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Author Topic:   Changing Lower Unit Gear Lube
kend posted 10-11-2003 10:07 AM ET (US)   Profile for kend   Send Email to kend  
I just changed the gearlube on my johnson 90hp What should the old lube look like ? It is a mustard yellow color,is this ok . I use the motor on a 17 montauk and usually run at high speeds.
Sal DiMercurio posted 10-11-2003 11:48 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Your fresh gear lube should be either amber or blue/green & it should come out pretty dark brown or blackish.
If it's milk shake colored or mustard, your seal is gone & theres water mixed with the oil.
cmarques posted 10-11-2003 06:53 PM ET (US)     Profile for cmarques  Send Email to cmarques     
I just changed mine a few weeks ago and it came out almost black but clean. Stunk in the garage a few days- will change it outside next time!
jimh posted 10-12-2003 07:07 PM ET (US)     Profile for jimh  Send Email to jimh     
The oil you drain from the lower unit should look like the fresh oil you are going to put in. If it is not the same color and viscosity, it has probably been contaminated with water. This is a sign of a bad seal.

There are two principal areas to be sealed. The propeller shaft is a prime location for a seal leak. The drive shaft also must be sealed where it enters the lower unit, usually just beneath the water pump.

Knockerjoe posted 10-13-2003 09:44 AM ET (US)     Profile for Knockerjoe  Send Email to Knockerjoe     
The exception to the rule is the new synthetic oils which tend to mix with the air and come out looking a little lighter colored than what was put in.
baybug posted 10-20-2003 10:01 AM ET (US)     Profile for baybug  Send Email to baybug     
I noticed that a couple of marinas are selling Mobil 1 Gear Oil (SAE75-90) for use in lower end units. I have a 90 hp Yahama 2s and use Mobil 1 in all my cars but wasn't sure if it should or could be used in lower end units. Any issues or is gear oil gear oil aside from being synthetic.
kglinz posted 10-20-2003 10:28 AM ET (US)     Profile for kglinz  Send Email to kglinz     
I changed to Pennzoil Synthetic because when I drained the oil, for oil change my counterrotating lower unit oil showed signs of being burnt. After running synthetic for a season, both lower unit oils drained out clean and as clear as when put in. Sal mentions oil coming out brown or black. Thats overheated oil. When engine oil turns black that is exhaust finding its way into the oil. I see no reason for lower unit to change colors unless it's been hot (brown or black) or has water ( milky ) or has metal particles ( silver ). Synthetic can run at much higher temps.
Sal DiMercurio posted 10-20-2003 09:08 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Baybug, only use what the manufacturer says to use.
In my case I use ultra hi visc by Bombardier.
The ultra hi is synthetic & is far superior then the non synth.
jimh posted 10-21-2003 08:01 AM ET (US)     Profile for jimh  Send Email to jimh     
Is there any reason not to use Synthentic oil in the lower unit of older outboards? Generally I see it recommended for high horsepower motors and out drives.
skookum point posted 10-28-2003 11:18 PM ET (US)     Profile for skookum point  Send Email to skookum point     
I drained my gearcase (OMC 50hp)and thought the lube looked ok coming out. But while I was away for a week I left the plug out to get complete drainage, and now, looking at the clear bottle containing the drained oil I see that it has seperated - the top 95 percent looks the right color but the bottom strata is milky. This was done indoors so there is no rainwater involved.

I assume a reseal job is in order and since it looks like lower unit disassembly requires special tools and expertise, I'm not inclined to tackle it myself. This motor is due for a waterpump impeller changeout anyway. So, my question is, how much should I expect to pay for this kind of job?

To make matters worse there seems to be a bit more play in the prop shaft than I would expect when wiggled side-to-side and up-down.

Otherwise the lower unit appears undamaged and performed normally last time out. Do I need a complete rebuild?
If the repair bill is around the thousand-dollar mark (or more), I'll want to replace the motor with a new one.

It would be great if someone could advise me with a ballpark guesstimate of the repair cost so I can make the replace-or-repair decision.


RMS posted 10-29-2003 09:32 AM ET (US)     Profile for RMS  Send Email to RMS     
Water contamination of the lower unit can also be caused by a damaged or missing washer on the fill and vent plugs. Bob
skookum point posted 10-29-2003 12:17 PM ET (US)     Profile for skookum point  Send Email to skookum point     
Very good point Bob. It might be a very simple fix. I think I'll improvise a means to lightly pressurize the unit to determine where the leak is.
Bigshot posted 10-29-2003 02:25 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Hold up their guys....don't start an oil panic. I have changed many lower units. To find a little milk is not a big deal, to find it all milky is. If you drain it and there are some swirls in the bucket, no biggie. It will also seperate overnight. If water comes out, then a reseal is in order. If I drain a lower and find some funky stuff, I refill and use it say 5-10 hours and do again. If it is clean that time, then she is OK.

My 70 4 stroke caught some mono and luckily I found it soon. When I drained it there was some milky oil at first and then clean. I refilled and did it again at about 10 hours and no water. Last time I drained it she had about 70 hours on it and the oil was pretty black. Normal for regular oil that is doing its job, just like engine oil. My oil might also get hotter being the gear ratio is much higher and water is 90+ degrees and on a jackplate. Make sure washers are good and let her rip. Remove prop and look for fish line, etc.

Synthetic is great but Mercruiser does not recommend it unless a total rebuild was done or used from the start, hence why I am a tad nervous to switch from regular oil in my outboard. My theory is synthetics in cars and 2 stroke resevoirs are compatible, why not lower units? Any thoughts?

Don't sweat anything except massive metal shavings or metal chunks coming out:)

jimh posted 11-02-2003 10:43 AM ET (US)     Profile for jimh  Send Email to jimh     
I changed the lower unit lubrication on my twin engines last month. When I drained the engines there was a noticeable difference in the color between the two oils. I saved the oils into two separate soda bottles for reference. I was certain that one unit had a leak because its oil was a lighter color and more "milky", like coffee with cream.

I set the two bottle on the shelf in the closet for a month. I did not label them because there was such a difference in color it was obvious which was which. The soda bottles were sealed with screw-on caps.

I just looked at then yesterday. I could not tell them apart! The color was the same and there was no apparent separation of any water. I don't think the water could have evaporated, as the bottle was tightly capped.

Also interesting to note was the volume of recovered oil. It was very nearly identical. I would suspect that a severely leaking lower unit might have a change in volume, no?

kend posted 11-06-2003 10:40 PM ET (US)     Profile for kend  Send Email to kend     
Adding to my original post. I have tacken my 90 Johnson in for service. The service tech did a pressure test and cannot find a bad seal.The o rings are new. He he going to retest with better testing equipment he has ordered. The lube in the lower unit was LubriMatic hi- pro 80-90wt . Has anyone else had the drained lube come out a med brown color.It was not milky, Could it be burnt lube and not water.
Bigshot posted 11-07-2003 11:18 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Don't mess with it anymore. If you pump up too much pressure, you can make a good gasket go bad. No milk means no water. I do not condone lubrimatic oils personally. I like OEM or at least penzoil. Normal oil turns brown when it breaks down or gets diry, it is doing its job, just like in your car. If it was burnt, means oil is junk or you are running it hard. Fill it with good oil and run it, worry about global warming instead:)
TampaTom posted 11-10-2003 10:33 PM ET (US)     Profile for TampaTom  Send Email to TampaTom     
Some related links from an oil fourm.;f=13;t=000061;f=13;t=000036;p=1#000014

Video showing water/oil seperation with several gear oil brands. Interesting that Quicksilver and Mercury brands performed differently.

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