Modern coolants have enough corrosion inhibitors. Using tap water is just fine. Corrosion and sludge are usually when garages use weak mixtures to make the bulk coolant bottle last longer.
Ok, so just flushed with this, it says to use whole bottle but I used 1/2 as this if for up to 10L car system. Question is, should I flush with plain water again to clear it out after drainage? It doesn't say I need too
Well, I can't see it could do any harm to flush it out once more with plain water. Personally, I think I would, rather than leave any residue of whatever the flushing mixture is, just in case it can react with the new coolant, which is unlikely.
So far I have flushed with water, with the flush stuff and now with water again. I have also started and run a few times to change the oil. I do have a slightly funny rattle that has started from the top of the engine, almost sounds like a Ducati. I'm putting it down as old fuel (at least a year and also very low so bottom of tank) and maybe a bit of carbing where it is starting/stopping without really getting to a decent temperature like a good ride wood. Think I will have the tank off next week and throw the old stuff out and put fresh in. Also, some liquid coming from exhaust, i'm putting this down as condensation forming from it not really getting to a decent temperature. Can is off so probably noticing more than I would if it was on.
