90 hp Mercury lower unit oil

Mrnecks

Cadet
Joined
Jul 16, 2013
Messages
8
What type and how much oil goes in the lower unit of a 90 hp mercury outboard?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: 90 hp Mercury lower unit oil

An Inline six motor will take 25oz. A big foot motor (if there is one in that HP) would take a bit more. In either case you need to buy a quart.
 

wired247

Lieutenant Commander
Joined
Oct 8, 2011
Messages
1,557
Re: 90 hp Mercury lower unit oil

Just buy a quart and fill from the bottom hole until it comes out the top hole. The quart will be more than enough.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: 90 hp Mercury lower unit oil

I have that engine. Go to WW and as Chris and wired said buy a quart of Quicksilver/Mercury Premium LU oil in the quart in the package that has the pump. Makes it a nice clean simple job. On the 6 cyl engines remove the vent plug at the top and drain on the bottom. On the 3 cyl engine like mine, there are 2 vent plugs on top. Ensure that you have the washers (mine are blue) under the screws to seal the screws.

Screw the pump adapter into the drain plug and with the one vent engine pump till you have oil coming out and then a little more to reduce the bubbles. Don't have to get them all out. On the 2 vent plugs do the same as before but when the oil starts coming out of the front vent, plug it and continue pumping until it also comes out of the aft plug and cap it.

Then with a cleaned off magnet on the drain screw....mine has it, some don't, remove the pump adapter and insert the screw. Loosing some oil is normal but keep it to a min. Use a big screwdriver to keep from dinging up the screw slots and get them tight using both hands.

Engine should be vertical in the fill/drain processes.

Mark
 

Mrnecks

Cadet
Joined
Jul 16, 2013
Messages
8
Re: 90 hp Mercury lower unit oil

Thank you for the info, really am enjoying this site and all the help it has to offer!
 

jasonbailey

Petty Officer 1st Class
Joined
Jul 25, 2004
Messages
253
Re: 90 hp Mercury lower unit oil

I have that engine. Go to WW and as Chris and wired said buy a quart of Quicksilver/Mercury Premium LU oil in the quart in the package that has the pump. Makes it a nice clean simple job. On the 6 cyl engines remove the vent plug at the top and drain on the bottom. On the 3 cyl engine like mine, there are 2 vent plugs on top. Ensure that you have the washers (mine are blue) under the screws to seal the screws.

Screw the pump adapter into the drain plug and with the one vent engine pump till you have oil coming out and then a little more to reduce the bubbles. Don't have to get them all out. On the 2 vent plugs do the same as before but when the oil starts coming out of the front vent, plug it and continue pumping until it also comes out of the aft plug and cap it.

Then with a cleaned off magnet on the drain screw....mine has it, some don't, remove the pump adapter and insert the screw. Loosing some oil is normal but keep it to a min. Use a big screwdriver to keep from dinging up the screw slots and get them tight using both hands.

Engine should be vertical in the fill/drain processes.

Mark

Excellent instructions. The only thing that I do additional is, replace the gaskets around the drain and vent plugs. Mine are yellow. West Marine has them as well as your local Merc dealer. They are not cheap at the dealer, I think they gouged me for $9.00 for the three of them. Replacement is up to you, but I figure might as well be safe and replace them.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: 90 hp Mercury lower unit oil

Excellent instructions. The only thing that I do additional is, replace the gaskets around the drain and vent plugs. Mine are yellow. West Marine has them as well as your local Merc dealer. They are not cheap at the dealer, I think they gouged me for $9.00 for the three of them. Replacement is up to you, but I figure might as well be safe and replace them.

Totally agree but if the guy has no access and his oil was good he is probably good to go. I use the blue ones that I get from the local marine dealer, but have heard about the high dollar new and improved, reusable yellow ones. With you on this man.

Mark
 
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