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Old 29-03-2015, 05:20   #1
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Leaking coolant from the radiator cap

I have a Volvo Penta MD-2040. I have been leaking coolant from under the radiator cap. The engine runs cool, instrument reads normal. The engine will leak out fluid and run fine when it reaches a level, 2 maybe 3 cups low. It is suppose to be filled just shy of the lip of the heat exchanger chamber. It runs well when just below where the core is visible.
Changed radiator cap, $94US. still leaks.

Today going to change the impeller, expect no change but it is time to do this maintenance, able to be certain that it has nothing to do with my problem. Also easy and cheap to do.

I think it might be the thermostat? Funny though that the engine is not running hot at all.

Thoughts as to what the problem might be?


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Old 29-03-2015, 06:34   #2
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Re: Leaking coolant from the radiator cap

Look closely at where its leaking from while engine is running. It could be the fill neck itself is leaking where it connects to the expansion tank or the flange on the fill neck is distorted/damaged so even the new cap wont seal.

Impeller and t-stat are unrelated.


BTW: radiator cap is a standard automotive cap (14 PSI IIRC)...no need to donate about $75 to Volvo...you can get one for about $20 at your local autoparts store.
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Old 30-03-2015, 04:18   #3
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Leaking coolant from the radiator cap

I cleaned the lip of the radiator where the cap sits. Lightly sanded with fine sand paper. Put the
Cap on and ran the engine for an hour at high idle. Not under load although before it would leak, did not this time. Sailing over Easter and am sure we will do some motor sailing. Good test then. I hope I can put a check off this chore.

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Old 06-05-2015, 03:43   #4
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Re: Leaking coolant from the radiator cap

It turns out that where the filler cap twists onto the radiator, that piece is pressed into the cast radiator. The neck that this pressed on, has come apart, thus it leaks. My local welder is going to make a piece to attach both back together. One piece is bronze / brass the other is cast. He has had prior experience. In his boat to get into the engine room, a good place to step is on the radiator, unfortunatly, once he stepped on the cap and had to make a repair similar to this one.
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