Lower Unit Oil?

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I have a 1998 Mariner 40HP. Over the last 5 years of ownership I have been using Yamalube Gear Oil like the one pictures on the left. Today I went to the same boat dealer I always go to that told me the Yamalube oil is what I need. And told them I need lower unit oil. Told them what I had and they told me the Mercury Oil thats pictured on the right. I was hasitent to buy it cause I know I always used the Yamalube, I just wasn't 100% sure what weight. So I bought the Mercury Oil. I get home and go to put the oil away until Monday when I plan to change it and saw that I already had a bottle of the Yamalube. And then I noticed the weights. The Yamalube is SAE 90, 80/90 the Mercury Oil is SAE 90. The brand I could care less about because I'm sure the quality is the same. I'm just confused about the weights.

According to the manual I downloaded off the internet it says to use Quicksilver Gear Lube Premium Blend which is a 80W90.

So which one of the 2 pictured do I use?

EAE6A68F-ABDC-44E4-A83A-52B54E757EAF.jpg


Wayne
 
It won't matter either way. If you want something better use synthetc LU gear lube. I have a 60Hp 1993 Merc that is in pieces. I will be using Amsoil.

Have fun......
 
Yes the Yamalube I bought last year, the Merc I bought yesterday.

Curious how a oil can be both 80W90 & SAE 90. I'll admit I know little about oil, but didn't think that a oil could be two different weights.

Since the Yamalube is labeled 80W90 & SAE 90 and the Mercury is only labeled SAE 90 should I even use it, because the manual says to use 80W90.

Sorry if these questions are retarded. I have a huge OCD issue with over thinking things. I have always been pretty anal about what parts and products I put on my boats and trucks but lately I have been over thinking so much it's giving me a headache due to the information overload I get from researching the smallest things.

Can't just except the fact that both will work. Need to forgive out why one is labeled 2 weights and 1 labeled only one.

Wayne
 
I imagine the 80w90 is also labeled SAE 90 for the people that see SAE 90 in their owners manuals and won't use anything else. I'm not certain. That's just my thought.

In any case, the lower unit is nothing complicated. Use either.
 
Main this is change it before it's worn out. Also make sure no water contamination, or fishing line around the prop shaft. The other stuff you are worrying about is a non issue.
 
seems to me the 90 wt is straight 90 wt and the 80/90 is a 80 wt base stock with some viscosity modifiers to reach 90 wt at warm temperatures. You have absolutely nothing to worry about here. I started driving in the 1970's and I have never changed the gear lube in a differential of a car. They just never go bad. The lower unit of a outboard is one of the last items to go and only if the seals develop a leak. Don't over think things that do not matter. For the most part you car engine as well as boat engine will outlast the fiberglas and upholstery it is mounted to by a long shot.
 
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