Do all lower units need to be oiled separately than the oil you mix with the gas?

If so, how often for an 1979 85HP Evinrude?

Yes , fill them with lower unit oil ( 90 weight marine grade ) which is different from two cycle oil mixed with the gas. . It is recommended to change every 100 hours or every fall before the first freeze. Two screw in plugs top and bottom of the L.U. are used to drain and fill with the oil.

I use this in mine:

^Ditto what he said. Change every Fall and use QS HP Gear Lube. Remember to pump the new oil into the drainhole.

Thanks Keith. I will get this taken care of this weekend!

Your welcome.
What Toxarch is talking about is in the following instructions given to me:

Remove lower vent plug
Remove upper "vent" plug.
Once COMPLETELY drained, fill from lower plug opening with suitable "pump". Continue filling until fluid level JUST REACHES the upper "vent" opening (DO NOT OVERFILL til it's spewing out). Allow excess to spill out of vent.

Reinstall upper vent screw and sealing washer.

Remove pump from lower "fill" opening... allow approximately 1-2 ounces to spill out (take your time getting the screw and sealing washer into place).

Tighten drain/fill screw securely.

The reason to let an ounce drain is the L.U. becomes pressurized when running and heated. This amount let out is to allow for expansion of the oil In a worst case scenario the pressure of an over filled L.U. could allow an intrusion of water and some cases pop seals in the unit.

Good Luck

I would recommend replacing the washers. They are cheap compared to ruining a lower unit due to water infiltration.

Since the boat was given to me, I do not have the manual for the motor. Any ideas where i can find detail instruction on how to change the lower unit oil or a site with PDF manuals?

just purchase the items that Keith listed from Walmart. get a new set of washers(they are pretty much universal i think). follow Keith's instructions. bam! you are done.

OOPS! I for got to mention the new washers

Thanks H2O Dawg

Here is a video on youtube that pretty much explains how to do it. The only thing he DOES NOT do is let one ounce drain after he fills it up. Good Luck

http://www.youtube.com/watch?v=gkU-xdNW-3M

PlanoKeith,
I have never heard of letting an ounce drain after filling it. What you say makes sense but have you ever heard of this causing problems if not drained? I've always filled mine until it starts coming out the top hole. Yes, I've lost a little when removing the pump from the bottom but usually do it quick to try & not lose very much. Thought it was supposed to be full!

John That is what my Mercury tech told me to do and he has over 30 years experience so I just do what he tells me. Plus The previous owner of my boat hit something and bent the prop shaft and and who knows what else. After I took it out for the first time I noticed some seepage from where the L.U meets the powerhead and thats when he told me that the lower unit builds up pressure when running for long periods of time due to the heating and expansion of the gear oil. It made perfect sense as to why the oil was coming out of the top of the L.U. because I had a shift shaft seal loose. He also found water in my L.U and said that a previous freeze probably pushed the seals out on top of the unit so I had him fix it.

I have never heard of any problems before regarding not letting an oz out. I think he does this to make sure that there is no possibility of over filling. I have heard of seals being damaged from over filling a L.U. because unlike an automobile gear case a L.U. has no vent for oil expansion. Hope this helps

I've never let that much oil run out when removing the pump. Some, but not much. I guess I can let more out next time.

Okay guys , I found out why you should let it drain an ounce after filling AND!!! on which gear case. ONLY on the TorqueMaster Gear case with the sharp nosecone because this gear case runs higher out of the water and gets a lot hotter than the regular L.U. So I was some what wrong about it. This only applies to High performance lower units.

So I stand corected Sorry Guys