07-28-2026, 07:28 AM
Trying to determine what would have caused the valve seat on cylinder #3 if my starboard engine to blow with no alarms, fault codes or warning.
I recently purchased a 2005 3600 Sovran with twin 6CTA8.3L-480CE turbo diesels. 970 hours on port engine, 1011 on the starboard. Survey was clean, 3 years of maintenance records suggested all was well cared for (no earlier records were available) and engines ran great on 5 hour trip home from Harbor Springs, MI to our home port of the Les Cheneaux Islands of Michigan's UP. Spent a few weeks rigging her out along with a few 1 hour cocktail cruises through the islands (usually running around 900rpm most of the time). Then set out for a 10 day trip into the North Channel of Lake Huron. Day 1: Ran approx 5-1/2 hours to our first stop (Gore Bay) keeping the engines at 2200rpm (73%) for most of that run. Dsy 2: Fueled-up and made a 2 hour run at 2000-2200 rpm to the Benjamin Islands where we dropped anchor for the night. Day 3: We headed out for a north coast cruise of the North Channel. We ran about 1-1/2 hours without issue and decided to stop at the small Blind River marina to top off the tanks. Engines ran smooth. Shut them down at the marina. Temperature gages were in normal range and no alarms or faults presented. Topped the tanks and started engines back up. Port engine started as smooth as butter. Starboard engine took a couple seconds to fire up and immediately gave out a rhythmic "steel-on-steel" CLING, CLING, CLING, CLING. Immediately shut down the engine and checked gages. Then tried restarting with same result.
Learned that the starboard engine controls the hydraulic steering steering, so with only a port engine the boat would only turn clockwise circles. Got a towed back to a good marina in the states and had a Cummins mechanic drive up to investigate. Within an hour, the engine dress was stripped off and we found (3) symptoms:
1. Cylinder #3 valve seat on cylinder head was fractured with debris lodged onto the piston
2. One of the two thermostats was broken in half
3. The small brass coolant check valve was broken.
Cummins suggests teplacing the following parts: cylinder head assembly, piston, piston sleeve, piston bearing, thermostas check valve, and completing a 1000 hr tune-up on both engines. (We checked North America and there are no Cummins head assemblies available. They are made to order with a 12 week lead time and 24 currently on back order. Boat is already pulled and in storage building awaiting parts. -Lost the season-
I'm currently concerned about going through this repair process only to have a similar issue on the port engine next year.
Questions:
1. Has anyone experienced this or similar on a Cummins 6CTA8.3L-480CE? (I expected 5000 hours before something like this)
2. I would tend to believe that excessive heat would be the root cause of a valve seat failure. And cylinder #3 is fairly close to the broken thermostat and check valve. Is it plausible these part failures created the valve seat failure?
3. Anyone with thermostat failure experience?
4. I did notice a considerable amount of heat coming from the engine room when I opened the hatch. Mechanic said the engine room should never be more than 30 degrees above ambient. I would guess it was at least 40 degrees delta. Did Tiara design-in enough air flow in the engine room on the 2005 3600 Sovran to handle these monster turbo diesels?
All insight appreciated.
I recently purchased a 2005 3600 Sovran with twin 6CTA8.3L-480CE turbo diesels. 970 hours on port engine, 1011 on the starboard. Survey was clean, 3 years of maintenance records suggested all was well cared for (no earlier records were available) and engines ran great on 5 hour trip home from Harbor Springs, MI to our home port of the Les Cheneaux Islands of Michigan's UP. Spent a few weeks rigging her out along with a few 1 hour cocktail cruises through the islands (usually running around 900rpm most of the time). Then set out for a 10 day trip into the North Channel of Lake Huron. Day 1: Ran approx 5-1/2 hours to our first stop (Gore Bay) keeping the engines at 2200rpm (73%) for most of that run. Dsy 2: Fueled-up and made a 2 hour run at 2000-2200 rpm to the Benjamin Islands where we dropped anchor for the night. Day 3: We headed out for a north coast cruise of the North Channel. We ran about 1-1/2 hours without issue and decided to stop at the small Blind River marina to top off the tanks. Engines ran smooth. Shut them down at the marina. Temperature gages were in normal range and no alarms or faults presented. Topped the tanks and started engines back up. Port engine started as smooth as butter. Starboard engine took a couple seconds to fire up and immediately gave out a rhythmic "steel-on-steel" CLING, CLING, CLING, CLING. Immediately shut down the engine and checked gages. Then tried restarting with same result.
Learned that the starboard engine controls the hydraulic steering steering, so with only a port engine the boat would only turn clockwise circles. Got a towed back to a good marina in the states and had a Cummins mechanic drive up to investigate. Within an hour, the engine dress was stripped off and we found (3) symptoms:
1. Cylinder #3 valve seat on cylinder head was fractured with debris lodged onto the piston
2. One of the two thermostats was broken in half
3. The small brass coolant check valve was broken.
Cummins suggests teplacing the following parts: cylinder head assembly, piston, piston sleeve, piston bearing, thermostas check valve, and completing a 1000 hr tune-up on both engines. (We checked North America and there are no Cummins head assemblies available. They are made to order with a 12 week lead time and 24 currently on back order. Boat is already pulled and in storage building awaiting parts. -Lost the season-
I'm currently concerned about going through this repair process only to have a similar issue on the port engine next year.
Questions:
1. Has anyone experienced this or similar on a Cummins 6CTA8.3L-480CE? (I expected 5000 hours before something like this)
2. I would tend to believe that excessive heat would be the root cause of a valve seat failure. And cylinder #3 is fairly close to the broken thermostat and check valve. Is it plausible these part failures created the valve seat failure?
3. Anyone with thermostat failure experience?
4. I did notice a considerable amount of heat coming from the engine room when I opened the hatch. Mechanic said the engine room should never be more than 30 degrees above ambient. I would guess it was at least 40 degrees delta. Did Tiara design-in enough air flow in the engine room on the 2005 3600 Sovran to handle these monster turbo diesels?
All insight appreciated.
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