Re: Onan shuts down under load without shutdown codes


The operating temperature (oil) should be about 80C and the exhaust elbow about 50C.

The issue is that you are not getting enough saltwater through the heat exchanger.

The causes are multiple, but could be one of these more common causes:
  1. The supply of saltwater to the Onan may be restricted. Check the sea chest strainer and the primary saltwater manifold (photo below) connected to the sea chest. You may need to check hoses from the sea chest to the Onan raw water pump.
  2. The impeller blades are worn, broken, cracked, or set in place causing the lack of flow. Your Onan needs OEM impellers that are changed every 250 hours or 1 year, whichever comes first. Just because you see water exhausting the boat, doesn't mean it is enough water and it does not mean the impeller is good. I cannot tell how much water is enough by looking at the exhaust.
  3. Impeller blades may be logged inside the Onan raw water pump. Remove the pump and inspect for blades.
  4. The impeller is held in place by a key. The key will wear and sometimes cause the shaft to spin inside the impeller. This is hard to recognize.
  5. The heat exchanger and/or hoses connected are partially clogged with broken blades and/or debris. Remove the heat exchange and have it professionally cleaned. Take this opportunity to repaint it and install a new anode. Purchase 2 end cap kits part number 130-5176. These end caps are fragile and may break when they are removed (photo below).
  6. The following is something that you should either do every 2-3 years: The exhaust manifold and/or exhaust elbow might be partially clogged with carbon. Remove the exhaust elbow and inspect it. You will probably be able to see inside the exhaust manifold. If carbon buildup is present in either, clean them.
Onan exhaust elbow and exhaust manifold in red circles. Required gaskets in the green circles:

CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
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On Sat, May 1, 2021 at 6:54 AM Slavko Despotovic <slavko@...> wrote:

Hi Bill,

I have a problem with generator overheating (106 dC) coolant temperature . Sea water exhaust temperature up to 80 dC. Have checked impeller (it is new) , new oil, fuel filters, new oil. Before service at 1000 hours it was working ok. I am thinking that thermostat might be a problem. Or should I concentrate on seawater cooling system?
question is if thermostat fails( it is open, no flow od coolant) is the seawater system strong enough to cool the engine on 80 dC? In my generator this is not the case.

thank you.


SM 2000
#279 Bonne Anse in Portoroz

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