Lower unit drain plug

[charles90yam]

I am attempting to change the gear oil in my 90hp for the first time. The drain screw (plug) won't seem to budge. I am using a large slotted screwdriver, even a wrench on the screwdriver shaft. The top plug comes out OK. Since I haven't done this before I didn't want to force it if I should be doing something different. Also, there is what appears to be a round indentation across the slot. I am wondering if that is for a special tool. My service manual doesn't mention anything about this.

Thanks for the help!

[rodbolt17]

run down to the local auto parts place and buy the special tool.
its called a hand impact driver.
works wonderfully.

[boscoe99]

No special tool is needed although an impact driver is nice.

Very important to have a screwdriver blade that completely fills the slot in both width and thickness.

Just put more torque on the screwdriver if you don't want to get an impact driver, and it will come loose. I like to use a square shank screwdriver with a Mexican speed wrench doing the turning as I press in on the handle of the screwdriver.

People are scared of a screw/bolt coming loose and usually apply twice the tightening torque that is needed. So, don't over tighten when you reinstall the screw.

[99yam40]

and do not forget the new gaskets for the drain and the vent when putting back in

[boscoe99]

and do not forget the new gaskets for the drain and the vent when putting back in

Good point. And make sure the old gasket is not stuck inside the gear case in which case you might have two gaskets installed. Not good.

And don't be in a hurry to complete the job. Fill until air free oil comes from the vent hole. Take a five minute break. Add more oil if needed. Install the vent plug and then, as quickly as possible to minimize loss, install the fill/drain plug.

Some gear cases have lots of nooks and crannies and it can take some time for thick oil to find its way into those hidey holes.

[robert graham]

I took my big gorilla screwdriver and filed the blade until it is a perfect fit into the slot of the drain plug....

[charles90yam]

drain plug - Thanks !!!

Thanks so much rodbolt17, boscoe99, and robert graham! This is great information and so helpful. It is great to hear from so many knowledgeable folks.

[robert graham]

There is an after-market drain plug that has an Allen head instead of the slot....always seemed like a nice idea to me, but since I've had no problems with the slot-head item, never went that direction...yet...