitor there is less of a chance of sucking in water through any of the seals.

Just my .02

 

[alldodge]

The bottle is used as a visual reference to how full the drive is. The float inside allows sets an alarm when it drops, and does not detect water.

The bottle also has a one-way valve in the cap, which allows air in but not out. After filling the drive, the air pocket will work its way up into the bottle until its all out. The one-way valve keeps the lube under pressure as heat is generated and lube expands. There is not that much pressure but without the cap the lube will boil over and out the top. Once it cools down the lube will be low.

Being under a bit of pressure helps keep water out, but drive still needs to be drained an checked for water often. The ones without the bottle could leak and no one would have a clue until damage had happed or during maintenance.

Note, the bottle also needs maintenance, every 2 or 3 drains the bottle should be flushed out, cleaned and refilled.

 

[hostage]

The bottle is used as a visual reference to how full the drive is. The float inside allows sets an alarm when it drops, and does not detect water.

The bottle also has a one-way valve in the cap, which allows air in but not out. After filling the drive, the air pocket will work its way up into the bottle until its all out. The one-way valve keeps the lube under pressure as heat is generated and lube expands. There is not that much pressure but without the cap the lube will boil over and out the top. Once it cools down the lube will be low.

Being under a bit of pressure helps keep water out, but drive still needs to be drained an checked for water often. The ones without the bottle could leak and no one would have a clue until damage had happed or during maintenance.

Note, the bottle also needs maintenance, every 2 or 3 drains the bottle should be flushed out, cleaned and refilled.

The plastic transom fitting broke 2 years ago, granted I didn't use the boat for a year. I wonder if this is something I can put off a couple years, when I redo the bellows or is this something really critical that I should do it now?

 

[alldodge]

The plastic transom fitting broke 2 years ago, granted I didn't use the boat for a year. I wonder if this is something I can put off a couple years, when I redo the bellows or is this something really critical that I should do it now?

If the gimbal housing still has the quick connect and so does the drive, then it would be leaking lube into the boat or into the water and you would be running low real quick.

 

[hostage]

If the gimbal housing still has the quick connect and so does the drive, then it would be leaking lube into the boat or into the water and you would be running low real quick.

My mechanic replaced the barb on the lower unit with a plug then we plugged the hose in the boat to prevent water from coming in. Just wondering from any design aspects if doing this is bad. I think I will address the overall issue when I redo the bellows in a couple of years. The bellows are about 5 or 6, but I do store it in the down position over winter and they look fine.

 

[alldodge]

You should be good