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edstill 03-30-2009 05:26 PM

Ack! What did I drain?
Adventures in DYI!

I had to replace the hose returning fluid from my hot water heater to the heat exchanger on my Universal M25. In doing so I drained what looked like pink antifreeze from the HX, out of the wingnut-type drain. Grunts, goans, profanity- hose replaced.

Now I'm wondering if I drained antifreeze out of the raw-water side of the system, or if that was coolant in the fresh water side. If it was the RW side, should I replace the fluid before starting? And if its the fresh water side, I'm sure I have to replace it, but don't know how. Could someone give me a hand before I melt down my silver beauty?!


PBzeer 03-30-2009 05:33 PM

If it's raw water cooled, you don't use anti-freeze in the cooling system.

GreatWhite 03-30-2009 06:06 PM

I would guess the pink stuff is a non-toxic anti freeze added to the internal plumbing system to stop freezing of the pipes. Does this sound feasible?

arf145 03-30-2009 06:12 PM

If your boat was winterized by sucking pink antifreeze through the exhaust system, then pink would be in the heat exchanger. I think that is what you drained. If so, it will fill up next time you run the engine and the impeller forces raw water in there.

The two hoses between your HX and hot water tank is a closed loop of engine antifreeze--now that you need to top up because I assume you lost some antifreeze when you replaced the hose.

marinegirl405 03-30-2009 07:04 PM


Originally Posted by edstill (Post 468478)
I had to replace the hose returning fluid from my hot water heater to the heat exchanger on my Universal M25.

If you are sure about the hose, then yes, you must replace this liquid, otherwise You won't get hot water any more. Your boat has (I assume from your comments) a raw water intake, this flushes over your heat exchanger to help cool the fluids. Internally your engine is cooled by a separate, constantly circulating fluid, often called "fresh water" but it normally contains some coolant liquid/anti-freeze - hence the pink colour you are seeing.

So Separately from your raw water /sea water system, your heat exchanger is full of little pipes that are connected to pumping that fluid you just drained. The primary job of that fluid is to circulate around the engine and draw off the heat (separately the raw water then cools the fluid from these pipes in your heat exchanger).

On your boat you are using this "internal" cooling fluid for a 2nd job - You get free "hot water" since the circuit has been extended to your hot water heater from what you say... Of course you'll only get hot water if your engine has been running recently. Plain water is rarely used in these internal pipes due to the risk of freezing, but neither is 100% coolant/antifreeze either as this is actually a poor conductor of heat, and you wouldn't get your hot water... Normally it is a 50/50 mix of water and antifreeze. A little compromise.

I hope i've described that so it makes sense.

So - now you have to replace that liquid AND get any air out of the system (it will settle in the pipes at the highest point, and if you are lucky there will be a vent there). There should be an expansion tank/reservoir of this fluid somewhere near your engine (at least there is on mine) - you can simply top up into that little tank. It normally has a min fill level, and a max level - just fill to the min fill level and maybe 1/3 upto the max fill line - when you run your engine the fluid expands and then it might reach the max level. Run the engine for a little bit and make sure you've cleared any air pockets - check on the level and top up if necessary.

Separately when you winterized your boat (if applicable for your environment) you would ensure the raw water system is flushed through with antifreeze, so (I bet you can guess) it won't freeze and damage anything during the winter cold. But from what you say this isn't the hose you disconnected.

Good luck

edstill 03-30-2009 07:13 PM


Thanks for that. It goes right along with what I've just read after finding a manual for my engine online. (thank god for pdfs!)

I am in for a long season of feeling in over my head. And I cant wait!


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