Engine overheating problems

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Men a vaur

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Hi Everyone

I’m continuing to have overheating issues with my MD2020 engine. I’ve replaced the temp sensor and the thermostat for starters but have not solved the issue. The symptoms are as follows:

- Engine overheating alarm sounds when engine is in forward or reverse after a few minutes.
- Heat exchanger doesn’t appear to be overheating
- Calorifier is not heating domestic hot water
- Domestic water tank is draining within 24 hours of filling up with all taps closed (seems to be overboard as there’s not much water in the bilge)
- Plenty of raw water coming out of exhaust and not excessively hot (eg no steam) making me think it is the freshwater system that is causing the issue.

Things I’ve done to try and resolve so far:

- New thermostat and temp sensor
- Heat exchanger has been removed and cleaned - all debris removed
- New hoses fitted to fresh water system and spigots cleaned
- New raw water impeller fitted and gasket replaced

I’m a bit unsure as to how the domestic water tank is draining 70 litres in less than 24 hours but suspect this is all connected to my overheating problem and am wondering if I have cracked pipes/ a leak in my calorifier between the domestic water system and the engine coolant/freshwater loop. However, I don’t understand how this would cause the overheating problem. Has anyone experienced anything similar or have any suggestion/advice on how to resolve this?

thanks very much
 
  1. You might have a blockage in the raw water exhaust elbow just after the heat exchanger (quite common problem)
  2. I assume you have checked the raw water incoming pipework for any blockage from the raw water sea cock to filter to the impeller
 
Thanks for the pointers.. I’ve checked the raw water in and all is good there. Have not checked the exhaust elbow yet so will take a look at that. Would a blockage in the exhaust elbow not lead to no water coming out of the exhaust or does it just reduce the flow?
 
I assume loss of your fresh water is with the engine running? As mattonthesea alludes, if there is a leak in the calorifier heating coil, domestic water pump pressure is higher than seawater cooling pressure, which will cause the fresh water to leave by the exhaust. I think the same thing would happen if there was a leak in the heat exchanger. The difference is that when the engine is stopped and the domestic pump is on, the bilge will fill with coolant if the leak is in the calorifier.
 
vyv_cox said:
I assume loss of your fresh water is with the engine running? As mattonthesea alludes, if there is a leak in the calorifier heating coil, domestic water pump pressure is higher than seawater cooling pressure, which will cause the fresh water to leave by the exhaust. I think the same thing would happen if there was a leak in the heat exchanger. The difference is that when the engine is stopped and the domestic pump is on, the bilge will fill with coolant if the leak is in the calorifier.
Click to expand...
I am confusing myself here! With indirect cooling the domestic water will go to the bilge with a calorifier leak. Heat exchanger leak sounds more likely.
 
Men a vaur said:
Hi Everyone

I’m continuing to have overheating issues with my MD2020 engine. I’ve replaced the temp sensor and the thermostat for starters but have not solved the issue. The symptoms are as follows:

- Engine overheating alarm sounds when engine is in forward or reverse after a few minutes.
- Heat exchanger doesn’t appear to be overheating
- Calorifier is not heating domestic hot water
- Domestic water tank is draining within 24 hours of filling up with all taps closed (seems to be overboard as there’s not much water in the bilge)
- Plenty of raw water coming out of exhaust and not excessively hot (eg no steam) making me think it is the freshwater system that is causing the issue.

Things I’ve done to try and resolve so far:

- New thermostat and temp sensor
- Heat exchanger has been removed and cleaned - all debris removed
- New hoses fitted to fresh water system and spigots cleaned
- New raw water impeller fitted and gasket replaced

I’m a bit unsure as to how the domestic water tank is draining 70 litres in less than 24 hours but suspect this is all connected to my overheating problem and am wondering if I have cracked pipes/ a leak in my calorifier between the domestic water system and the engine coolant/freshwater loop. However, I don’t understand how this would cause the overheating problem. Has anyone experienced anything similar or have any suggestion/advice on how to resolve this?

thanks very much
Click to expand...
Following on from what gordmac said, if the alarm is sensing coolant temperature, then a couple of minutes is an unusually short time to get the block to more than normal running temp. Do you have more than one sensor? My Vetus engine has a coolant sensor and an exhaust injection sensor both linked to the same alarm. After the alarm sounds, carefully remove pressure cap and stick a thermometer in.

www.solocoastalsailing.co.uk
 
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I would suggest you isolate the calorifier first. Remove both pipes to the calorifier and temporarily seal both connections on the block. Run the engine and see what happens: does the alarm goes off irrespective it is in forward, reverse or neutral. If it ony sounds in forward or reverse, I would suspect the alarm unit on the instrument panel. Does the heat exchanger get very hot, does raw water exit.

With the calorifier isolated and the coolant circuit sealed but still full of water both domestic and the coolant side, do you lose domestic water? If so there is a leak elsewhere than the coolant elsewhere. If you don't lose domestic water, now unseal the coolant circuit with both ends higher that the domestic water tank. Now pressurise the domestic water. If water comes out of the coolant circuit, there is a leak in the coil somewhere inside the calorifier.

The colorifier not heating the water is typical of an air lock. But of course an air lock wouldn't affect the loss of the domestic water.

Except all that, dare I ask if someone has properly connected the 2 pairs of pipes into the calorifer? If the domestic water into the calorifier had been wrongly connected to on side of the coolant circuit, the domestic water would go out through the heat exchanger and exhaust nicel aided by the pressurised doemestic water. Bizarre point but......
 
Men a vaur said:
Thanks for the pointers.. I’ve checked the raw water in and all is good there. Have not checked the exhaust elbow yet so will take a look at that. Would a blockage in the exhaust elbow not lead to no water coming out of the exhaust or does it just reduce the flow?
Click to expand...
A blocked cooling water exhaust elbow will reduce the cooling discharge flow to the point of almost blocking it in time, needs removing and cleaning inside at least its another possibility off you list, good luck
 
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