35 How To Bypass Oil Injection On Mercury Outboard

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Mercury outboard engines are known for their reliability and performance, but some boat owners prefer to bypass the oil injection system for various reasons. Whether you want to eliminate the risk of oil injection system failure or simply want to take control of your engine's lubrication, bypassing the oil injection system can be a viable option. In this article, we will guide you through the process of bypassing the oil injection system on a Mercury outboard.

What is oil injection?

Before we delve into the process of bypassing the oil injection system, let's first understand what oil injection is and why it is used in Mercury outboard engines. Oil injection is a system in which the engine's fuel and oil are mixed automatically during operation. This system eliminates the need for pre-mixing fuel and oil, making the engine more convenient to use. The oil injection system ensures that the engine receives the correct amount of oil for lubrication, improving its overall performance and longevity.

Reasons to bypass the oil injection system

While the oil injection system offers convenience and peace of mind for many boat owners, there are several reasons why some may choose to bypass it:

  1. Reliability: Some boat owners prefer to rely on traditional pre-mixing of fuel and oil to eliminate any potential failures or malfunctions in the oil injection system.
  2. Control: Bypassing the oil injection system allows boat owners to have full control over the oil-to-fuel ratio, which can be advantageous in certain situations.
  3. Performance: By bypassing the oil injection system, boat owners can experiment with different oil-to-fuel ratios to optimize engine performance.
  4. Maintenance: Removing the oil injection system simplifies the engine's maintenance process and reduces the chances of oil-related issues.

Tools and materials needed

Before you begin the process of bypassing the oil injection system on your Mercury outboard, make sure you have the following tools and materials:

  • Socket set - for removing bolts and screws
  • Wrench - for tightening and loosening nuts
  • Tubing and fittings - to redirect the oil flow
  • Plugs - to seal off any unused connections
  • Oil - for pre-mixing with fuel (if you choose to bypass the system)

Step-by-step guide to bypass oil injection on Mercury outboard

Step 1: Prepare your workspace

Start by ensuring that your workspace is clean and well-organized. Having a clutter-free environment will make the process easier and more efficient. Lay out all the tools and materials you will need for the job.

Step 2: Locate the oil injection system

Refer to your Mercury outboard engine's manual to locate the oil injection system components. Generally, the oil injection system consists of an oil reservoir, oil pump, and oil lines. Familiarize yourself with the system before proceeding.

Step 3: Drain the oil reservoir

Before bypassing the oil injection system, drain the oil reservoir completely. This will prevent any residual oil from contaminating the engine or fuel system during the bypass process.

Step 4: Disconnect the oil lines

Using a wrench or socket set, carefully disconnect the oil lines from the oil pump and engine. Be cautious not to damage any components during this process. Cap off the disconnected oil lines to prevent any oil leakage.

Step 5: Remove the oil pump

Once the oil lines are disconnected, remove the oil pump from the engine. This step may require the use of a socket set or wrench, depending on the mounting method of the oil pump. Set aside the oil pump for future use or disposal, depending on your preference.

Step 6: Install tubing and fittings

In order to redirect the oil flow, you will need to install tubing and fittings. Measure and cut the tubing to the appropriate lengths, ensuring a proper fit between the disconnected oil lines. Use fittings to secure the tubing in place, providing a leak-free connection.

Step 7: Connect the tubing

Connect one end of the tubing to the oil pump outlet and the other end to the engine's carburetor. Make sure the connections are secure and properly tightened to prevent any oil leakage. Double-check all connections before proceeding.

Step 8: Seal off unused connections

If there are any unused connections or openings on the engine or oil reservoir, seal them off using plugs. This will prevent any potential oil leaks or contamination.

Step 9: Pre-mix fuel and oil (optional)

If you choose to bypass the oil injection system completely, you will need to pre-mix fuel and oil in the correct ratio. Consult your engine's manual for the recommended oil-to-fuel ratio and ensure thorough mixing before refueling your boat.

Step 10: Test the bypassed system

Once you have completed the bypass process, it is crucial to test the system before operating your boat. Start the engine and observe the oil flow through the tubing. Ensure that there are no leaks and the engine performs as expected.


Bypassing the oil injection system on a Mercury outboard engine can provide boat owners with more control, improved reliability, and the ability to fine-tune engine performance. However, it is important to note that bypassing the oil injection system may void certain warranties or require additional maintenance. Before proceeding with the bypass process, consult your engine's manual and consider seeking professional advice if needed. With the right tools, materials, and careful execution, bypassing the oil injection system can be successfully accomplished.