Lower Units

Why is Your Outboard Lower Unit Making Strange Noises?

Are you hearing alarming noises coming from your outboard lower unit? If so, it’s essential to take note and take action. Understanding the cause of strange noises and adequately addressing the problem is necessary for your boat’s ongoing health and performance. This blog will explore some of the most common causes of strange noises from outboard lower units. And what you can do to get your boat running smoother and safer. Join us as we dive into why your lower unit is making unexpected and strange noises and how to solve the issue.

Causes of Strange Noises in Outboard Lower Unit

Strange noises from outboard sei lower units can create confusion, fear, and frustration for boat owners. After all, your outboard lower unit contains many components necessary for propelling your boat, so when something goes wrong, it’s a problem. But what’s causing the strange noise?

Here are some common causes of strange noises in the outboard lower unit, such as:

Worn Bearings:

Worn bearings are one of the most common causes of strange noises in an outboard lower unit. Your outboard lower unit contains numerous bearings that allow the engine and propeller shaft to rotate smoothly. Over time, these bearings can wear down and lose their efficiency, resulting in strange noises while the engine runs. If left unchecked, this can lead to significant damage due to friction.

Damaged Gears:

Another common cause of strange noises in outboard lower units is damaged gears. If a gear has become damaged, it can result in poor meshing, skipping, or grinding noises. If the gears have worn or been stripped, you may also hear metallic or buzzing sounds from the lower unit. 

Leaky seals

Leaky seals constitute a significant problem for outboard lower units and can be the source of some weird noises and other issues. A pressure buildup or a crack in the seal will eventually allow air and water to enter the lower unit. This will lead to strange noises as the crankcase valves move and can even lead to engine operation problems. If you believe the seal is the culprit, the best action is to check it for any signs of cracking or tears and replace it as needed.

Clogged water pump

Another common cause of strange noises in the outboard lower unit is a clogged water pump. When the pump gets too dirty or degenerates, it can create serious issues. A messy, clogged pump hinders water flow within the motor, leading to all sorts of weird noises, as well as more severe problems. The best solution here is to take out the pump and look at it, thoroughly cleaning if needed and replacing it if it’s too damaged.

Propeller Issues

One of the common causes of strange noises in an outboard mercury lower unit is a propeller issue. The propeller on your outboard motor needs to be correctly sized and balanced for regular operation. Any faults with the propeller, such as incorrect size or balance, can lead to abnormal vibration or noise from the lower unit.

In addition, if the propeller has any damage, such as a crack or a nick, it can cause an irregular rotation, resulting in strange noises. If you believe that the propeller is the source of the noise you hear, it’s essential that you take it to a specialist to have it inspected and, if necessary, replaced. 


Overheating is another major cause of strange noises in outboard lower unit mercury. If your outboard motor is running too hot, you may hear strange squealing and whining noises coming from the lower unit. This usually occurs when the water is not circulating correctly, causing the bearings in the lower unit to become overheated. If you believe that the lower unit is running too hot, you should check the water pump impeller to ensure that it is intact and free of debris. You should also check the intake holes to make sure they are clear, and if necessary, consider replacing the impeller.

Solving the Problem

Have you heard strange noises from your outboard lower unit and have no idea how to fix the problem? We have some tips that could help you get started in solving the issue. 

Replacing Worn or Damaged Parts

The most common reason for strange noises coming from the outboard lower unit outboard is worn or damaged parts. Worn-out and damaged seals and bearings can create a whine or a clicking sound, as well as a rattling or clattering. The transmissions and gears can seize or grind, producing a range of odd, tinny sounds. Fortunately, the good news is that damaged parts can be replaced with relative ease, putting the outboard lower unit back into working order and restoring your peace.

Lubricating and Maintaining the Unit

Lower unit problems are a common issue for boat owners. From whining to squealing, strange noises from the lower unit can be a real nuisance. Luckily, lubricating and maintaining the outboard lower unit is one of the easiest ways to solve this problem.

For starters, it’s essential to regularly check and replace the gearcase oil in your outboard lower unit. This will help ensure that your unit receives the right amount of lubrication, which is essential for a healthy lower unit. Also, replacing the gear oil will keep any metal shavings and dirt from building up, which can lead to wear on your unit and increase noise levels.

Flushing The Water Pump

Flushing the motor’s water pump is an effective and relatively simple way of solving noise or lower unit heating issues. The process is relatively quick and can do with a garden hose. Start by connecting the hose to your outboard and then hooking the other end to a running faucet. Next, let the water run for a few minutes; this will flush out any dirt or debris trapped in the pump. Be sure to monitor the temperature of the water as it runs, indicating whether the pump is working correctly. Finally, shut off the water, disconnect the hose, and test your outboard to see if the strange noises are gone. 

Tuning the Engine

Another way to address the noisy lower unit is to tune the engine. An engine tune-up, though more time-consuming, is an effective way to diagnose and eliminate unseen problems. Start by checking and replacing the spark plugs. Consider taking your outboard to a professional if you feel uncomfortable doing this. From there, inspect the fuel line, filter, and carburetor to ensure no blockage or other problems. Finally, check to ensure the oil and air filter are clean, and then have a professional run a compression test to ensure optimum performance. 

Replacing or Adjusting the Propeller

If you hear strange noises from your outboard lower unit propeller section, you may need to replace or adjust the propeller. Often, strange sounds can be due to the propeller being out of balance or not the correct size. Replacing or adjusting the propeller is often the best solution to solving this problem, ensuring your outboard runs smoothly and safely while improving its overall performance.

Preventative Measures to Avoid Strange Noises in the Future

Regular maintenance and proper storage are two of the most effective preventative measures to avoid strange noises coming from an outboard lower unit in the future. Simple checks such as regularly cleaning and lubricating the unit, ensuring the engine keeps cool, and using the right propeller can help reduce the chances of noises occurring. Moreover, if the engine has been sitting idle for a while, flushing the unit with fresh water, replacing any corroded components, and topping off all the fluids and lubricants mentioned earlier, should be done. Taking the time to maintain and store the unit properly may save many headaches, including those associated with strange noises outboard the lower unit.

Final Thoughts

Several issues, including loose bolts, worn-out water pumps, and bent propellers, can cause strange noises from your outboard lower unit. Addressing these issues as soon as possible is essential to avoid further damage, which can lead to costly repairs. Remember what we shared above, or consult a professional marine mechanic if you have any questions or concerns about your outboard motor.