CONTINUOUSWAVE

The 2008 Mercury VERADO 200-HP engine on my [unspecified model year] 200 DAUNTLESS has run perfectly for 550-hours, and accelerates the boat onto hydroplane rapidly and then accelerates the boat to a speed greater than 50-MPH.

Around August 10, 2024 (about three weeks ago) I heard a whistle noise coming from the 2008 VERADO 200-HP engine. I thought [the source of the noise was due to propeller] cavitation occurring because the engine trim was improper.

The around August 17, 2024 (about two weeks ago) I had "a few" people onboard the boat with the weigh distribution spread evenly from bow to stern, and the 2008 Mercury VERADO 200-HP could NOT accelerate the boat onto hydroplane, and the engine could not accelerate to more than 2,800-RPM. Then I moved all the passengers to the forward part of the cockpit to get the boat on plane. With the new weight distribution the engine was then able to accelerate to 4,000-RPM, and the boat speed increased to the point where the boat was on plane.

After that experience, I took the boat to a local mechanic [to look for the cause of the reduced boat speed]. The local mechanic said the 2008 VERADO 200-HP engine was in great condition. The mechanic connected a computer to the engine. The mechanic did find that there were any service codes stored in the engine. The mechanic did not find and mechanical defects in the engine.

Later, sometime in late August 2024, I took out the boat with only me aboard. The engine was still only able to accelerate to 4,000-RPM until the boat achieves plane, and with the boat on plane the engine speed increases above 4,000-RPM [to some unspecified maximum engine speed], the time from acceleration to being on plane was excessively long [compared to prior operation of the boat].

Further, in my test with only me aboard, even though the engine eventually accelerates to its normal full-throttle engine speed, the boat speed at that engine speed is 10-MPH to 12-MPH slower than the normal boat speed at engine full-throttle.

Around September 21, 2024 (about three weeks from now) I have an appointment to get the boat and engine looked at by a certified Mercury mechanic.

Q1: what could explain the behavior of the 2008 Mercury 200-HP engine that I have described above.

Q2: what will the repair cost be?

I am the second owner [of this unspecified model year] 200 DAUNTLESS, and I have all records of maintenance since the boat was new in the form of a hand-written log book by the previous owner. This boat has received meticulously care.

I have an idea that [the cause of the decreased performance of the engine is due to at some point in my operation of the boat] something was sucked up into the drive shaft. I do not know how [something being sucked up into the drive shaft] would cause a restriction in the engine speed

I will appreciate any explanations for the reduced performance of the 2008 Mercury VERADO 200 engine.

Your Verado is supercharged. The supercharger forces air into the cylinders at higher than atmospheric pressure. The noise you hear COULD be from supercharged air leaking to the atmosphere. Run the engine with the cowling removed to see if an air leak can be easily detected. If a leak is detected see if it is in an obvious place. It could be something as simple as a failed hose connection.

JollyWhaler wrote:Around August 10, 2024 (about three weeks ago) I heard a whistle noise coming from the 2008 VERADO 200-HP engine. I thought [the source of the noise was due to propeller] cavitation occurring because the engine trim was improper.

Propeller cavitation occurs under water and would not be heard as a whistle noise. Propeller cavitation occurs typically on the blade edges of a propeller. Unless you were listening to the propeller sound using a sophisticated SONAR with an audio output, you would not hear a noise from cavitation of the propeller blades.

Perhaps you are thinking of propeller ventilation, something much different that propeller cavitation. Cavitation occurs when air is sucked down into the propeller from operating the propeller too close to the water surface. Ventilation is also accompanied often with engine exhaust via the propeller hub breaking through to the surface instead of staying under water, and particularly so if the engine is trimmed out unusually far so the propeller thrust is being directed upward instead of astern.

For more about the difference between cavitation and ventilation of a propeller, see
https://uk.boats.com/how-to/propeller-c ... ntilation/

JollyWhaler wrote:I have an idea that [the cause of the decreased performance of the engine is due to at some point in my operation of the boat] something was sucked up into the drive shaft.

The water intake for an outboard engine has a screen that limits the ingress of any solid material. The path of cooling water into the engine from the water pick-up is to the water pump. After the water pump the water flows through the engine block in cooling passages. The water from the water pump never enters the engine drive shaft. When the drive shaft travels from the power head to the gear case, it will be in the midsection and leg, which generally is somewhat open and often has a shower of cooling water spraying on the interior to help keep the area cool from the hot exhaust gases that are also routed in that area.

If your reference to "drive shaft" was meant to mean the propeller shaft, the hub of the propeller is continually expelling exhaust gas and cooling water, so there is no chance for any suction of something in the water into the propeller hub.

Jefecinco wrote:Your Verado is supercharged. The supercharger forces air into the cylinders at higher than atmospheric pressure. The noise you hear COULD be from supercharged air leaking to the atmosphere. Run the engine with the cowling removed to see if an air leak can be easily detected. If a leak is detected see if it is in an obvious place. It could be something as simple as a failed hose connection.

Thank you! [A leak of supercharger air] was the [cause of the] problem [and created the whistling noise].

I took off the [engine] cowling and immediately saw the upper boost pipe was loose and worn. I bought a replacement part, installed i, and took the boat out for a test drive: acceleration and top speed were both back.

Butch--you are a lifesaver.

JollyWhaler wrote:Butch--you are a lifesaver.

Also, I think Butch is a money saver, as having a marine mechanic diagnose and remedy that problem would have cost much more than Butch charged you and this forum charged you for getting a good hint about where to look for the cause of the whistling and reduced engine performance.

jimh wrote:

JollyWhaler wrote:Butch--you are a lifesaver.

Also, I think Butch is a money saver, as having a marine mechanic diagnose and remedy that problem would have cost much more than Butch charged you and this forum charged you for getting a good hint about where to look for the cause of the whistling and reduced engine performance.

You couldn't be more correct Jim! And thank you for your explanation on a few terms I had mixed up. I certainly have a lot to learn on the in's and out's of outboard terminology and engineering, but your posts were very helpful in furthering my understanding of their mechanics. It's very much appreciated.

Heya J-Whaler: you are very welcome. The goal of this website has always been and continues to be to collect information, organize that information, and keep it on-line for as long as possible (so far over 25-years) so people l can find it and read it at no cost.

I am curiousL

Q3: how much was the replacement part as an OEM part from Mercury Marine?

Q4: was the replacement part a molded plastic pipe or assembly or a flexible hose?

jimh wrote:Q3: how much was the replacement part as an OEM part from Mercury Marine?

The kit I bought from USP Marine was $189 and included both the long pipe and the smaller coupler. The only OEM part I was able to find online was $118, and it was a stiff plastic hose and did not include the smaller coupler (included in the USP Marine kit).

jimh wrote:Q4: was the replacement part a molded plastic pipe or assembly or a flexible hose?

Both the OEM and USP Marine parts are aluminum pipes wrapped in a wired mesh and silicon outer layer. The USP Marine kit also came with stainless steel, reusable clamps to replace the aluminum one-time use clamps from the OEM part.

Thank you for the very thorough answer to my questions.

My general inference regarding after-market replacement parts: if after-market replacement parts exist for a very specialized OEM part, there probably is a strong market for those parts, that is, these unusual parts are often needed for repairs for the product, and in some cases the after-market part maybe superior to the OEM part, as seems to be the case here.