Volvo D6 Overheating

[Tim Porter]

Have a 2014 C30 sedan with Volvo D6 370 hp engine. Regularly serviced, just replaced raw water impeller last year.Never any problems. About 400 hours on engine. After launch took it out for seasons first trip this weekend. Engine has always run spot on at 185 deg temp. Idling through no wake zone no problem for about 25 minutes. As soon as started to increase revs temperature climbed right up .went to 240 deg. Temp alarm came on. I idled back to dock with temp hovering around 245 deg had Tow Boat US follow just in case. Boat in Merrimac River in MA and current is tough. Seacock open, strainer clean and getting plenty of water. Problem seems to be downstream. Thinking thermostat? Noticed no hot water in fresh water system. Water is heated when engine running. Always have hot water after running. Not sure what else it could be unless new impeller went bad. Long winded explanation but looking for feedback.thanks in advance!
Tim

 

[ridesn]

Not sure what else it could be unless new impeller went bad.

Are you seeing raw water leaving the exhaust port as expected?

 

[bob daily]

Mr. Tim, Troubleshooting your problem would be best accomplished by understanding the coolant system which is made up of two separate systems, Raw Water (sea water) and Fresh Water (antifreeze).
Raw Water system consists of hull valve, water strainer, raw water pump, heat exchanger , wet exhaust and exhaust port. If water is exiting the exhaust port when engine is running that side of the coolant system is working.
Fresh Water (antifreeze) system is the same design as your automobile with the thermostat and a water pump for circulating the antifreeze. Basic but hope this helps your troubleshooting.
Bob

 

[Cutwater28GG]

beyond a regular coolant issue, Ive seen 2 typical causes here on tugnuts that are worth a search for.

heat exchanger plugged/corroded.
turbo coked up from lots of low RPM use.

 

[Bobby P.]

You could have barnacle and other build up in your system. I started running hot and did all standard checks. I ran barnacle buster through the system and cleaned out a bunch of growth/deposits. Following this, engine temp went back to consistent 185 degrees. I made the use of BB part of my regular maintenance.
The “how to” of BB is well published online. I prefer to use a bucket and circulating pump.

 

[BB marine]

The one point you made about no hot water from the hot water tank makes me think Thermostat. There are 4 reasons why the Bus heater and hot water tank do not get hot. (1) the ball valves are closed so the antifreeze doe not circulate through them. (2) the engine circulator pump is damaged or belt is slipping which would also indicate the seawater pump is slipping.(3) Thermostat is stuck in a closed position. All of these conditions would reduce flow of hot anti freeze to the exchangers of these components.(4) the anti-freeze level was low and there was not enough coolant in the system. You know the engine temperature was elevated by the alarm. Did you do a hand check on the exchanger for temperature increase ? Higher than normal? Did you have overflow from the expansion tank? What other signs of an overheat did you experience?

I would replace the impeller, check belt tension, check anti-freeze level, check ball valves (open), check the engine running temperature with a pyrometer or temp gun. Check the exhaust elbow discharge temperature proving it is cooled from sufficient water flow. If you find all these checks or replacements did not point you to the issue and prove the issue is not raw water side or simple fresh water side issue. I would replace the antifreeze flush the coolant system, replace the thermostat and fill with new antifreeze, confirm all air is removed from the system than retest.

My gut feeling is thermostat but that is a guess from 1200 miles away!!

 

[Tim Porter]

Thanks for the feedback, turns out it was fairly simple. Everything checked out. The best guess is the intake strainer on hull was plugged. Sea trialed and after hitting cruising rpm temp was rock solid at 185 deg F. Go figure. A lot of “stuff” in Merrimac RiVer.