Lost 500 RPM after 30 min WOT R21EC Yanmar 3YM30

C

ClearwaterMike

Member
Joined
Jan 17, 2019
Messages
19
Fluid Motion Model
C-24 C
2013 R21EC, Yanmar 3YM30, 198 hours. Max RPM 3300 in water, but experiences loss of RPM and speed after 20-30 minutes. This is a new problem, as it was operating fine last month. WOT 3300 and 8.5 to 9 MPH.
Issue:
Running Wide Open Throttle (WOT) for 20-30 min, engine RPM drops from its max RPM of 3300 to 2800rpm. once I throttle back and run for 2-5 min at 2100RPM, then throttle back up, engine then provides 3300RPM, but steadily drops back down to 2800. max speed at this rate is 6.8 mph.

Done so far: Drained and Removed fuel tank, visually inspected inside of tank (clean), reinstalled, all new fuel. Checked and cleaned breather (line, screen) - ok. checked and inspected flexible pick-up line and screen strainer, - clean and line has plenty of flow. All lines including fuel return lines evacuated, and air can easily be pulled and blew through. Fuel filter on engine replaced. system primed, no air in system. Problem persists. Fuel and fuel system ruled out?

Another note is that if continued to run at WOT even at 2800RPM the smell of diesel exhaust is overwhelming, no black smoke exiting the exhaust. Checked all hoses, no leaks.

Boat runs fine at 2200 RPM, max speet is 6.8mph
 
Did you replace both fuel filters, or just the secondary one on the engine?
 
Exhaust ? White smoke/steam or black ? Do you have good raw water flow out exhaust?
 
no smoke, white or black. the water comes out in spirts, higher RPM its more of a spirting spray


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Mike
You said no black smoke, if your getting steam/white and the smell of diesel fumes, I would suspect the raw water system! After running at 3000rpm for 30 min your engine would start to overheat and loose power, just my uneducated option. Bob
 
First thing to check is water pump (impeller)
Second is the exhaust elbow (that's where I would put t my money if I was betting!)
 
Looking in the sailing forums on this exact issue say its “usually the exhaust elbow”, apparently a consumable item. not that expensive tomorrow’s project!


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ill replace the impeller too, a good time to start the maintenance clock


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Elbow replaced, Overdue for replacement!

Here is what it looked like:
9h83dg.jpg

23rjne0.png


Here is the New One:
jkag42.png
 
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