Engine Overheating?

[DKnight]

My boat is a Moody 336 with a raw water cooled Volvo 2003, When motoring the engine over heat alarm occasionally goes off, and there is no water coming out of the exhaust. So I switch the engine off, check the oil, impeller, and stainer and they are all O.K.This happened three times last season, but has happened twice already this season.
So I sail or drift for 15-20 minutes, re start the engine, the cooling water starts coming through again, so off we go. It does not seem to be dependant on how long or how hard the engine has been worked.
So I believe that the intake on the bottom of the hull is possibly getting blocked by weed or rubbish, the suction of the water trapping this blockage, until it washed free by switching the engine off, and sailing. The intake being just a plain hole without a cage.
Have any of you guys experianced anything similar or heard of anything like this? What rectified the problem? Or am I looking in the wrong area?

<hr width=100% size=1>DK

 

[dickh]

Has the impellor vanes become unbonded from the central boss? Not sure about Volvo impellors but there was a problem with Yanmar impellors - looks OK until you remove them and give the rubber a good twist etc to see if it is still bonded to the boss.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[brianhumber]

You could be right, but weed never selfclears from my inlet cock without me pushing it out.
Other generic items to check
Impeller not slipping on shaft
shaft not driving through coupling device
shaft sheared internally so only drives on the friction between the two broken bits ( this had me foxed for over a day once)
bit of internal hose broken off and moving around blocking flow
bits of hose/weed/scale moving around in heat exchanger blocking flow.
Work around your system checking items off one by one. Sods law of marine engineering states it is allways the last item looked at where the problem is.



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[maxi]

How about your raw water intake hose. They have a nasty habit of flattening themselves during suction, take off the revs and they return to their original shape - making it very hard to find the problem. This is an all too common cause for symptoms such as yours.

Even harder to diagnose is if the intake pipe is delaminating and a flap of rubber is closing the hose off, intermittantly.

Take this opportunity to put a new piece of hose on now, eliminating this area of doubt entirely - for just a couple of quid.

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[pete]

I have had the same thing with my Yanmar 1GM10 and have replaced the skin fitting and a few impellors over the last 3 years but without curing the fault, it only occurs randomly so you think it is ok until it happens again.
Now I think (fingers crossed) I have solved it, the skin fitting has the sea cock screwed directly to it and on to this is the strainer (roughly at water line level) with about 8 inch of pipe leading up to the engine water pump, the top of the strainer has a large clear plastic screw on cap with a O ring to seal it I have always put silicone grease onto the O ring and tightened as tight as possible by hand but have come to the conclusion that this has not been tight enough and the pump has found it easier to draw air from this seal rather than water ftom below the boat.

Hope this helps

Pete

<hr width=100% size=1>Artificial intelligence is no match for natural stupidity

 

[mowgli]

for what it s worth does your engine have a thermostat fitted?

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