2000 90 YAMAHA Lower unit gear lube black and burned smelling

markernineteen

Seaman Apprentice
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Feb 21, 2007
Messages
48
The gear lube in my lower unit is black and burned smelling . I change it twice a year and I'm using the best synthetic gear lube . There is no water or metal flakes in the drained oil . Is this normal for this lower unit ? I've never seen an outboard do this to gear lube . Everything works fine and the prop spins freely and smoothly by hand . This smell has me worried and it has happened with three brands of oil . Is trouble on the way ?
 
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robert graham

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Apr 16, 2009
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Re: 2000 90 YAMAHA Lower unit gear lube black and burned smelling

if everything is as it should be, then the gear oil drained from your lower unit should look just about like new oil. sounds like you may have a bad seal/water in unit. remove your prop and check the seal. could also be drive shaft seal on top of foot which would require foot removal to inspect. if you run motor in salt water, then oil/water mixture in foot can get pretty nasty. Good Luck!
 

hondon

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Jun 11, 2001
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Re: 2000 90 YAMAHA Lower unit gear lube black and burned smelling

We're not there to see what you are seeing but it do'es not sound right.Centered around the driveshaft in the gearcase is a nylon wormgear that circulates oil from the bottom of the gearcase to the top and allows it to cool.If that gear has become spun on the flats of that shaft it will cause the gearoil to overheat and spoil very quickly.Not a common failure but not unheard of especially if that gearcase has been gone through and that nylon gear not replaced.
 

JustJason

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Aug 27, 2007
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Re: 2000 90 YAMAHA Lower unit gear lube black and burned smelling

use the mercruiser high performance (green stuff) in it and see if your problems return.
 

matarco

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Sep 17, 2010
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Re: 2000 90 YAMAHA Lower unit gear lube black and burned smelling

Markernineteen, did you find out what the issue was? I have a 1989 90 hp Yamaha 2 stroke with the same symptoms (dark, smelly gear oil) and would like to know whether it is likely resolved by changing the oil, or do I have a bigger issue lurking.
 

markernineteen

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Feb 21, 2007
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Re: 2000 90 YAMAHA Lower unit gear lube black and burned smelling

WOW ! What a coincidence , I started this thread three years ago , I click on iboats forum today and there it is . To answer your question I have not had any trouble with my lower unit . I still change the lube twice a year using the best synthetic lubes ( tried five different brands and they all end up burnt looking and smelling ) I don't really know how many hours I run the boat a year but it's a LOT! This is a great outboard it will run wide open or troll all day if you feed it clean fuel . Maybe RODBOLT can solve this puzzle for us . MARKERNINETEEN
 

matarco

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Sep 17, 2010
Messages
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Re: 2000 90 YAMAHA Lower unit gear lube black and burned smelling

Wow, that was fast. Thanks for the reply. I love the motor as well. This last weekend the temp alarm went off at high speed (first time that has happened). I am doing the normal thermostat and water pump change. When I popped off the water pump - Whew, that gear oil really smelled. I am hoping it is nothing major. It has been about a hear since it has been changed, but not that many hours on the water. No other symptoms, but I hope it just needs new oil.
 
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