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What's the best way to drain the engine coolant?

I need to change the engine coolant in my Isuzu 42 hp engine as it is of unknown vintage. There is no separate tap or drain point to do this, so I have to remove the hose attachment from the bottom of the skin tank. But the bilge will then be filled with a large amount of toxic liquid, so cannot be just pumped overboard. What are the best ways of extracting and disposing of the old coolant easily and efficiently?

Asked by: Rod Nelson  | 12.45pm, Wednesday 3 October

WW says:

Unfortunately this is something that boatbuilders seem to ignore! On the plus side, once you have emptied the coolant, you can add a t-fitting with a drain valve (and a tools-te-remove plug) where the lower pipe enters the skin cooling tank to enable you to remove coolant in the future with a hand pump.
Unfortunately, the procedure you describe is the only one you can really do. If you can isolate the bilge pump and then use a wet-vac to suck the coolant out of the bilge for disposal at an authorised disposal point ashore (usually at a local authority waste disposal site). You may be able to drain some of the fluid from the engine into a container from the calorifier pipework- and then remove the top host from the coolant tank and inster a narrow-bore hose, using a drill powered pump to remove the coolant, but this doesn't always work- especially is there is an internal baffle (if the hoses are both ends of the tank, then its likely there is an internal baffle- if opposite ends top/bottom then usually no baffle).
Sorry about that but there is not other way- but hopefully you will be able to make life simpler in the future for yourself. It amazes me that boatbuilders are often so short-sighted when it comes to general maintenance of the craft they build!

Mark Langley  | 3.27PM, Wednesday 3 October

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