1975 Johnson 6hp 6r75r gearcase.

[tomhath]

If the lower unit is properly sealed where would the oil come out if it got hot ?

Oil expands when it gets hot. Normally the air will be slightly compressed and the seals will hold, but if there's no air the oil will escape where it can.

I just asked the question because he said it leaked after it sat in the hot sun.

 

[flyingscott]

How would you overfill it?

 

[racerone]

Does the aluminum housing get bigger ( more volume ) when it gets hot ??

 

[Rad2101]

Thanks guys. I will attempt to pressure test it. As far as filling the unit. I always fill from the bottom hole when the motor is upright and pump the oil in till it comes out the top hole. It shouldn't be over filled and would have some air in it. There's bound to be a leak somewhere so the pressure test will confirm that. Just need to work out where its leaking. What sort of pressure are we talking and how long should it hold for?

cheers

 

[racerone]

I often test them at 5 PSI---Leave at pressure overnight.-----Check for pressure drop the next day.

 

[boobie]

I test them at 14 psi for 15 min and then at 6psi for 15 min.. Squirt soapy water on the gear case to check for bubbles.(air leak).

 

[tomhath]

How would you overfill it?

Motor laying on the bench when it's filled so the vent hole is the highest point. I've seen gear cases on farm equipment push oil out, but they get a lot hotter than an outboard's gear case that's in the water.

 

[racerone]

When they built these outboard motors the old time knowledge went into them.-----A reasonable mechanic can not overfill them.------Farm equipment may have an open vent and yes oil could be pushed out.

 

[oldboat1]

+1 on at least a pressure test. If you know there is a leak somewhere, you can locate fairly quickly -- five or six lbs of air, and some soap mix in a spray bottle. Drain and remove the l.u. Use a small pump -- should have a gauge. (I use a foot pump intended for inflating boat bumpers.) Use the needle for pumping up soccer balls, etc., and a piece of rubber gasket. Hold the needle and gasket in an open fill or vent hole, with the other one sealed up. Air will escape out of the leak almost immediately, and show up as bubbles when sprayed with the soap mix.