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whistler49
whistler49

Posted: Thu Nov 09, 2017 4:42pm

Post Subject: Coolant quantity and change method

Hi I have just changed the coolant in my Vetus 4.17 42hp engine. I didn't know the capacity so measured the two skin tanks, allowed 1 gallon for the engine, and arrived at an expected 13 gallons approx. I drained by disconnecting the lower skin tank hose, opening the bleed screws and removing filler caps, pumping the bilge with an auxiliary bilge pump into containers for disposal.. I only drained half the expected amount out, and replaced the same amount (at 40% ratio) approximately 6.5 gallons. Would the full amount have drained, or does some get trapped in the skin tank baffles? I have asked my boat builder but so far had no reply. Useful tip, my friendly MOT garage disposed of the old coolant for £20, council disposal sites having no facility.

Tony-B
Tony-B

Posted: Thu Nov 09, 2017 4:58pm

Post Subject: Coolant quantity and change method

It all depends upon how the baffles are fitted and how close a fit they are to one skin. From what I can gather the edges of the skin tank is welded to the inside of the hull and then the baffles are also welded to the hull. Then the inside skin of the skin tank is welded to the edges. This means there are not welds on one side of the baffles so as long as the small gap has not rusted up even vertical baffles should drain given time. Did you use the engine block drain plug? If not some will be left in the engine but probably only a litre or so. I think that you may well have overestimated the engine capacity. Did you allow for the thickness of the skin tank edges and inner plate? If they are 6mm - 1/4" it reduces the volume somewhat. Did you blow through the bleed so you pressurised the skin tank a little. If air easily blew straight through I susepect you did drain the tanks.

whistler49
whistler49

Posted: Thu Nov 09, 2017 6:18pm

Post Subject: Coolant quantity and change method

Thanks for the reassuring reply - I didn't blow through, nor did I allow for material thickness. It is the first coolant change on a three year old boat, so shouldn't have a rust problem in the tanks. All seemed well after a test run of 2 hours, followed by a top up the next morning. Now I know what to do I'll ensure a 2 year change next as recommended.

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