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75 model 85 hp Johnson Lower Unit Leak

M

Marshall Smith

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"I changed the lubricant in th

"I changed the lubricant in the foot gear box using automotive type 90 wt oil. Now it leaks a little. I have since learned that automotive grease causes pressure. If I replace the oil with the proper marine oil, will that fix it? Or will the seal have to be replaced?"
 
"Marshall, you could give it a

"Marshall, you could give it a try and cross your fingers. But if you ran it with the auto oil in there, there is a good chance you have blown one of the seals..."
 
"Are you sure it is the oil le

"Are you sure it is the oil leaking, or is it just unburned fuel/oil running out of the exhaust?

Oil does not cause pressure, heat does. Automotive gear oil will not create any more pressure than gearcase oil. The main difference in the oils, besides the viscosity, is that the gearcase oil mixes better and stays mixed longer with water. This gives you more protection in the event you get water into your gearcase.

I would recommend having your gearcase pressure tested and then filling it with OMC Hi-Vis gearcase oil."
 
"Rick, I agree under normal co

"Rick, I agree under normal conditions that automotive gear oil will not create more pressure. However, I have long understood that automotive gear oil, with a lower GL rating will foam and expand if mixed with water - which could well occur in the lower unit of an outboard.

I have undone filler/vent plugs in lower units and had them practically blown across the shop from the pressure, followed by a goopy gray foam spewing out. The pressure I have seen could well blow out a seal that was on it's way out in the first place.

At least in the northern regions where I am we have seen that it is near impossible not to get some water intrusion in a lower end because of the drastic temperature fluctions.

So, while I do agree that an automotive gear oil with an API GL-5 rating should work fine in an outboard, have always just found it easier to say "no", don't use automotive oil, make sure it's marine rated."
 
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