🕐 Read time: 5–6 minutes

Keeping your marine engine free from salt and corrosion is one of the most important jobs for any boat owner. In this guide, we’ll walk you through the full process of using Boatworld Blu Thru flushing tablets to keep your engine in top condition. Whether you run an outboard, an inboard, or a PWC, this article gives you all the details you need to flush your engine like a pro.

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• ⬇️ Jump to a section in this guide:
  
• Flushing an Outboard with Muffs
  
• Flushing an Outboard in a Container
  
• Flushing a Stern Drive
  
• Flushing an Inboard Engine
  
• Flushing a PWC / Jetski
  
• Key Safety Checks
  

Flushing an Outboard with Muffs

This is the most common method for flushing an outboard. It's fast, efficient, and requires minimal equipment.

1. PREPARE THE ENGINE
   Tilt the engine fully down into its vertical running position. Place the flushing muffs securely over the water intake vents, ensuring a tight seal.
2. CONNECT THE FLUSHING SYSTEM
   Unscrew the mixer cup, add the recommended Blu Thru tablets, and screw it back on tightly. Set the mixer dial to ‘RINSE’, then connect your garden hose to the mixer inlet and the muff's hose to the mixer outlet.
3. TURN ON WATER & START ENGINE
   Turn the tap on fully. With water flowing from the muffs, start the engine and let it run at idle speed. Immediately check for a steady stream of water from the tell-tale outlet.

❗ Key Detail: The "tell-tale" is the small stream of water ejected from the engine. It's your visual confirmation that the water pump is working and water is circulating correctly.

⚠️ Warning: If no water appears from the tell-tale within 15 seconds, shut the engine off immediately and check your connections. Running an engine dry will cause serious damage.

4. ACTIVATE BLU THRU
   Turn the mixer dial to ‘SOAP’. Wait for the tell-tale stream to turn blue, and then continue to run the engine until the water turns clear again.
5. FINAL RINSE
   Turn the dial back to ‘RINSE’ and run the engine for 2 more minutes to flush the system completely.
6. SHUT DOWN
   You can now remove the muffs.

⚠️ Warning: The shutdown sequence is critical. First, turn the engine off. Immediately after, turn the water off.

Flushing an Outboard in a Container

A great alternative if you don't have muffs, especially for smaller engines.

1. PREPARE THE SETUP
   Place a large container under the engine and lower the motor into it. Fill the container with fresh water until the level is several inches above the water intakes. Add the recommended amount of Blu Thru tablets to the water.
2. RUN THE ENGINE
   Start the engine and run it only at a slow idle speed. Once water is flowing correctly, let the engine run for 5-10 minutes to circulate the solution.

⚠️ Warning: Ensure the engine is and remains in NEUTRAL at all times. A spinning propeller in a container is extremely dangerous.

⚠️ Warning: If no water appears from the tell-tale within 15 seconds, shut the engine off immediately.

3. SHUT DOWN AND DRAIN
   Turn the engine off completely. Tilt the engine up and out of the container, allowing all water to drain out of the cooling system.
4. FINAL RINSE
   Give the exterior of the outboard a quick rinse with fresh water from a hose to remove any remaining salt solution.

Flushing a Stern Drive

The process for a stern drive is very similar to an outboard, using flushing muffs to supply fresh water to the outdrive.

1. PREPARE AND CONNECT
   Tilt the outdrive fully down to its vertical position. Securely attach the flush muffs over the water intake vents. Load the Blu Thru mixer with tablets and connect your hose system. Set the mixer dial to ‘RINSE’.
2. START WATER AND ENGINE
   Turn the tap on fully. Immediately start the engine, keeping it at idle in neutral. Check the stern to confirm water is flowing from the exhaust ports.

⚠️ Warning: If no water appears within 15 seconds, shut the engine off immediately and check all connections.

3. ACTIVATE BLU THRU
   Turn the mixer dial to ‘SOAP’. Watch the exhaust water until it turns blue, then continue running the engine until the water runs clear again. Once clear, turn the mixer dial back to ‘RINSE’ and let the engine run for two more minutes.
4. SHUT DOWN

⚠️ Warning: The shutdown sequence is critical. First, turn the engine off. Immediately after, turn the water off.

Flushing an Inboard Engine

Flushing an inboard involves using the boat's own raw water system to circulate the cleaning solution.

1. CLOSE THE SEACOCK
   Close the seacock for the engine's raw water intake.

⚠️ Warning: This step is crucial to prevent your boat from taking on water while the system is open.

2. PREPARE THE SEA STRAINER
   Open your sea strainer, remove the filter basket, and clean out any debris.
3. ADD BLU THRU TABLETS
   Place 8 Blu Thru tablets into the empty strainer basket and put the basket back into its housing.
4. INTRODUCE FRESH WATER
   Place a freshwater hose into the open strainer housing and provide a steady, medium flow of water.

❗ Key Detail: Do not use high pressure, as this can overflow the strainer. The engine only needs a gentle, continuous supply.

5. RUN THE ENGINE
   With fresh water flowing, start the engine and let it idle for 5-10 minutes. You will see blue-tinted water exiting the exhaust.

⚠️ Warning: Never run the engine without a water supply, as this will quickly damage the raw water pump impeller.

6. COMPLETE THE SHUTDOWN
   Securely replace the strainer lid and, finally, re-open the raw water seacock.

⚠️ Warning: The shutdown sequence is critical. First, turn the engine off. Immediately after, turn off the freshwater hose.

Flushing a PWC / Jetski

Keeping your PWC’s high-performance engine clean is vital. Pay close attention to the unique start and stop sequence to avoid flooding the engine.

1. PREPARE & CONNECT
   Position your Jetski on a level surface. Open the Blu Thru mixer canister, place four (4) Blu Thru tablets inside, and screw it back together securely. Attach the mixer to your garden hose and set the dial to ‘RINSE’. Now, attach the correct flush adapter and firmly connect the entire assembly to the PWC's flush port.
2. START THE FLUSH SEQUENCE

⚠️ Warning: The PWC start sequence is vital to protect your engine. First, start the PWC engine. Immediately after, turn on the water.

3. ACTIVATE BLU THRU
   Once water is flowing correctly from the exhaust, turn the mixer dial to ‘SOAP’. Let the engine run for 3-5 minutes until the water, which will turn blue, runs clear again.
4. SHUT DOWN
   Once the engine is off, you can disconnect the hose and adapter.

⚠️ Warning: The PWC shutdown sequence is just as important. First, turn off the water. Immediately after, stop the PWC engine.

Key Safety Checks

• Always Confirm Water Flow: No matter your engine type, always get visual confirmation that water is circulating before letting the engine run for more than a few seconds.
• Follow the Shutdown Sequence: The order in which you turn off the engine and water is critical. Get it wrong, and you risk severe engine damage. PWCs are water off first; most other engines are engine off first.
• Never Run Dry: An engine's water pump impeller can be destroyed in seconds without water for lubrication and cooling.

💡 Pro Tip: Get into the habit of flushing your engine after every use in salt water. It’s the single best thing you can do to extend its life and ensure reliable performance.

Want to Learn More?

For more tips, guides, and to get your own Blu Thru tablets, check out the links below: