Not hitting WOT RPM

[adammcmanus]

Hi,

2000 Bayliner 4087

Twin Cummins 6BTA 5.9 270 (300hrs on engines, previous owner hardly used it)

Engine Serial Numbers
Starboard: 45708033
Port: 45710278

Pleasurecraft; weekends and 2 week holidays. ~50hrs a year.

The issue I am trying to solve is why I am not getting WOT of >2600 when loaded to bear. When I first purchased the vessel, last year, it would get 2750 WOT RPM. I then motored the boat home to Georgian Bay in Ontario, Canada from Washington, DC. Near the end of our journey, I noticed our WOT RPM had dropped to 2500. And top-end speed had also dropped from ~26mph to ~23mph. So far I have tried (in this order) changing the fuel filters, cleaning the air filters, and having the props fixed. The prop shop did mention props were 70% and 30% out of shape from original state. We did hit a few dead-heads coming up the Hudson river, which was the reason we took them to the prop shop. Although the props were not in their original shape, the prop shop felt that their state would not cause the drop in RPM.

Last week I changed the off-engine and on-engine fuel filters. I now have new Baldwin 1281 fuel filters off-engine and Fleetguard 5285 on-engine. While doing so I also added a little bit of Seafoam to the on-engine fuel filters, with hopes of cleaning the injectors as much as possible.

After changing the fuel filters, WOT RPM at dock in neutral is 2900 for both port and starboard engines. Out on the water WOT RPM I get 2500 on both engines. Still 200 RPM short of target.

Thanks in advance for any insights or suggestions on what fixes to try next.

Adam

Topic

[adammcmanus]

I did check the linkage and fuel solenoid for full travel, no apparent issues there. The remaining items I am not able to check myself due to lack of tools and/or expertise. If those checks and aftercooler cleaning are the next steps, I guess it’s time to hire a mechanic.

Thanks Rob

[Rob Schepis]

Yes.

Green arrow = Aftercooler
Red arrow – Intake air grid heater

[Stephen Oliver]

These are the JWAC ones aren’t they? Trapezoidal shape at the top…

Steve

[glenn111]

Don’t see any aftercoolers.

[Rob Schepis]

So you had the expected rpm drop after loading the boat heavy. But then rpm’s continued to drop…

There are several important checks in that article that you never mentioned addressing – fuel pressure, linkages, lift pump, return line, etc…. Fuel supply valve accidentally bumped or creeping closed..

Although you claim not to see any smoke at cruise, etc it would be prudent to have the aftercooler ultrasonic cleaned to be sure the air side is clean and clear.

[adammcmanus]

Hi Rob,

When the boat was sea trialed early last year down in Washington, DC, the surveyor noted top RPM of 2750 at 26 mph. The fuel tanks were 1/2 full, not sure of water tanks. There were 2 guys on board. When we left Washington, DC with 5 guys, 1k worth of groceries, full fuel tanks, full water, dingy on the back, we were getting 2650 WOT RPM. The load at that time was greater than what I would consider as my normal ‘fully loaded’ boat.

Yes, I have gone through https://www.sbmar.com/featured-article/understanding-low-power-troubleshooting/

We have no smoke at idle, cruise or WOT.

[Rob Schepis]

adammcmanus wrote:

When I first purchased the vessel, last year, it would get 2750 WOT RPM.

When exactly did you get the 2,750? When she was in “for sale” mode and stripped down of all gear, fluids, etc? Or did you continue to get the 2,750 after she was loaded for bear?

Smoke or no smoke?

Have you gone through this: https://www.sbmar.com/featured-article/understanding-low-power-troubleshooting/

[adammcmanus]

Pics of engines and prop scans

Here are some pics of my engines and prop scans done before and after props were fixed.

[Author]

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