Engine overheating! I need answers

Went for a sail last night and when I was motoring back into the harbor, my engine started to overheat. Smoke was coming out of the engine compartment. Luckily I had a good enough wind to shut it off and sail back onto the mooring. Im new to boat engines but when I took a look it seemed like there was damage to the exhaust elbow. When the engine was running, there was plenty of water spitting out of the back of the boat, but the elbow joint on what Im guessing is the mixing component was so rusted it broke off in my hand. Anybody know what Im talking about or what its called, or where I can find a replacement part? Cost? Difficulty of installation? Anything would be helpful....

Overheating can be caused by a couple of things. If you are pumping water most likely the cooling jacket and elbow are corroded through. I had to replace mine last year. While it is apart check the heat exchanger cooling jacket that is connected to the mixing elbow. The jacket tends to corrode through right before where it enters the elbow. If you are loosing coolant the cooling jacket is definitely corroded through as well. Other than parts which cost about 1K for the elbow jacket and seals the replacement is not that bad. If you add coolant and the jacket is leaking it tends to run down into the engine, then the engine hydraulic locks and you have to get the coolant out before it will crank. If you need PM me and send a number and I can talk you through the replacement.

Chuck

Ive been trying to do some research and Im thinking the heat exchanger is not the problem. Im not sure what this piece is called, but hoping one of you might. Its a Volvo Penta MD7A engine, not a Yanmar. The piece that broke I believe is part of the exhaust system, because when I turn on the engine (I ran it just for a minute to see if I could identify the problem), exhaust and a small amount of water come out of the piece that broke off. From that piece, there is a hose that runs to what I believe is the bottom of the heat exchanger. I took some pictures of the part where the piece broke off, and a picture of where that hose runs. This part is oval and cylindrical and bolts to the engine right above where the propeller shaft comes out of the engine.

Sorry for the small pics, here are better ones.

Does a water-cooled exhaust bend sound right? I havent been able to find one that looks like mine, but I have been searching nonstop and this seems like its the closest thing to mine. Could a crack in this cause the engine to overheat?

Hi CapeDiver 714

we had a similar problem with our original 4 series Yanmar 50 in our 1998 IP40 - on the 'Admiral's' first trip.... being part 2 of the delivery on Australia's eastern seaboard.

Transpires that there was corrosion in the aft end of the exhaust manifold housing (the box that houses the heat exchanger). The Brisbane based Yanmar specialist mechanics hypothesised that it was from a drink coming through the transom and up the exhaust. I dunno about other IPs, but on the 40's it's one hell of a big roller coaster loop to get up and over.

Anyway, there was an old elbow amongst all the gear, which the previous owners (owned her since 2007) got with the boat.

Anyway, the housing (but not the heat exchanger) needed replacing.

The cost of the part was about $1900 AUstralian Dollars, from Japan .... near enough to the same in US Dollars.

However it all seems good for now - finger's crossed.

(And yes, she was pumping water and all that - just the temperature was going from zero to off the dial after about 3 minutes running).

I'd be interested to hear what others thing - I attribute it to age.