What Color Should Lower Unit Gear Oil Be?

Working in the marine industry and changing gear case oil for years, you get to see a lot of weird stuff. A lot of different colors and failures. From holes in the gear case to half of the gear case missing!

Changing the gear lube on your lower unit is a must! There are no warnings for lower unit failure. So knowing the color of the gear lube and what it means is extremely important!

What Color Should Lower Unit Gear Oil Be? Brand new gear oil should be a shade of blue, green, brown, or yellow, depending on the brand. Used gear oil should be a black/dark variation of the brand new color.

Knowing what these colors mean and also the other colors you will encounter is important. Here are a few variations, colors, and failures that you might encounter and what they mean.

What Brand New Lower Unit Oil Looks Like

Brand New lower unit oil

Knowing what color the gear lube was in the beginning will give you a base to start from. There are different variations in color depending on what manufacturer gear oil you are using and what you are putting the gear lube in.

Lower unit gear oil

Mercury’s High-Performance Gear Lube is a blueish or greenish color. Mercury uses the same gear lube in almost all of their lower units.

They do also make a Racing Gear Lube for their Racing models. That gear oil is more of a yellow or brownish color.

Then on some of their little engines, such as most of their kicker models, 2.5, 5, 9.9 HP engines. They will have a clearer colored oil in them.

Lower unit gear lube

Yamaha has two different types that are used regularly. They have their regular gear oil. Then they have their HD Yamalube.

Here in the glass jar is the regular gear oil. This is used in almost all of the Yamaha outboards with only a couple of exceptions that we will talk about next.

Both the HD and Regular Gear Oil are a Yellow or Brownish color.

Yamaha outboard lower unit oil

A rule of thumb for the models that require the HD Gear Oil is the oil filter.

If the engine uses an N26-13440-02-00 oil filter, or an N26 for short. Then that engine requires the HD Gear Oil, which is to the left and is also a brownish or yellowish color.

It is extremely important that you get the right gear oil into the lower unit that you have. There can be premature failures caused by improper lubrication if the wrong gear oil is used!

What Color Should the Used Gear Oil Be?Used outboard gear oil

Black is good! If the gear lube comes out looking really dark, black or burned, don’t be alarmed. If it smells burnt and stinky, that is actually not a bad thing.

That is what you want to see. It is a good sign that there isn’t a leak anywhere in the gear case gaskets or seals, allowing water to get into the lower unit and contaminating the gear oil.

You also want to be looking for a darker shade of the original color. If you are working on a Yamaha, you should expect to see a darker yellow or brownish color. You want to see that darker shade.

Watery outboard gear lube

If you are working on a Mercury, you are looking for a darker blue or greenish color. Seeing these colors will let you know that the seals are not leaking.

It is a good idea to still do a pressure test on the gear case to double-check them. Basically, you can then service the gear case as normal, just changing the drain screw seals.

Something else to think about is how much time is on the gear case. If you are changing the gear lube on a brand new engine.

Then you are just after the break-in period and the gear lube might look brand new but have some metal in it.

If you want to know more about How To Break In A Brand New Engine, you might find a lot of great information in that article that we have published there!

Seeing a small trace of water isn’t the end of the world either. This just lets you know that you need to perform that pressure test and change a seal somewhere.

Here are two videos we created that may assist you on servicing a Yamaha or a Mercury Verado Gear Case:

What Colors Do You Not Want to See?Very bad gear lube

Broken lower unit parts

Clear, Gray, or Milky White! Don’t worry, it’s not the end of the world, yet! But these are the three colors that you are not excited to see. Sorry, but it’s true. Here’s what they mean …

Grey is definitely a bad sign. If you have grey gear oil, that means metal, a serious amount of metal!

Grey means that a gear, bearing, or another component has failed inside of the gear case and then was ground to powder, and mixed into the gear lube.

Grey is usually a sign that the gear case is blown up. A lot of times when the gear lube comes out grey, the expense of a rebuild outweighs the expense of a new one.

There is no telling what kind of damage and warping has been done to the other components inside of the gear case when a gear or other component inside a gear case fails and is ground into pieces.

This is a time when one needs to seek professional advice and expertise!

Outboard lower unit full of water

Then we have the clear gear lube! Or, well, that is … Straight water! This is a sign to be concerned about.

But at the same time, I have personally seen and rebuilt water-filled gear cases that actually worked afterward! (Now, I’m not saying that this is common. Because water is a likely sign that there has been damage done to the inners of the lower unit.)

The brand of the lower unit also bears some discussion. There are some gear cases that hold up a little better than others under these conditions.

I will have to say that from experience and opinion. I find that the Mercury Verado 5.44 Lower Unit stands up the best out of all of the other lower units in the common marketplace.

(Here’s a really interesting article we wrote that’s all about Mercury Verado Problems!)

Milky lower unit oil

Obviously, there are heavy-duty gear cases like the ones on Seven Marine engines. Those are just not as common in the recreational boating world!

Milky White is probably the best one of the worst colors you don’t want to see. Milky White usually means that you have caught the issue just in the nick of time!

When you see the milky color, that means that there was enough gear oil left to mix with the water and still properly lubricate the moving gears inside the case.

Most of the time you can just pressure test the lower unit. Replace the leaking seals, and put the lower unit back in service with no harm done! (Most of the time)

What Does Brown Oil Mean?

Brown lower unit oil is a sign of rust and is usually found in a gear case that has been sitting for a while. For example, in a boat that is put in storage and left for a season, or a year or two.

If there was any water in the lower unit when it went into storage, then the water and gear oil eventually separated.

Allowing water to get into the lower parts of the gear case, shifting mechanisms, bottom portions of the gears (when they were still), and the bottoms of the bearings.

All of the rust is ground off of the bearings, and gears, once the boat is taken out of storage and ran for a little while. This creates a brownish color, due to the rust mixing with the water and gear lube.

Should You Service Your Own Gear Case?

Absolutely! If you are a do-it-yourselfer, or just cautious, then changing the gear lube in your lower unit is a great thing. Don’t let the thought of it intimidate you.

There is always YouTube! Remember, there are no warnings when it comes to gear cases. When a gear case goes, it just goes.

If you put a lot of time on your engine without checking, or go years without service, this can cause warping of the rubber seals in the lower unit, due to heat and season changes.

There are also a lot of other things that can happen like if you bend a propeller blade and don’t necessarily know it! You might even want to read this interesting article we wrote about Whether A Bent Propeller Can Be Repaired or When To Replace it!

It can also dry the seals out, causing them to crack, or a spring to fail. If you don’t have the oil changed or service the gear case, you won’t know until it’s just too late!

Changing the gear lube is a fairly simple process and doesn’t take an expert and now you know what the colors are and what they mean. Plus, you will know when to call in the experts.

Here’s some more really helpful information about Checking The Spark & Compression of Your Engine that you can easily follow to check on the health of your engine!

Check Us Out!

We hope that this has been insightful and allowed you to understand a little bit more about lower unit gear oil and what to look out for when checking it!

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Here are some other super helpful articles that you might find interesting!

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Take care and be safe out on the water!

Aaron Hilligoss

Aaron has been working in the Marine Industry for over a decade and holds certifications for Yamaha and Mercury Marine. It is not uncommon for him to own and be working on at least three different boats at any given point in time!

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