Cooling problem...

[Old Master]

I have a 2005 R21, 3-cyl 20 HP Yanmar (of course.) Last fall my cooling alarm went on. I cut off the engine for awhile and opened the motor cover. It started okay, so I steamed back to port at dead slow. Took it to a mechanic, who "flushed the system," and changed the impeller, telling me it had a couple of broken blades.

Took it out again, same thing happened. So, filters are clean, system is flushed out, new impeller, but alarm comes on after about ten minutes at dead slow speed. (I turned on the heater, opened the cover, and steamed back to port at dead slow.)

Other than this, the engine runs fine. Also, be advised that this boat has had what would be considered minimum use, professional care, and never ran in "dirty" water (although the Ohio River is not "clean.")

Is it possible I need a new thermostat, or could this be something more ?

And BTW...I can't find anybody in the Cincinnati / Northern Kentucky area to work on my engine. Any referrals?

 

[SlackwaterJack]

Here's some ideas to look for, (I'm sure others will have more)
RAW WATER SIDE:
Is there enough water coming out of the exhaust? is it warm? hot?
Did you make sure the raw water intake was opened fully?
Have you checked the raw water filter? it could be plugged.
Hows the belt for the raw water pump?
Were the broken impeller blades ever found? they like to plug the heat exchanger.
If the new impeller wasn't lubed when it was installed or the engine was run without water in the raw water side it could easily have ruined the new impeller. If the impeller was installed with the vanes rotated to the wrong position that also could have caused some damage to the new impeller. It could even have had the wrong impeller installed.

ENGINE COOLANT SIDE:
Hows the engine's water pump belt? how old? too tight? too loose?
Have you checked the coolant level? enough/proper anti-freeze?
It's possible the thermostat is stuck closed or almost closed, so you may want to check that as well.

OTHER:
Is the engine actually hot or just the alarm sounding? ( you may want to buy or borow a temp gun to see if really IS hot) it could just be a bad temp sender.I'm not sure if the alarm sounds if a wire shorted or if a wire is cut/broken so you may want to trace the wires from the sender to the alarm. If you don't have a service manual (not just the owner's manual) get one. These engines are a breeze to do regular maintenance on (belts, fliud changes,impeller etc...).
These engines are also common to Yanmar yard tractors so you may have a Yanmar dealer with at least some diesel experience nearer than you think.
It's possible the guy that checked your cooling system doesn't fully understand how the cooling system works ie, did he flush the raw water system or the engine coolant side?

 

[RProffer]

According to the Yanmar website, this is the closest dealer in Ohio to you in Norwood:
http://www.mackboring.com/recreationalmarine/

You can check for others at the following link
http://www.yanmarmarine.com/index.cfm/go/Distributors/

 

[Andrew Custis]

Very good points made. Here is the steps I would take.

Raw Water System

1. Check impeller.
2. Check seacock to ensure it is not clogged and open. Have seen this many times as there is a pickup on the bottom with a filter. Weeds can get tangled in this not allowing the water to flow through the exhaust.
3. Check raw water hoses leading from seacock to filter, and filter to engine.
4. Check other side of engine from impeller to heat exchanger. As mentioned, blades can get sucked through if some were missing. (If an impeller has broken blades, its best to find all of the blades to ensure you do not clog the water flow going out through the exhaust)

Fresh Water System (Antifreeze)

1. Check cabin heater to ensure its getting warm when the engine heats up. This will usually indicate that the thermostat is operating correctly by opening and allowing the coolant flow through the closed cooling loop.
2. Check coolant levels. Always fill engine before filling the expansion tank.
3. Check to make sure coolant cap is tight. (Simple but have seen this be the problem)