Mariner/Mercury 3.3 hp - gearbox oil change difficulty

[dunedin]

Got a new to me Mariner 3.3hp two-stroke - similar to our existing 2.5hp but with forward/neutral lever.

Just been trying to change the gearbox oil. Seemed to take a very long time to drain the old oil out but did so after 20 minutes or so (black but no signs of water).

Trying to refill the oil in the same was as used to do the 2.5hp - squeezing in from a tube using the bottom hole till runs out the top hop. However, there seems to be quite a bit of back pressure, so mainly just coming back round the edge of the nozzle - and not getting up to the top, which used to be easy enough (if slightly messy) on the 2.5hp.
Is there a trick or technique necessary for the 3.3hp due to the forward/ neutral lever? Or other ideas why the oil won't go back in and potential solutions.

Thanks

 

[VicS]

No reason why the 3,3 will be any more difficult to fill

Black oil should ring the alarm bells though
I guess with a "new to you " motor you will be fitting a new pump impeller so while the gearcase is removed tear it down, give it a good clean out, inspect the gears and bearings then reassemble with new seals.

 

[Seastoke]

Order a quicksilver gearbox filler about a tenner , I have just changed my Tohatsu 3.5 oil and that was black . Then to vics why should it not be black .

 

[dunedin]

No reason why the 3,3 will be any more difficult to fill

Black oil should ring the alarm bells though
I guess with a "new to you " motor you will be fitting a new pump impeller so while the gearcase is removed tear it down, give it a good clean out, inspect the gears and bearings then reassemble with new seals.

Why is black a concern? I thought any water ingress would make milky colour?

Good water flow so wasn’t planning to fiddle with the impeller. Not got my notes in front of me, but if I recall on the 2.5hp the impeller was just behind the prop anyway?
Being a visitor from Scuttlebut wasn’t planning to try to remove the gearbox as generally apply if it ain’t broke don’t break it by fiddling

Still struggling to understand what issue might make more difficult to get the oil to go in (with top screw also removed)

 

[dunedin]

Order a quicksilver gearbox filler about a tenner , I have just changed my Tohatsu 3.5 oil and that was black . Then to vics why should it not be black .

Is it this sort of thing ? Quicksilver 1 Litre Premium Gearbox GEARLUBE Oil & Pump Kit Tohatsu Outboard 1L | eBay
1L bottle would last me two or three lifetimes but if it saves an engineer bill would be worth it.
Currently using the Quicksilver tube which worked for the 2.5hp but not seeming to work for the 3.3hp.

 

[VicS]

Why is black a concern? I thought any water ingress would make milky colour?

Good water flow so wasn’t planning to fiddle with the impeller. Not got my notes in front of me, but if I recall on the 2.5hp the impeller was just behind the prop anyway?
Being a visitor from Scuttlebut wasn’t planning to try to remove the gearbox as generally apply if it ain’t broke don’t break it by fiddling

Still struggling to understand what issue might make more difficult to get the oil to go in (with top screw also removed)

If all is well the oil you drain should be "clear and bright" and no more than a little darker in colour than when new.
Black oil suggests to me that water has entered and caused corrosion of the bearings and gearbox internals. Hence my suggestion that it is dismantled cleaned and inspected and rebuilt with all new seals.
While it's off and stripped down it makes sense to fit a new impeller then you should not have to worry about it again for a few years
Once cleaned out you will probably find that the filling problem has gone away.

The water pump on the 2.5 is, as you say, behind the prop but it is on top of the gearcase, driven by the vertical drive shaft in the 3.3. No outboard with a neutral gear position can have the water pump behind the prop because it would not be operating when the gears are in neutral and the engine would overheat.

 

[QBhoy]

Hi. On some of these models, it’s fairly easy to get the top screw plugs mixed up. There are two on some of them. One is just at the top forward end of the torpedo gear housing and the other is above the cavitation plate. If you have the wrong one open…it will take an age to drain and obviously you won’t get to fill with oil properly. You’ll get a back pressure from the oil you’re putting in trying to displace air, that has nowhere to go. Id imagine this might be the case.

 

[dunedin]

If all is well the oil you drain should be "clear and bright" and no more than a little darker in colour than when new.
Black oil suggests to me that water has entered and caused corrosion of the bearings and gearbox internals. Hence my suggestion that it is dismantled cleaned and inspected and rebuilt with all new seals.
While it's off and stripped down it makes sense to fit a new impeller then you should not have to worry about it again for a few years
Once cleaned out you will probably find that the filling problem has gone away.

The water pump on the 2.5 is, as you say, behind the prop but it is on top of the gearcase, driven by the vertical drive shaft in the 3.3. No outboard with a neutral gear position can have the water pump behind the prop because it would not be operating when the gears are in neutral and the engine would overheat.

Do you have any link to some instructions (or video) of how to dismantle the gearbox on a 3.3hp?
Otherwise wouldn’t know where to start.
Thanks

 

[dunedin]

Hi. On some of these models, it’s fairly easy to get the top screw plugs mixed up. There are two on some of them. One is just at the top forward end of the torpedo gear housing and the other is above the cavitation plate. If you have the wrong one open…it will take an age to drain and obviously you won’t get to fill with oil properly. You’ll get a back pressure from the oil you’re putting in trying to displace air, that has nowhere to go. Id imagine this might be the case.

Don’t see two top plugs on mine - just one in a similar place to on the 2.5hp. Thanks

 

[QBhoy]

Don’t see two top plugs on mine - just one in a similar place to on the 2.5hp. Thanks

Is the one you removed above the gearbox and where it attaches ? Or below

 

[VicS]

Do you have any link to some instructions (or video) of how to dismantle the gearbox on a 3.3hp?
Otherwise wouldn’t know where to start.
Thanks

Service manual :- Mariner 3.3 Workshop Manual : Monty Mariner but it requires some special tools so may not be practicable to dismantle. Therefore flush with some light oil eg cheap engine oil

 

[VicS]

Is the one you removed above the gearbox and where it attaches ? Or below

The drain and vent plugs are identical so should be easy to identify.
Some outboards, but not this one AFAICS, have a (smaller) screw which retains the bearing.
Some older Johnson and Evinrudes have a screw near the drain plug which is a pivot pin for part of the gear shift. That often catches out the unwary.

 

[QBhoy]

The drain and vent plugs are identical so should be easy to identify.
Some outboards, but not this one AFAICS, have a (smaller) screw which retains the bearing.
Some older Johnson and Evinrudes have a screw near the drain plug which is a pivot pin for part of the gear shift. That often catches out the unwary.

Yeah. Just for a newbie to it…there are occasionally two upper plug screws. One is the right one…one isn’t

 

[John_P]

I had the same issue with a tohatsu 3.5hp (same engine). I bought it new and filled it from the bottom oil hole until it filled the gearbox and came out the top hole, it was perfect for many years, then one year when i changed the gear oil the top hole gearbox became blocked. I took the prop off then removed the front plate and filled from there, venting from the bottom oil hole with the engine tilted, it was a bit messy but worked as a temporary fix. For a permanent fix i stripped the gearbox down and found the top gearbox bearing and seal had dropped a few millimetres, just enough to block off the top filler hole. Rebuilt with new seals and bearings and waterpump housing (which broke when i stripped it down) and i can fill the gearbox properly as before.
I think that when I re insert the lower leg after an impeller change, knocking the top of the driveshaft as you try and reinsert it causes the seal and bearing to drop enough to cause your problem.