Sam T

Hmmm sounds healthy.....

It wasn't blue, more like orange than anything else I think, though I am quite colour blind so not the most helpful person to be assessing! In which case I may have flushed it prematurely, but the boat's 20 years old and no idea when it was last done, so would rather have peace of mind and the knowledge of how to do it for future. I'll be replacing with blue because that's what I've already got and don't want to fork out again, but maybe I'll flush out and upgrade in a few years ?

Think that solves it. I ran the engine when I got home tonight. Didn't run it for that long so most of the skin tank was still freezing. But there were areas of it below where the bottom hose is that were getting slightly warm, and the return hose itself was still freezing, so definitely going through some channelled route rather simply top to bottom. In which case, flush it from the top until the bottom runs clear and good to go with whatever antifreeze I want. Thanks all! That combined with having topped up with fresh water, and run the engine a few times to flush out the engine itself, pipework and calorifier coils ought to be enough to change antifreeze right? Potentially one more fresh water top up once I've completely flushed the skin tank?

Yes that could make sense if that were the case. I suppose a way to tell could be to run the engine with just water in it until it's fully up to temperature and see which bits of the skin tank get hot and in which order? If the water in the lower half of the tank is still getting warm (though still cooling as it approaches the return pipe from whatever direction that may be) then it must be circulating via that point and flushing it through with a hose should do it? I did a version of that yesterday (not with that logic in mind) just to make sure the tank was getting hot and no air lock at the top. It seemed as though the water upwards from the bottom hose got hot quite quickly, with the water below only warming up very slowly from the furthest point away from the return hose (to the right and diagonally below) I'd guess this may mean it is circulating via the bottom, rather than the lower water just getting warm from being in proximity to the top, but I may not have run it for long enough to make sure of that. Does that make any sense? Largely guess work.

Thanks both, that was my thoughts exactly WotEver. Frahkn - Yes, I've connected it all back up with just freshwater for the time being while I decided what to do next, but once I've drained it down again will be able to pour water through the top and out the bottom. I assume it would run through clean if I did this manually but will try it out. I just wasn't sure whether through time it could mix with whatever is left in the bottom of the tank (not sure how much this is but potentially quite a few litres) and cause a bad reaction if it turns out to be the wrong antifreeze combo?

Hi, having read several posts on here about doing it, I had a stab at draining down my engine coolant this weekend. Most of what I was reading advised disconnecting the bottom hose of the skin tank and getting it out from there one way or another. My concern is that the lower hose connection is a little over half way up the tank so that isn't going to be draining it down to the bottom. There aren't any other access points besides the bleed valve (which is too small to get a pipe down) so I'm not sure how to get the rest of it out. I put a siphon pump in through the bottom hose connection and got some more out that way. But because of the angle of the hose connection point, I have very little control over the direction the pump hose is pointing once I've got it in the tank, so it almost certainly isn't going down to the bottom. The very last of the stuff I managed to get out was a bit dark and mucky looking (don't know if that's normal) which possibly implies it's coming from near the bottom of the tank?? However I only got about 25l out total, plus a little spillage to mop up in the engine bay. I know how big a skin tank is, is always a bit of an unknown but this didn't feel enough to me. The calorifier loop and engine contents are definitely drained as well, so all that could be left is definitely in the bottom of the (one) skin tank. I have absolutely no idea what antifreeze was in there before so was aiming to flush it all out and replace with an ethylene glycol to avoid any risk of mixing. For now I have refilled with just water and bled, so I can run the engine and circulate it a bit more before draining again and refilling with the antifreeze when I get a chance in a few days time. I'd be interested in anyone's thoughts as to whether it is ok to add this in, given I don't know what was in there before, and I doubt I've got absolutely all of the old stuff out. Likewise any advice on getting it out of the bottom of the tank below the bottom hose connection would be v helpful. Thanks in advance! Sam