Testing Boat Wide Open Throttle: A Step-By-Step Guide

Wide-open throttle (WOT) is a topic that strikes fear into the hearts of many boat owners, with some reluctant to push their boats to the limit. However, engine manufacturers do not share this view, and running at WOT can actually offer several benefits. Firstly, it can ensure that the engine warranty remains valid, as some manufacturers require the engine to reach WOT to maintain the warranty. Secondly, WOT allows access to the engine's maximum power, which may be crucial in emergency situations. Additionally, running at WOT can reveal issues that might be masked at lower RPMs, providing a valuable stress test for the engine. It also establishes a baseline for monitoring the engine's performance over time and can help with carbon buildup. While there are valid concerns about potential engine damage, following the manufacturer's guidelines and consulting a local mechanic can help strike a balance between fuel economy, reliability, and longevity.

Check the throttle control advances the throttle lever on the engine from stop to stop

To test boat wide-open throttle, it is important to ensure that the throttle control advances the throttle lever on the engine from stop to stop. This means that the throttle lever should be able to move from the minimum to the maximum position.

To check this, first locate the throttle lever on the engine. This is usually found in the cockpit or dashboard of the boat. Next, with the engine turned off, advance the throttle lever from the minimum to the maximum position. On the engine, you will find a place where the cable attaches, and there should be a lever that travels from one stop to another. This lever should hit both stops. If it does not, the linkage may need to be adjusted.

Proper throttle control adjustment is crucial for the safe and efficient operation of your boat. It ensures that you can access the full power of the engine in case of an emergency and helps to prevent issues such as engine overheating. Additionally, it provides a valuable baseline for monitoring the engine's performance over time.

It is worth noting that different engine manufacturers have different recommendations for running at wide-open throttle. For example, John Deere suggests running at full power for no more than 30 minutes out of each eight hours, while Cummins recommends infrequent use of full power for only one hour out of every eight hours. Always refer to your engine's specific guidelines for safe operation.

Running at WOT can reveal issues masked at lower rpm

Running at wide-open throttle (WOT) can reveal issues masked at lower rpm. If the engine is unable to reach WOT, it indicates that there may be underlying problems that need to be addressed. For instance, a boat owner may discover that their engine is unable to reach maximum rpm due to a faulty throttle control or linkage issue. This can result in reduced power and affect the overall performance of the boat.

Additionally, running at WOT can be used as a "stress test" to identify potential engine health issues. If the engine overheats at maximum rpm, it suggests that the system is marginal and requires attention. Other problems, such as restrictions in the air or fuel supply or increased drag caused by a fouled bottom or propeller, may also become apparent during a WOT test.

Conducting a WOT test provides a valuable baseline for monitoring the engine's performance over time. By repeating the test at a later date, boat owners can identify any changes in rpm, speed, or temperature, which may indicate potential maintenance issues.

It is important to note that WOT tests should be conducted within the specified time frames recommended by the engine manufacturers. While occasional WOT operation can improve reliability and provide performance benefits, excessive or prolonged use may lead to increased fuel consumption and reduced engine longevity.

Running at WOT provides a valuable baseline to monitor the engine's performance

Running at wide-open throttle (WOT) can provide a valuable baseline to monitor the engine's performance. This is because the WOT rating established by the manufacturer serves as a benchmark of a healthy engine. By running the engine at WOT, you can determine if there are any underlying issues or problems that need to be addressed. For example, if the engine overheats at WOT, it indicates that the cooling system is not functioning optimally and requires attention.

Repeating the WOT test at a later date can help identify any changes in the engine's performance. For instance, a decline in RPM or speed, or an increase in temperature, could indicate a decline in engine health. Running at WOT can also help identify issues with the propeller, such as incorrect size, pitch, or number of blades, which can impact fuel economy and overall engine performance.

Additionally, WOT testing can reveal latent defects in the engine or its associated systems, ensuring that the engine will operate reliably. It is important to remember that even if you never intend to operate the engine at WOT, ensuring that it can achieve this RPM is critical. It confirms that the propeller is properly matched to the engine and that the overall installation is sound.

WOT testing can also provide peace of mind in emergency situations. By occasionally running the engine at WOT, you can be confident that the engine can deliver full power when needed. It is recommended to refer to the engine manufacturer's guidelines and consult a local mechanic for recommendations on how often and for how long to run the engine at WOT.

Check the accuracy of the tachometer and the full travel of the throttle

Checking the accuracy of the tachometer and the full travel of the throttle is crucial to ensure the proper functioning of your boat's engine. Here's a detailed guide to help you through the process:

Checking the Tachometer Accuracy:

• Understand the Importance: An accurate tachometer reading is essential to ensure your engine is performing optimally. It helps you avoid overloading the engine before it warms up and prevents under-loading after warm-up. It also assists in determining fuel burn, checking prop size, and identifying early signs of potential issues.
• Recognize Potential Inaccuracies: Tachometers can drift over time, especially if you've upgraded to a larger alternator or switched to a serpentine belt. These changes can affect the number of pulses per revolution, leading to inaccurate readings.
• Invest in a Handheld RPM Counter: Handheld RPM counters are affordable and provide accurate readings. They can help you verify the actual RPM of your engine.
• Recalibrate the Tachometer: Once you have the accurate RPM reading, you may need to recalibrate the tachometer. This process can be time-consuming, but it's worth ensuring accuracy. Refer to the calibration instructions for your specific tachometer model, which are usually available online.
• Alternative Method: You can also use a smartphone app to check tachometer accuracy. Paint a white line on the spinning part of the engine and use the app to flash a strobe at the spinning part. Adjust the strobe speed until the white line appears stationary, and the strobe frequency will give you the accurate RPM.

Checking the Full Travel of the Throttle:

• Understand the Throttle Linkage: Before troubleshooting, ensure that the throttle control at the helm advances the throttle lever on the engine from stop to stop. This linkage is crucial for the engine to receive the full-throttle message from the helm.
• Inspect the Throttle Lever: With the engine off, have someone advance the throttle from minimum to maximum. Locate the point where the cable attaches to the engine. There should be a lever that travels from one stop to another, hitting both ends.
• Adjust the Linkage if Needed: If the lever does not hit both stops, the linkage may need adjustment. Proper adjustment ensures that the engine receives the correct full-throttle signal.
• Test the Throttle in Neutral: Momentarily run the throttle up to maximum in neutral. This won't harm the engine and will help rule out issues like an oversized or fouled propeller. If the engine reaches the rated high idle RPM, the problem is not in the throttle control.

By verifying the accuracy of the tachometer and the full travel of the throttle, you can ensure that your boat's engine is performing as expected and address any potential issues early on.

Check the engine's cooling system

Seawater Cooling System

Also known as a raw water cooling system, this system uses the water that the boat is floating in to cool the engine. It makes no difference whether the water is salt or fresh. The process starts by drawing water into the engine through a seacock fitting and pumping it through the engine's water jacket and ports by way of a mechanical water pump. The water flows through the engine and directly out the exhaust.

To check this system, first ensure that the seacock shut-offs are operable by testing them monthly. As a backup, you should have a soft, tapered, wooden plug (called a bung) of the size of the seacock tied to the seacock. Next, check the sea strainer for any debris, sand, leaves, etc. and clean or replace the filter or screen if necessary.

Freshwater Cooling System

Also known as an enclosed cooling system, this system uses a small tank on the top of the engine that contains a combination of freshwater and coolant. The freshwater is circulated through the engine and through a heat exchanger. The raw water is pumped through the heat exchanger where it absorbs some of the heat from the freshwater before being pumped out the exhaust.

To check this system, first ensure that the coolant is diluted correctly with water. The proportions are critical: too little coolant will result in corrosion, and too much will degrade its ability to absorb heat. Next, check the sacrificial anodes, or zincs. These are designed to corrode and dissolve so that other, more expensive, engine components do not. Replace any anode that is more than half gone or showing any visible deterioration.

Integral Pump

Inboard engines have an integral pump, usually on the front of the engine and driven by a belt, to ensure the coolant circulates properly. This pump typically has a long life and requires no servicing.

Raw Water Pump

All engines also have a second pump to circulate raw water. On outboards, it is usually in the midsection, and on inboards, it is typically on the front of the engine. This pump has a limited service life, especially if the boat has been operated in a sandy environment.

You can replace the rubber impeller annually or leave it alone until there is a problem. The impeller can be difficult to install, and doing it incorrectly will almost certainly cause overheating. Before they fail, water pumps usually give some warning, such as reduced water flow out of the exhaust or rising operating temperature.

Drive Belts

Finally, check the drive belts. It is rare, but not unheard of, for a belt to break. A more likely problem is glazing, which is a shiny surface on the interior side of the belt due to slippage. A glazed belt cannot be repaired and will continue to slip until the engine overheats, so replace it and make sure the tension is correct.

Frequently asked questions