Brown Lower Unit Oil

BigJeff

Cadet
Joined
Apr 13, 2011
Messages
23
I beleive this means I have a leak in some seal for the lower unit. When I changed the gear lube last night there was a ribbon of brown in the old black oil.

Wondering how hard it is to work on the lower unit?

Is it usually a seal that goes bad or can it be worse and what to look for?

Also if it is just seals wondering how hard of a project this is and if I am taking it apart for this should I also be doing anything else, ie water pump, impeller?

I also noticed there are no washers or o rings on either the drain or vent plug, should there be?

96 Merc 135hp serial number OG362631



Parts Listing:

http://www.crowleymarine.com/mercury-outboard/1678.cfm

Service Manual:

http://1manual.com/Mercury manuals...52r3/cover.pdf
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: Brown Lower Unit Oil

How long since it was changed? The oil, depending on age, could darken some with time, so maybe not assume a big leak or problem. Leaks can be at those drain/fill plugs gaskets/washers which are supposed to be replaced at every oil change. The other potential leak points would be the prop shaft, drive shaft and shifter shaft. Maybe just refill it with fresh oil, replace those little washers, and then check it again after you run the motor for a few hours. The prop shaft seals, bearing carrier, etc. can be challenging to remove and require some special tools and expertise, so no need to jump on that project if it's not necessary. Remove prop and check prop shaft for fishing line wrapped around it, causing leak and/or seal damage. There is a pressure test for the lower unit to find a leak, if required. Good Luck!
 

BigJeff

Cadet
Joined
Apr 13, 2011
Messages
23
Re: Brown Lower Unit Oil

Robert,

I changed it last year at the begning of the season and it was fine, but I had just bought it then too. I will be picking up some fresh washers for those plugs and start there. IT wasn't a lot of brown and no clear liquid but always tring to stay out ahead of things. I will also check for the fishing line but I beleive I cleared that last year at the end of the season as well. I will run it this weekend for a bit and then see what things are looking like.

Will it turn the oil brown right away if any water is getting in?
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: Brown Lower Unit Oil

When you removed the drain plug was there much metallic particles on the magnetic tip? Just a bit of freshwater intrusion is no where near the problem as saltwater. If it gets brown/milky pretty quick, you may want to get a pressure test on it to see where it's leaking. Remove the lower unit and take it to an outboard dealer for the test, or you might be able to research it and do it yourself. The driveshaft seal and shifter shaft seal are fairly easy to access and replace, if they're leaking. Maybe/hopefully you don't really have a leak/problem. good Luck!:)
 

Mi duckdown

Commander
Joined
Apr 14, 2007
Messages
2,575
Re: Brown Lower Unit Oil

Jeff. make sure there isn't any part of those washers mashed on the drain and vent housing. I use a pick or tiny screwdriver to make sure.
 
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