Can You Fill Lower Unit Oil from Top? (Guide)

can you fill lower unit oil from top
can you fill lower unit oil from top

We’ve all planned out how we’ll be upgrading our fishing system to make it more robust. While anglers usually don’t have the budget or the knowledge to get the most premium option from the get go, they do fantasize about owning the top tier unit.

Even if you’re sitting on cash and have money to get the most premium unit, the missing knowledge of its maintenance will not complement the setup.

You will struggle to get any performance out of the outboard, and it will end up breaking down in due time.

Yes, you will have to hassle a lot with performance issues. This is one of the main reasons why you won’t see even the most loaded anglers avoid premium units. 

So, you might ask how to limit these issues? Well, you can limit them by learning the proper care requirements. You have to learn everything from the basic maintenance to filling up oil and much more.

Sounds easy right? Well, it isn’t. There are so many things that can go wrong, and you will have to keep track of a ton of factors to secure a suitable response from the outboard. 

You’ll need to examine the cooling system, power output, cleaning state, overheating problems, installation mistakes, and a lot more.

Can you do it on your own when you first start out? most likely not There is hence no need to waste your time.

We will encourage you to seek assistance from the authorities. They will greatly simplify your life and relieve you of trouble on your own.

One of the more frequent inquiries we’ve been getting recently is about the oil filling procedure. Owners are forced to use the bottom hole when adding oil to the outboard’s lower part.

Now, the issue with this bottom hole is that it creates a lot of mess. However, that doesn’t mean that it is not the right method. The purpose of filling up the oil from the bottom is to limit air bubbles.

Can You Fill Lower Unit Oil from Top? 

While it is possible to top off the bottom unit with the help of an additional tube, it is almost always better to stick with the bottom inlet to fill the oil in the lower section.

We recognize that trying to close the hole from the bottom would only make things worse for you. But you must go cautiously. If you just try to save time by making the situation more complicated, your system can suffer.

Without any additional equipment, it is rather difficult to avoid air pockets in the system while utilizing the top hole. A tube or syringe is required so that you may fill the bottom unit from the top.

You just have to turn off the unit’s power before using the tilt trim to completely drain the bottom unit of oil.

A container should be positioned under the outlet on the starboard side of the boat to prevent any more mess.

Once the oil has been taken out of the unit, you may replace the screw and depend on a lube pump to transfer the oil from the top hole into the bottom unit.


To get the oil into the bottom part of your outboard, utilize a tube with a tiny diameter. If not, you’ll have to deal with a lot of air pockets, and as the machine warms up a little, the oil will start to leak.

After a few pumps, the oil will begin to drip out of the top hole, coating the tube. Once the motor has been fully oiled, you may finish the operation by reinstalling the screw into the top hole.

Some fishermen also like using the tilt trim components to change the motor’s angle. In the end, the outboard will operate better since the superfluous air pockets in the oil are removed.

These actions may appear straightforward, but depending on the bottom hole to fill the section will provide far better results. Even if you completely follow these instructions, the air pockets in the oil compartment will cause issues.

However, this issue can be avoided by using a reliable oil pump in the lower section of your motor.

So, keep that in mind if you’re struggling with filling the oil in the lower unit. The lube pump will only cost a few bucks and will have a substantial impact on the final performance of your unit.

The brand and the model of the outboard have a huge impact on the servicing requirements. While the manual covers all serving the care requirements in extensive detail, it also helps to learn from a trained professional. 

In addition to saving time on outboard maintenance, you will learn a ton of new maintenance procedures by doing this.

Anglers often seem perplexed while changing the oil in the bottom unit from the top. The first time you add more oil to this gearcase, it can be difficult to operate. Therefore, spare yourself the trouble and just ask a local for assistance.

Should You Fill Lower Unit Oil From Top?

oil can

Now that you know how to fill lower unit oil from top, the question remains “whether or not you should fill the lower unit oil from top?”

Well, the answer here is not that simple and relies heavily on your skill. So, you should first perfect the technique if you’re not sure about filling up the lower unit.

Yes, using the tubes and the syringes will help you limit the air pockets and the bubbles inside the system, but they can’t help you eliminate them completely.

As you push the oil down into the system, the air pockets will start forming. 

There is still a potential that you may botch up the filling method, even if you are an expert and cautious. Therefore, we will always advise you to depend on the strategy that the dealer suggests rather than trying your luck.

Yes, changing the oil from the bottom will be more difficult for you. However, the outboard will respond much more quickly, and the system will work effectively for you.

Therefore, bear all of this in mind and take the time necessary to top up the oil from the bottom.

Will going through all of the additional trouble make you happy? Most likely not!

However, we can guarantee that after the oil has been changed, you’ll be pleased with how much better your boat performs. So, put up with the first discomfort; the outcomes will make up for it.

One more thing that you need to keep in mind here is that you can always limit the hassle. Yes, the procedure can be messy when you’re trying to access the hatch from the bottom. However, you can limit the mess and be more efficient. 

All it takes on your end is to learn the proper technique and method. So, be sure to rely on the locals and the experts living in your region. They will show you exactly how to get through the routine without creating too much mess.

Wrapping Up

Struggling with the oil changing routine for the lower unit on your boat? We’ve listed how you can fill the bottom unit with the top insertion.

While you’ll be able to get through the process without much hassle, we will still recommend against it.

Air pockets will develop within the system if the bottom unit is filled from the top, which will only lead to problems.

These air pockets will cause extra difficulty, and your unit’s performance will be, to put it mildly, substandard. Therefore, your only option is to use the correct strategy of starting from the bottom.

Is there a longer timeframe? Yes! When it comes to enhancing your regimen, you don’t have many alternatives.

Your only goals here are to reduce difficulty and ensure that the oil is loaded correctly and bubble-free. That ought to be plenty to have you taken care of here.

However, if you’re unsure about the proper method when it comes to filling up the bottom unit, try relying on guidance from a local expert. He will make your life much easier, and you will not have to hassle on your own. 

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