Does this indicate water in lower unit oil?

davidmbv

Petty Officer 2nd Class
Joined
Apr 19, 2021
Messages
115
I changed the oil in the lower unit of my 71 25hp Johnson and noticed the oil looked tannish yellow while draining. See image of what I’m talking about. The other two outboards I also changed looked normal / dark-black colored. This is the first time I changed the lower unit oil on this particular outboard but I know it was done two years ago by a shop. I didn’t see any water drain out and I believe after the initial drain the oil then looked blacker. If this could mean a seal issue, what’s the best way to pressure test? Do they make an attachment? Or do I retro fit some kind of gauge to thread it the fill/drain hole ?
Thanks
 

davidmbv

Petty Officer 2nd Class
Joined
Apr 19, 2021
Messages
115
I changed the oil in the lower unit of my 71 25hp Johnson and noticed the oil looked tannish yellow while draining. See image of what I’m talking about. The other two outboards I also changed looked normal / dark-black colored. This is the first time I changed the lower unit oil on this particular outboard but I know it was done two years ago by a shop. I didn’t see any water drain out and I believe after the initial drain the oil then looked blacker. If this could mean a seal issue, what’s the best way to pressure test? Do they make an attachment? Or do I retro fit some kind of gauge to thread it the fill/drain hole ?
Thanks
 

Attachments

  • BAA8D1DB-0C99-4A89-A7D0-8C3A38EEE670.jpeg
    BAA8D1DB-0C99-4A89-A7D0-8C3A38EEE670.jpeg
    1.3 MB · Views: 12

saltchuckmatt

Lieutenant Commander
Joined
Jul 19, 2019
Messages
1,681
Some oils look that way. If it's been sitting then water should come out first. Vacuum or pressure test to 15 lbs or so.....you can make a tool.

You might be ok.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,590
If standard Auto 80/90w was installed it will turn "baby poop yellow" due to foaming.
 

davidmbv

Petty Officer 2nd Class
Joined
Apr 19, 2021
Messages
115
Great info thanks. I replaced the oil with west marine high viscosity 80W-90 lower unit gear oil.
I changed the lower into oil in a 72 Johnson I’m fixing up and now it’s leaking from the drain plug screw. It’s was very low on oil. I placed a new OMC white washer on it but still has small leak. Anyone ever have to use thread tape or another sealant on the drain screws ? I noticed the previous owner used plumbers tape and had a o-ring type washer on the problem screw…
 

saltchuckmatt

Lieutenant Commander
Joined
Jul 19, 2019
Messages
1,681
Behind the screw on the case, make sure it's not corroded up. Clean it up so the washer seats nice. No tape should be needed.
 

Vic.S

Rear Admiral
Joined
May 4, 2004
Messages
4,690
Great info thanks. I replaced the oil with west marine high viscosity 80W-90 lower unit gear oil.
I changed the lower into oil in a 72 Johnson I’m fixing up and now it’s leaking from the drain plug screw. It’s was very low on oil. I placed a new OMC white washer on it but still has small leak. Anyone ever have to use thread tape or another sealant on the drain screws ? I noticed the previous owner used plumbers tape and had a o-ring type washer on the problem screw…
Be sure there is not still an old, damaged sealing washer in the hole.

Most drain plugs use the flat plastic washers but a few use an O ring.
Look at the underside of the screw head. If it is flat it should have a flat washer.
If it has a recess it should use an O ring.
If you fit a flat washer to a screw which should have an O ring, or vice versa, it will sit raised rather than flush with the outside of the gear case.

When you drain the old oil from the gearcase it should be 'clear and bright' in appearance but perhaps a little darker in color than when new.
If the oil is milky looking it indicates that water has entered.
 
Last edited:

Crosbyman

Rear Admiral
Joined
Nov 5, 2006
Messages
4,915
if fixing a leaky GC is not your piece of cake and shop repairs are to much $$$$... oil is cheap and some just replace it mid season.
 

airshot

Rear Admiral
Joined
Jul 22, 2008
Messages
4,222
I use full synthetic 75/140 gear lube which is very light in color. Most dino lubes are darker in color. Flush it, put in new then watch it !!
 

Diplomasta

Cadet
Joined
Feb 27, 2021
Messages
24
Use marine rated gear oil. All automotive gear oil is GL-5 which is high detergent. Can damage soft metals. Also they don't have the corrosion and moisture resistant additives that marine grade does. I've seen that yellow oil before. It's certainly not what you expect to see coming out of there.
 

davidmbv

Petty Officer 2nd Class
Joined
Apr 19, 2021
Messages
115
Hopefully the strange color is from the shop who had originally serviced it used cheap oil. I’ll run it a few times and check for water intrusion. If I find water, I’ll pressure test it and replace the necessary gaskets/seals. I found some good YouTube videos on the procedure. Luckily I’m fortunately enough to have two backup motors and may as well learn all there is about servicing these cool old motors.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,051
The 71 model 25 HP is the ultimate in light weight performance.------Easy to maintain and consumable parts are everywhere at reasonable prices.----EG---Ignition coils were $30 about 50 years ago and still about that price today.
 
Top