[johnhesch]

This scenario evolved over the past year ...

My Volvo D6-310hp port engine was overheating (205F) at full throttle (3600 rpm) for 2-3 minutes.  Rolling back to 3200 rpm brought back temp to normal (185F).  

I immediately thought of an obstruction in raw water, or possibly Impeller.  As I was coming back in, I noticed the coolant temp actually overshot cooling to about 165F but recovered (now coolant thermostat on my mind)

So back safely at dock, I went to work ..

1) strainer clean
2) Impeller pulled ... no noticeable wear (only had 15 hours on it).  It was replaced with new one.
3) Coolant drained and tstat pulled.  Coolant tested to protect to 245F.  Tstat tested on stovetop, with water and digital thermometer.  It opened fully at about 210 so I suspected that was the issue.  Used the Tiara supplied spare in the spares kit.  Replaced coolant with new.  Time for a test run.

Monitored both oil temp and coolant temp.  I noticed oil temp crept up faster on port than starboard.  Coolant seemed to be better regulated but still exhibited overtemp at full throttle.  Back to dock.

Research on net showed possible oil tstat issue (tstats on my mind).  So replaced it during oil change.  Oil cooler had some crud in it but nothing at all bad.  Cleaned it up without too much disassembling.  Couldn't test run due to cold weather here in Ohio, but no leaks on firing it up.  It took a long winter nap after.

Fast forward ... test run this spring showed problem still existed.  Finally got the time to tear into it to do a barnacle buster wash.  Pulling out anodes, of course one got stuck in the intercooler.  So had to take off the end plate... and now I truly believe I found the culprit.  See pic.

Obviously this happened over the 13 years/800 hours of its life in freshwater (only owned by me for last 2 years). Never pulled apart, not even winterized (heated storage its whole life) as the drain plugs all still had factory paint on them. My feeling is the raw water evaporates over winter and leaves a bunch of crud/calcium behind like an old water heater bottom.

New anodes on the way. I'll clean up the scars on the brass, one oring ripped taking apart ($52!). Should be fixed, cleaned, and back together this weekend. Will replace some suspect hoses at end of season too.

Starboard engine looked just as bad but doesn't overheat ... yet. Gotta love Swedish iron!

So keep your heat exchangers clean everyone! Volvo D6 has 5 (fuel, intercooler, oil, coolant, and transmission)per engine!!!

[trit21]

My boat live in salt water in FL and I do mine every 2 years. Maintenance maintenance. I have Cummins 6bta-370. I removed my fuel cooler as they are a weak point in the system and just not needed.