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Author Topic:   Lower Unit Oil Leak from 1983 Merc 90 HP

jfbazb posted 11-09-2014 05:03 PM ET (US)
I pulled the Jargo for the winter today and winterized it in my driveway. After sitting for about an hour I came back and was surprised to see what appears to be a puddle of milky lower unit oil. Puddle is about the diameter of a baseball. Anyone have advice on what has failed or failing? I haven't pulled the prop yet. I have a picture of it ... how do you add pictures to your post?

Buckda posted 11-09-2014 05:27 PM ET (US)
Is it milky lower unit oil or is it oily residue/carbon from the winterization process? You should be able to tell by simply pulling the plug on the lower unit and draining the gear case of oil. If it is milky, it will need to be replaced this fall before a freeze anyway.
jimh posted 11-10-2014 09:23 AM ET (US)
You lost me at "Jargo."
dg22 posted 11-10-2014 12:20 PM ET (US)
Check to see that you have a nylon washer installed with the drain screw/plug on the lower unit.
acseatsri posted 11-10-2014 12:30 PM ET (US)
One of the winterization things on the list has always been changing the lower unit oil. This way if there was any water intrusion, you don't risk splitting the gearcase in freezing weather because there was water in the oil.
jfbazb posted 11-10-2014 09:50 PM ET (US)
Sorry Jimh ... Jargo is the name of my 1983 Montauk 17 with the original 1983 Mercury 90 HP 2-stroke. The lower unit was replaced by the previous owner about 5 years ago according to the local mechanic.
I wasn't planning on changing the lower unit oil till spring but given the milky oil situation I'm going to drain and refill it soonest chance. I put the muffs on it and gave it a good dose of fogging oil so hopefully that's what I'm seeing on the driveway. I'll report back later ...
jfbazb posted 11-18-2014 08:15 PM ET (US)
I drained the lower unit today after work (in 15 degree temps) and it looked good as far as water goes. There was no milky appearance at all to the oil. I think what I was seeing was lower unit oil leaking past the shaft seal and combining with cooling water coming out of the through hub exhaust. Does that make sense to anyone? Doesn't some of the cooling water coming through the hub?
I think this because I noticed a similar issue while the boat is in the water. If I am running the engine out in the lake and I stop the engine momentarily then restart it I notice small globules of milky oil floating around the engine area.
sosmerc posted 11-23-2014 01:04 PM ET (US)
It is not uncommon for an engine of that age to have worn lower crankshaft seals. This allows gas/oil to escape into the driveshaft housing and this creates a chocolate milkshake type gue that you see on the ground after running the engine on a hose. Also, the additives in our gas also tend to wash the carbon out of the exhaust and this will also leave a dark deposit on the ground that some people think is a lower unit oil leak. This "runout" stuff can vary quite alot depending upon the particular gas you are running.

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Author	Topic: Lower Unit Oil Leak from 1983 Merc 90 HP
jfbazb	posted 11-09-2014 05:03 PM ET (US) I pulled the Jargo for the winter today and winterized it in my driveway. After sitting for about an hour I came back and was surprised to see what appears to be a puddle of milky lower unit oil. Puddle is about the diameter of a baseball. Anyone have advice on what has failed or failing? I haven't pulled the prop yet. I have a picture of it ... how do you add pictures to your post?
Buckda	posted 11-09-2014 05:27 PM ET (US) Is it milky lower unit oil or is it oily residue/carbon from the winterization process? You should be able to tell by simply pulling the plug on the lower unit and draining the gear case of oil. If it is milky, it will need to be replaced this fall before a freeze anyway.
jimh	posted 11-10-2014 09:23 AM ET (US) You lost me at "Jargo."
dg22	posted 11-10-2014 12:20 PM ET (US) Check to see that you have a nylon washer installed with the drain screw/plug on the lower unit.
acseatsri	posted 11-10-2014 12:30 PM ET (US) One of the winterization things on the list has always been changing the lower unit oil. This way if there was any water intrusion, you don't risk splitting the gearcase in freezing weather because there was water in the oil.
jfbazb	posted 11-10-2014 09:50 PM ET (US) Sorry Jimh ... Jargo is the name of my 1983 Montauk 17 with the original 1983 Mercury 90 HP 2-stroke. The lower unit was replaced by the previous owner about 5 years ago according to the local mechanic. I wasn't planning on changing the lower unit oil till spring but given the milky oil situation I'm going to drain and refill it soonest chance. I put the muffs on it and gave it a good dose of fogging oil so hopefully that's what I'm seeing on the driveway. I'll report back later ...
jfbazb	posted 11-18-2014 08:15 PM ET (US) I drained the lower unit today after work (in 15 degree temps) and it looked good as far as water goes. There was no milky appearance at all to the oil. I think what I was seeing was lower unit oil leaking past the shaft seal and combining with cooling water coming out of the through hub exhaust. Does that make sense to anyone? Doesn't some of the cooling water coming through the hub? I think this because I noticed a similar issue while the boat is in the water. If I am running the engine out in the lake and I stop the engine momentarily then restart it I notice small globules of milky oil floating around the engine area.
sosmerc	posted 11-23-2014 01:04 PM ET (US) It is not uncommon for an engine of that age to have worn lower crankshaft seals. This allows gas/oil to escape into the driveshaft housing and this creates a chocolate milkshake type gue that you see on the ground after running the engine on a hose. Also, the additives in our gas also tend to wash the carbon out of the exhaust and this will also leave a dark deposit on the ground that some people think is a lower unit oil leak. This "runout" stuff can vary quite alot depending upon the particular gas you are running.