10M 454 closed system overheating
Posted: Mon Jul 09, 2018 7:55 pm
I have a 1982 10m, with 454 350hp closed cooling that is overheating and melting exhaust hoses. I am at a loss as I have done just about everything except replace manifolds and circulating pump. The impeller was new and checked good flow. There is no coolant/ water leak outside the motor and no chocolate milk inside the motor. I have checked all basics and in between many times... raw water pump fins, tranny cooler, pickup tube. Here is what I have done so far....
Last year I overheated, found out no antifreeze in tank. Filled it up with new antifreeze and took trips to downtown for dinner 15 mins each way. After trips checked the level in heat exchanger and it was a little low. I swapped heat exchanger side to side to see if problem followed it did not. I opened the end caps of the exchangers and backflushed and check tubes for build up. Nothing was there and looked good. Put it back together and still losing antifreeze. Pressure tested heat exchanger on motor with radiator pressure tester, it held good pressure. But sill losing fluid. Pulled off the heat exchanger off as I had a yearly vacation and pressed for time and plumbed it as an open system without splitting the risers as I wanted to go back to the original system. It ran a little hot at 200 removed thermostat runs 180. Was still running hot so took the block down to short block thinking it could be a head gasket. Really had my doubts along with our friends but running out of ideas... head gaskets were good, but found flatten cam shaft during process so replaced. Out of time and gambled made the trip fine 1.5 hours each way, ran 180 all day long. Finished the rest of the year like that with no problems but still wanted the closed cooling back on the boat.
Fast forward to 4 weeks ago same set up still on the Boat and take a weekend trip 2 hours each way. Boat ran good no problems on the way there. On the way back it ran great no problem but more steam from that side, temp was good. Checked after trip and exhaust hoses were melted from riser to 90 fitting and to the T fitting other the other bank. But good after the T fitting. Melted so bad is ran out the ends of the hoses. After removal it burnt through the inside layers.
I ran motor with the exhaust hoses off to check flow it has good water coming out. I took the heat exchanger to radiator shop it test good, did multiple test no problems. Remount everything back to stock with heat exchanger and no thermostat and new exhaust hoses and filled with water. Headed downtown for fireworks at cruising speed 2800. 5 minutes into the trip someone smells rubber and temp is climbing fast to 150. Opened the hatch and water peeing out the overflow. Turned off and idled there and back.
I am going to do the circulating pump in the next day. My thought is maybe the fins corroded away from the inside. It’s 35 years old I know it’s a slim shot but it’s $40 and cheaper than exhaust and motor.
Please let me know if you have had this problem ideas thoughts anything. Thank you. David
Last year I overheated, found out no antifreeze in tank. Filled it up with new antifreeze and took trips to downtown for dinner 15 mins each way. After trips checked the level in heat exchanger and it was a little low. I swapped heat exchanger side to side to see if problem followed it did not. I opened the end caps of the exchangers and backflushed and check tubes for build up. Nothing was there and looked good. Put it back together and still losing antifreeze. Pressure tested heat exchanger on motor with radiator pressure tester, it held good pressure. But sill losing fluid. Pulled off the heat exchanger off as I had a yearly vacation and pressed for time and plumbed it as an open system without splitting the risers as I wanted to go back to the original system. It ran a little hot at 200 removed thermostat runs 180. Was still running hot so took the block down to short block thinking it could be a head gasket. Really had my doubts along with our friends but running out of ideas... head gaskets were good, but found flatten cam shaft during process so replaced. Out of time and gambled made the trip fine 1.5 hours each way, ran 180 all day long. Finished the rest of the year like that with no problems but still wanted the closed cooling back on the boat.
Fast forward to 4 weeks ago same set up still on the Boat and take a weekend trip 2 hours each way. Boat ran good no problems on the way there. On the way back it ran great no problem but more steam from that side, temp was good. Checked after trip and exhaust hoses were melted from riser to 90 fitting and to the T fitting other the other bank. But good after the T fitting. Melted so bad is ran out the ends of the hoses. After removal it burnt through the inside layers.
I ran motor with the exhaust hoses off to check flow it has good water coming out. I took the heat exchanger to radiator shop it test good, did multiple test no problems. Remount everything back to stock with heat exchanger and no thermostat and new exhaust hoses and filled with water. Headed downtown for fireworks at cruising speed 2800. 5 minutes into the trip someone smells rubber and temp is climbing fast to 150. Opened the hatch and water peeing out the overflow. Turned off and idled there and back.
I am going to do the circulating pump in the next day. My thought is maybe the fins corroded away from the inside. It’s 35 years old I know it’s a slim shot but it’s $40 and cheaper than exhaust and motor.
Please let me know if you have had this problem ideas thoughts anything. Thank you. David