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Old 05-13-2004
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Volvo MD11C Overheating

I have a Volvo MD11c that is raw water cooled and is overheating. Last season the temp would climb until it hit the red zone then move back well into the green zone(cooler). I have replaced the pump thermostat. A large volume of water exits the exhaust.
This season the temp climbs up to just near the red zone and stays there.
I think I need to remove the exhaust manifold and boil it out.
Am I on the right track? Also any advise on how best to remove it, any tricks and should I try to clean the water jacket on the block?
BTW: the boat is a Pearson 323
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Old 05-13-2004
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Volvo MD11C Overheating

Whats the volumetric cooling water flow rate at X rpm? Dont have a manual or the data - call your distributor for the info.

Go to your manual and obtain the data, then run the engine at the spec. rpm until the thermostat fully opens, take a bucket and stop watch and catch the water coming from the exhaust. If the output is not up to spec. then you have a blockage somewhere: broken impeller vane jammed downstream in a hose, fouled thermostat, exhaust manifold starting to form ''platelette'' rust in the cooiing passages. Cast iron exhaust headers will form huge rust plateletts which break off from the interal cooling passage walls and block or partly block the flow - especially happens if you drain the water from engine during layup and let the cooling system "dry-out". If so, just poke a large stiff wire into the header to break up the flakes.... then check for pin holes into the ''gas side''.
You dont state if this is a fresh water (exhcanger) system or a raw water cooled engine. If the volumetric flow is within spec. then consder to ''pickle'' the engine to remove carbonate ''boiler'' scale by using an organic descaling agent such as Marsolve or RydLyme. If you use acid, you can dissolve the base metal of the engine as well as the scale.

When was the last time you changed the pump impeller(s)? Should be yearly!

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Old 05-16-2004
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Volvo MD11C Overheating

I have the same engine, but it was converted to fresh water cooling several years ago. Still, last summer it was overheating, but I could run it at about 1000 rpm for some time. To make a long story shorter, one of the (three) internal ports between the exhaust manifold and the block was clogged. So a thorough break-down and cleaning seems in order for you.
Good luck.
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