What do I check next?

[Retirement Dream]

I have a 2014 R27 with a D3-200 Volvo Penta diesel engine. At operating RPM of less than 3000, the motor runs between 178 and 182 degrees F depending on the day.

However, within 5 to 10 minutes of hitting 3000 RPM or above, the engine temperature rapidly rises to above 190 degrees F and the RPM drops down into its “protected, safe, mode” of about 800 at which point the temperature rapidly falls down to around 180 F again and I once more have the ability to increase RPM to anything below 3000.

I have already cleaned and/or replaced all of the filters; replaced most of the hoses involved in the cooling system, made sure I had plenty of new oil in the engine; and, replaced the antifreeze.

What should I check next?

Scott on Retirement Dream
Santa Cruz, CA

 

[misinger]

The impeller. When I had the impeller changed during a 400 hour service my temperature at 3000 rpm dropped 10 degrees.


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[BB marine]

*Sea strainer check
*Thru hull pick up clean with no growth obstructing water flow
*Reverse gear cooler clean with no debris in it obstructing flow
*Impeller inspection and replacement

* If after performing previous inspections there is no change. A chemical flushing of the raw water cooling may help. This will remove marine growth and salt deposits if present to allow better raw water flow thru the after cooler (cooling induction air) and better raw water flow though the heat exchanger to be more efficient at removing heat form the coolant fluid.

* A thermostat that is either stuck partially open or failing to open all the way. The thermostat begins to open approximately 178F it opens full at approximately 200 F you should get a warning light or indicator around 200 F and the engine should derate around 209F. A thermostat operating improperly will cause an over heat.

The R27 200hp Volvo has a 1" thru hull water pick up. The designed and recommended water pick up for that engine is 1 1/4". With a smaller pick up the cooling flow is reduced about 20%. With the 20% reduction in flow the engine can function as per manufactures specifications. So a clean system, hoses, exchangers, a new or low hour water pump impeller and housing with little wear that is functioning at 80% efficiency or higher. The cooling system can operate efficiently.The installed cooling system works!

Now add a 20% blockage (normally a system if installed to manufactures specification can operate at this amount of restriction) and still maintain proper cooling for the engine. Operate with a pump with 20% or more reduced capacity because of wear do to hours or abraision. Then add the reduction in efficiency do to the reduced intake diameter (1" instead of Volvo's recommended 1' 1/4) and the result is an overheat. You may have a combination of a slight build up of deposits in the exchangers, a weak water pump combined, some fouling in the water intake with the already built in 20% reduction of flow (1" though hull ) = and over heat. The installed system works, it is marginal and requires a clean system and a good water pump to keep the engine running with-in specifications. Some Tug and Cut owners have changed the intake size to 1 1/4 and found a cooler running system others have maintained the 1" by increasing the frequency of impeller changes and flushing the raw water system to help maintain proper cooling and seem to be successful at maintaining the engine temperatures below the overheat threshold .

One other issue that can add to a engine operating at higher temps is a fouled bottom. What is your WOT RPM can you turn above 3900 rpm? If you have a fouled bottom plus a slightly restricted raw water cooling system you may see elevated temperatures from that also. Good luck with you troubleshooting!

 

[Red Raven]

Check for debris in the raw water intake under the boat. I picked up a wad of eel grass this summer and had very similar symptoms. Tried back flushing from inside but eventually when for a snorkel swim and found the problem. The other place that easily gets obstructed is the input side of the reverse gear cooler. Backflushing the cooler usually results in some stuff coming out.

If those two prove AOK then do the impeller.

Curt

 

[Retirement Dream]

Thank you for all the good advice. It turned out to be the impeller.