I have a 1988 Hunter 28.5 with a Yanmar 2GM20F engine. Incidentally, I'm in Minnesota, there is still a very hard crust on Lake Pepin!
Last September, the temp alarm went off as I was motoring in, so I shut down immediately (we were just cruising into the dock). After a short troubleshooting stint, I found the anti-freeze was low. I kept it full for the remainder of the season until pull out. I also took an automotive coolant pressure tester and found that the system would not hold pressure. I also checked the coolant input for any air bubbles (indicating a leak in the head gasket), no bubbles. I could not detect any external leaks, so I figured that it could well be in the heat exchanger round rubber gaskets into the cooling water. There is no anti-freeze in the oil. I changed the oil/filter last fall.
Fast forward to last week where I removed the board that covers the back side of the engine, to gain better access to the back of the engine (I still want to check the engine exhaust mixer). I removed the heat exchanger (pretty straight forward) and found that the round gaskets on each end of the exchanger were in very good condition. There may have been some small leaks on the other end gaskets (fresh water input/output) but this would only let fresh water bypass the coolant tubes, but would NOT leak to the coolant side!
Surprisingly, the tube in the heat exchanger are all very shiny on the inside where the fresh water flows through! There's some grit and grim on the coolant side of the tubes, but looking down the tubes there is no corroded tubes that I can detect.
I'm not sure where to go next.
I may try to do an initial cleaning of the exchanger and see if I can figure out a way to seal both ends and somehow use a balloon to see if there is a leak anywhere on the exchanger. I can do this here at home.
Similarly, I might try to re-install the exchanger end pieces (input and output) on the engine without the exchanger installed and seal up the hose inputs (single hose from input to output) and try to pressurize the coolant system from the coolant input (remove the cap).
I thought about the water heater, but there is no anti-freeze in the water heater (it's currently bypassed), and I'll probably remove it anyway. We don't really use it.
The trouble is, I can't think of anywhere else that there could be a leak, other than the head gasket and thermostat (I did purchase a new thermostat that I'll put in before the end of the job.
Would I dare use a coolant system leak sealer? I've used it successfully in the past on cars (long term). Seems like it would be worth a try as a last resort rather than having to remove the head!
Any other ideas on where to find the leak, or where else it could be?
Mike
Last September, the temp alarm went off as I was motoring in, so I shut down immediately (we were just cruising into the dock). After a short troubleshooting stint, I found the anti-freeze was low. I kept it full for the remainder of the season until pull out. I also took an automotive coolant pressure tester and found that the system would not hold pressure. I also checked the coolant input for any air bubbles (indicating a leak in the head gasket), no bubbles. I could not detect any external leaks, so I figured that it could well be in the heat exchanger round rubber gaskets into the cooling water. There is no anti-freeze in the oil. I changed the oil/filter last fall.
Fast forward to last week where I removed the board that covers the back side of the engine, to gain better access to the back of the engine (I still want to check the engine exhaust mixer). I removed the heat exchanger (pretty straight forward) and found that the round gaskets on each end of the exchanger were in very good condition. There may have been some small leaks on the other end gaskets (fresh water input/output) but this would only let fresh water bypass the coolant tubes, but would NOT leak to the coolant side!
Surprisingly, the tube in the heat exchanger are all very shiny on the inside where the fresh water flows through! There's some grit and grim on the coolant side of the tubes, but looking down the tubes there is no corroded tubes that I can detect.
I'm not sure where to go next.
I may try to do an initial cleaning of the exchanger and see if I can figure out a way to seal both ends and somehow use a balloon to see if there is a leak anywhere on the exchanger. I can do this here at home.
Similarly, I might try to re-install the exchanger end pieces (input and output) on the engine without the exchanger installed and seal up the hose inputs (single hose from input to output) and try to pressurize the coolant system from the coolant input (remove the cap).
I thought about the water heater, but there is no anti-freeze in the water heater (it's currently bypassed), and I'll probably remove it anyway. We don't really use it.
The trouble is, I can't think of anywhere else that there could be a leak, other than the head gasket and thermostat (I did purchase a new thermostat that I'll put in before the end of the job.
Would I dare use a coolant system leak sealer? I've used it successfully in the past on cars (long term). Seems like it would be worth a try as a last resort rather than having to remove the head!
Any other ideas on where to find the leak, or where else it could be?
Mike
