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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10898
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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The high water temperature alarm sounded on my VolvoPenta

Customer Question

The high water temperature alarm sounded on my VolvoPenta MD2030 engine. Opened engine compartment and steam billowed out with smell of antifreeze. Saw that the joint between fitting on top of the expansion tank that the pressure cap mounts on separated from the expansion tank. Added water to fill expansion tank, and was able to throttle down to lower RPM and engine functioned OK, at atmospheric pressure (no pressure cap) . A mechanic said the separated joint needed to be soldered, and that the entire expansion tank needs to be removed so the surfaces can be thoughly cleaned before soldering (at a radiator shop). Are there any special instructions for removing the expansion tank from the engine block , e.g. by removing the nuts from the studs, and detaching the various hoses. (assuming the joint can't be soldered with the expansion tank will attached to the engine.)? Seems to me new gaskets and new hoses are to be installed, as well as having the radiator shop test and clean the heat exchanger. Any advice or comments are welcome. (picture available)
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else important you think the Marine Mechanic should know?
Customer: I think I've covered it. Only other question would be, should I flush fresh or raw water cooling circuits in engine? If yes, with water or other fluid (e.g. phosphoric acid). Is it best to flush with the boat in or out of the water?
Submitted: 6 months ago.
Category: Boat
Expert:  Tan replied 6 months ago.

Hello, I'm Tan. Welcome to JustAnswer. I'm reviewing your question and will reply momentarily.

Expert:  Tan replied 6 months ago.

Are you referring to the neck of the fill cap where fill cap screws on?

Customer: replied 6 months ago.
the fact that the engine overheated in the first place means to me that engine heat wasn't being sufficiently transferred to the cooling raw water. Normally I'd expect that the overheated steam and fresh water coolant would have escaped by the cap venting when it's pressure limit was reached,instead of blowing out the weakest joint, so I'll be having the cap pressure tested and replaced if nor within spec.
Expert:  Tan replied 6 months ago.

This being a pressurized system it will over heat from loss of pressure and coolant. Now the heat exchanger will have to be removed for repair unless you can find a mechanic to do the job exchanger still on engine.

Disconnect all the hoses and remove the 6 bolts attaching the exchanger to the head.

Post back with questions.

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