Why is my Volvo Penta overheating?
I have a 2008 Volvo Penta D2-55 that has started running hot at cruising revs. The temperature alarm sounds if I push past 2000 RPM, but it cools down at idle. Water is coming out of the exhaust, but maybe less than usual. What should I check first?
Answer
Your Volvo Penta D2-55 is overheating at cruising revs because the raw water flow is restricted by a missing impeller vane, a blocked sea strainer or a scaled-up heat exchanger. The engine cools down at idle because it receives a small amount of water, just not enough volume to shed the heat generated under heavy load.
Check Impeller and Strainer
Always shut the seacock before opening the raw water circuit to prevent flooding the bilges.
The raw water strainer is your first stop. Inspect the clear plastic lid and pull the basket out. Eelgrass, plastic bags or jellyfish can partially block the intake and starve the engine at higher revs. If your boat has a saildrive, ensure barnacles are not fouling the intake slots on the leg.
Next, remove the raw water pump cover plate. Six 8mm bolts secure this plate on the front of the D2-55 engine. Extract the impeller using water pump pliers or a dedicated puller tool. Look for specific faults:
- Missing vanes: You must locate any torn rubber vanes. They usually wash downstream and wedge into the front of the heat exchanger tube stack. This blocks water flow entirely.
- Cover plate wear: Inspect the brass cover plate. Deep circular grooves cause the pump to lose suction. You can often flip the cover plate over to use the smooth outer face as a temporary fix.
- Cam wear: The brass cam shoe inside the pump wears down over time. This wear reduces pump volume.
Replace the impeller annually. A genuine Volvo Penta or Johnson replacement costs around £40.
Inspect Heat Exchanger Tube Stack
If the impeller is intact but flow remains poor, the heat exchanger is likely fouled. Calcium, salt scale and marine growth build up inside the cupronickel tubes over time. This drastically reduces cooling efficiency.
Drain the fresh coolant circuit to check the matrix. Do not open the pressure cap when the engine is hot to avoid scalding. Remove the rubber end caps from the heat exchanger. Pick out any broken impeller vanes with long nose pliers. If the tubes contain hard white scale, rod them gently with a brazing rod or a .22 rifle cleaning brush to clear the worst deposits. For heavy scale, circulate a marine descaler like Rydlyme or Barnacle Buster through the raw water circuit. Use a cheap bilge pump in a bucket and run it for two hours.