"I would appreciate help in di
"I would appreciate help in diagnosing an overheating problem I have a 1986 Hallberg-Rassy 312 with a Volvo Penta 2003 Saildrive engine. About 2 years ago I had fresh-water cooling installed. Since then the engine has had about 70 hours of light use. Once last summer, after motoring at idle for at least an hour, I heard the over temperature alarm chatter briefly. Since then no problems.
A week ago we went on a river cruise which was mostly motoring. We had no problems for the first 20 hours. We got underway for the last leg and after about 4 hours the over temperature alarm came on. We anchored quickly and let the motor cool for an hour. Getting underway again the over temp alarm began sounding in only a few minutes. We sailed for several hours until we were near a good anchorage. In starting the motor to enter an inlet the alarm sounded within a minute. The next day we we towed to our dock.
To diagnose this problem I fastened thermocouples to the cylinder head (T1) and to the copper tube on the output of the heat exchanger that delivers raw water to the exhaust manifold (T2). I tied the boat to the dock so I could operate it in gear.
Here are the results, which I have also uploaded as a graph:
Time
Conditions and Results
1240
Started engine 1900RPM in gear; T1 rises to 76C and stabilizes, T2 rises to 28C when T1 crosses 74C.
1303
Turned on DC circuits with Alternator at 23A
1325
Dropped to 1000RPM still in gear; T2 drops maybe 2C
1331
Closed off engine comartment
1348
RPM back up to 2000RPM in gear, Alternator 20A; T2 rising steadily during next hour
1433
T1 at 85C, increased RPM to 2500 in gear; T1 climbs rapidly
1436
Over temperature alarm sound with T1 at 96C.
1436
RPM reduced 2000RPM in gear; T1 drops rapidly
1440
RPM reduced to 1000RPM and in neutral; Engine continues cooling
1445
Shutdown with T1 at 85C
There are some things I note:
1) The thermostat spec is for opening at 74C and fully open at 87C. The 74C opening is apparent on T2.
2) The engine oil is clean and at the full line.
3) The cooling system expansion tank is at the full line.
4) Twice during the operation at 2000RPM I collected exhaust water in a bucket, which measured the raw water flow at about 3.6 gal/minute.
5) There was no obvious slipping of the belts.
6) The water temperature in the harbor was 25C, and the raw water output of the heat exchanger was below 30C until the over heating began.
7) I might add that in the leg of the cruise in which overheating occured we had been living on house batteries for the preceding 2 days. I have a high output alternator which was probably charging at 50A while we were motoring at 2000RPM. So this might have driven us into the overload region.
I have uploaded a temperature graph of this test, and I would be very grateful for comments.
Thanks and kind regards, -- David
HR312 Engine Temp Test
"I would appreciate help in diagnosing an overheating problem I have a 1986 Hallberg-Rassy 312 with a Volvo Penta 2003 Saildrive engine. About 2 years ago I had fresh-water cooling installed. Since then the engine has had about 70 hours of light use. Once last summer, after motoring at idle for at least an hour, I heard the over temperature alarm chatter briefly. Since then no problems.
A week ago we went on a river cruise which was mostly motoring. We had no problems for the first 20 hours. We got underway for the last leg and after about 4 hours the over temperature alarm came on. We anchored quickly and let the motor cool for an hour. Getting underway again the over temp alarm began sounding in only a few minutes. We sailed for several hours until we were near a good anchorage. In starting the motor to enter an inlet the alarm sounded within a minute. The next day we we towed to our dock.
To diagnose this problem I fastened thermocouples to the cylinder head (T1) and to the copper tube on the output of the heat exchanger that delivers raw water to the exhaust manifold (T2). I tied the boat to the dock so I could operate it in gear.
Here are the results, which I have also uploaded as a graph:
Time
Conditions and Results
1240
Started engine 1900RPM in gear; T1 rises to 76C and stabilizes, T2 rises to 28C when T1 crosses 74C.
1303
Turned on DC circuits with Alternator at 23A
1325
Dropped to 1000RPM still in gear; T2 drops maybe 2C
1331
Closed off engine comartment
1348
RPM back up to 2000RPM in gear, Alternator 20A; T2 rising steadily during next hour
1433
T1 at 85C, increased RPM to 2500 in gear; T1 climbs rapidly
1436
Over temperature alarm sound with T1 at 96C.
1436
RPM reduced 2000RPM in gear; T1 drops rapidly
1440
RPM reduced to 1000RPM and in neutral; Engine continues cooling
1445
Shutdown with T1 at 85C
There are some things I note:
1) The thermostat spec is for opening at 74C and fully open at 87C. The 74C opening is apparent on T2.
2) The engine oil is clean and at the full line.
3) The cooling system expansion tank is at the full line.
4) Twice during the operation at 2000RPM I collected exhaust water in a bucket, which measured the raw water flow at about 3.6 gal/minute.
5) There was no obvious slipping of the belts.
6) The water temperature in the harbor was 25C, and the raw water output of the heat exchanger was below 30C until the over heating began.
7) I might add that in the leg of the cruise in which overheating occured we had been living on house batteries for the preceding 2 days. I have a high output alternator which was probably charging at 50A while we were motoring at 2000RPM. So this might have driven us into the overload region.
I have uploaded a temperature graph of this test, and I would be very grateful for comments.
Thanks and kind regards, -- David