I am still trying to solve an overheating problem (see "Hot Engine" post of 8/26/01) The engine heats very quickly and very hot under load. This is a Universal 25. I am satisfied that the raw water system is functioning as it should. I have taken the thermostat out and tested it. It opens properly. I now suggest that the flow of the fresh water is blocked or inadequate. If I feel the fresh water input and output hoses on the heat exchanger there is a definate difference in temp. but when I remove the radiator cap and look for signs of flow, I am not able to see anything that looks convincingly like the water is flowing through the system. I see movement in the coolant but this is more like a jiggeling then a flow which is probably just from vibration. Does anyone know how to test the fresh water pump and/or confirm that the coolant is actually flowing adequately through the fresh water system. Any help would be appreciated.
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Steve W.
quick check...
Bob, disconnect the heat exchanger discharge hose at the engine exhaust elbow and poke a phillips screwdiver in the elbow nipple to see if it is clogged. There is almost no way to clog the freshwater (antifreeze) side of your cooling system since there is no outside water (debris) being circulated thru it or impeller to break. So that leaves the freshwater pump and the thermostat. A broken freshwater pump shaft would be pretty obvious since the pulley would probably fly off. By process of elimination, that leaves the elbow nipple or some other clog upstream of the elbow nipple. Good luck.
Bob, disconnect the heat exchanger discharge hose at the engine exhaust elbow and poke a phillips screwdiver in the elbow nipple to see if it is clogged. There is almost no way to clog the freshwater (antifreeze) side of your cooling system since there is no outside water (debris) being circulated thru it or impeller to break. So that leaves the freshwater pump and the thermostat. A broken freshwater pump shaft would be pretty obvious since the pulley would probably fly off. By process of elimination, that leaves the elbow nipple or some other clog upstream of the elbow nipple. Good luck.
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Michael McCann
OVERHEATED!!!
Bob; I'm not sure if I understand rqw and fresh as you state. Raw water comes out the exhaust, fresh is circulated within the engine. Now, is there water coming out of the exhaust? Have you checked the raw water impeller? I would replace the impeller now. Have you checked the heat exchanger for a blockage to the raw water? Have you checked the screen of the raw water strainer where it enters at the through hull? I would suggest dissassembly of the raw water system and check it. You should be able to just remove the end caps of the heat exchanger and inspect the raw water passages. If you do not want to get this involved, check the raw water flow as Steve suggested. Now with the raw water system verified, lets look at the fresh water system. Remove the thermostat, get your wife's candy thermometer (don't let her know) place the thermostat in a pot of water and heat it until you see the thermostat open then take the temperature of the water in the pot. It should be about what the thermostat is set for. 165 degrees? Is this the incident where you overheated and lost all coolant? If so, when you replaced the coolant did you mix it 50/50 with water? Have you bled the fresh water system since adding this coolant? Check the temperature of the coolant in the expansion tank (the radiator cap) when the temperature is reading above the thermostat setting. You will only see movement in this tank if the thermostat is open, otherwise the coolant only flows to the hot water heater and back. If all these check out just try a new temp guage. Good luck. Mike
Bob; I'm not sure if I understand rqw and fresh as you state. Raw water comes out the exhaust, fresh is circulated within the engine. Now, is there water coming out of the exhaust? Have you checked the raw water impeller? I would replace the impeller now. Have you checked the heat exchanger for a blockage to the raw water? Have you checked the screen of the raw water strainer where it enters at the through hull? I would suggest dissassembly of the raw water system and check it. You should be able to just remove the end caps of the heat exchanger and inspect the raw water passages. If you do not want to get this involved, check the raw water flow as Steve suggested. Now with the raw water system verified, lets look at the fresh water system. Remove the thermostat, get your wife's candy thermometer (don't let her know) place the thermostat in a pot of water and heat it until you see the thermostat open then take the temperature of the water in the pot. It should be about what the thermostat is set for. 165 degrees? Is this the incident where you overheated and lost all coolant? If so, when you replaced the coolant did you mix it 50/50 with water? Have you bled the fresh water system since adding this coolant? Check the temperature of the coolant in the expansion tank (the radiator cap) when the temperature is reading above the thermostat setting. You will only see movement in this tank if the thermostat is open, otherwise the coolant only flows to the hot water heater and back. If all these check out just try a new temp guage. Good luck. Mike
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Chris Ward
Have you bleed the system?
Have you bleed the air out of the fresh water system? On my 1984 C-30 there is a petcock on top of the thermostat housing. Open to release trapped air with engine running. There maybe only a small amount of trapped air but it can cause the gauge to read hot. If there is trapped air, the temp guage will move very fast to 240 . This is because the sending unit in the thermostat housing is exposed to steam instead of water. The engine is not really running hot. Good Luck.
Have you bleed the air out of the fresh water system? On my 1984 C-30 there is a petcock on top of the thermostat housing. Open to release trapped air with engine running. There maybe only a small amount of trapped air but it can cause the gauge to read hot. If there is trapped air, the temp guage will move very fast to 240 . This is because the sending unit in the thermostat housing is exposed to steam instead of water. The engine is not really running hot. Good Luck.
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Bill B.
Air in lines???
I have a Catalina SR 30 with a Universal M-18 (14 HP), and I experienced overheating problems recently. I slowed the cruis engine speed down, and that helped only marginally. One evening I pulled the manuals down for study, and found that overheating was an entire section in the manual. What I found: 1) The coolant overflow tank was empty. 2) Through suction, air was sucked thru the check-valve into the cooling lines. The coolant lines were higher near the overflow tank, so the air was trapped in the upper end of those lines. The pump was not strong enough at normal speed to force the air from the lines. The manual said to rev the engine to up around 3000 RPMs a few imes to force the air back into the lower parts of the engine. This would allow the engine to begin it's Fresh water flow again. There was not much air, bu I topped the coolant off just the same after I finished. The water/engine temperature returned almost immediately back to the normal range. Hope this helps. Fair Winds... Bill B. s/v Eagle's Nest
I have a Catalina SR 30 with a Universal M-18 (14 HP), and I experienced overheating problems recently. I slowed the cruis engine speed down, and that helped only marginally. One evening I pulled the manuals down for study, and found that overheating was an entire section in the manual. What I found: 1) The coolant overflow tank was empty. 2) Through suction, air was sucked thru the check-valve into the cooling lines. The coolant lines were higher near the overflow tank, so the air was trapped in the upper end of those lines. The pump was not strong enough at normal speed to force the air from the lines. The manual said to rev the engine to up around 3000 RPMs a few imes to force the air back into the lower parts of the engine. This would allow the engine to begin it's Fresh water flow again. There was not much air, bu I topped the coolant off just the same after I finished. The water/engine temperature returned almost immediately back to the normal range. Hope this helps. Fair Winds... Bill B. s/v Eagle's Nest
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Tim Dranttel
Here is what my problem was
Bob, I had a similar problem. I could run all day at any RPM in neutral and temperatures would stay normal. As soon as I put the boat in gear any RPM over 1500 would result in overheating! I bled lines, replaced the thermostat and coolent cap with no luck. The raw water pump had a seal going bad so I replaced it and in the process decovered that although when I bought the boat I replaced the impeller, the previos owner had one come apart at some time and just replace the impeller without tracking down the pieces of the broke one. I found several peices blocking the elbow coming off the pump and more at the elbow going into the exchanger. Cleaned those out and my problem was a little better but not much! I had heard that the 25XP had a larger exchanger because the ones on the 25 were deemed too small. I ordered a 25XP exchanger from Defender and installed it. Now I can run any RPM, under any load, and even under full by-pass through the hot water heater and the Temp never gets above 170 degrees! My advice: 1-check for blockage at the pump output and the exchanger input elbows. 2-pull the end plate off of the exchanger and check for blockage there. 3-get the exchanger cleaned 4-get a new 25XP exchanger Tim
Bob, I had a similar problem. I could run all day at any RPM in neutral and temperatures would stay normal. As soon as I put the boat in gear any RPM over 1500 would result in overheating! I bled lines, replaced the thermostat and coolent cap with no luck. The raw water pump had a seal going bad so I replaced it and in the process decovered that although when I bought the boat I replaced the impeller, the previos owner had one come apart at some time and just replace the impeller without tracking down the pieces of the broke one. I found several peices blocking the elbow coming off the pump and more at the elbow going into the exchanger. Cleaned those out and my problem was a little better but not much! I had heard that the 25XP had a larger exchanger because the ones on the 25 were deemed too small. I ordered a 25XP exchanger from Defender and installed it. Now I can run any RPM, under any load, and even under full by-pass through the hot water heater and the Temp never gets above 170 degrees! My advice: 1-check for blockage at the pump output and the exchanger input elbows. 2-pull the end plate off of the exchanger and check for blockage there. 3-get the exchanger cleaned 4-get a new 25XP exchanger Tim
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