Replacing lower unit gear oil on '90- 90 HP Nissan

[soak 'n fused]

Hi all- What is the reason for having to fill gear oil from the bottom hole so important. I buy the small tubes of gear oil and when I have to switch to a new bottle I lose a bunch of oil and then when it is full I lose more trying to get the screw back in. I just topped it off through the top hole and went with it. Is there a better way aside from buying a bigger bottle or a pump kit? Will it hurt it to fill from the top hole?

 

[TGuy]

Re: Replacing lower unit gear oil on '90- 90 HP Nissan

You fill from the bottom hole because the air that is in the lower unit has to go somewhere. If you fill from the top hole, you may not really end up filling it up as much as you think because of the air pocket that you're creating.

 

[soak 'n fused]

Re: Replacing lower unit gear oil on '90- 90 HP Nissan

You fill from the bottom hole because the air that is in the lower unit has to go somewhere. If you fill from the top hole, you may not really end up filling it up as much as you think because of the air pocket that you're creating.

 

[polychromeuganda]

Re: Replacing lower unit gear oil on '90- 90 HP Nissan

A short term solution is to leave the screw in the upper hole until you have the tube in the lower hole, then open the upper hole. Close the upper hole before removing the tube from the lower hole. If the screws are a hassle, use a little flap of duct tape, but degrade the adhesive with some dust or lint so it won't yank the paint off.

The long term solution is to invest $5 in a gear oil pump and adapter and pump it from the quart bottles. The gear oil in the little tubes isn't better, nor is it better than the 80W gear oil at the auto parts store and the difference in price will pay for the pump the first time you use it.

 

[soak 'n fused]

Re: Replacing lower unit gear oil on '90- 90 HP Nissan

thanks polychro and tguy for the advice i kind of knew about the air thing but i, i hope like a few of us others, just need a bit more confidence doing maintenance on their own boats. you know what a marine mechanic charges nowadays? i think its like at least $80 again thanks guys