Harry m Posted November 10, 2020 Share Posted November 10, 2020 I would like to flush out the cooling system on the 90 it’s a 200tdi 1991 vintage, is a case of just draining and filling with clean water a couple of times until it’s clean coming out or is there a procedure I need to follow Quote Link to comment Share on other sites More sharing options...
Ex Member Posted November 10, 2020 Share Posted November 10, 2020 If you want to do a good job run a cooling system flushing fluid, then flush out fully with clean water. 1 Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted November 10, 2020 Share Posted November 10, 2020 Oxalic acid is what is in the small bottles of radflush, but you can buy it in bigger bags cheaply on Ebay, also sold as wood bleach. Four heaped desert spoonfuls into the radiator should do you well, run it up to temperature, a good hard drive for 20 minutes, or maybe a bit more. You could remove the thermostat, which will help get the stuff round the system. Then, when cool enough to drain (i.e. it won't melt the skin off your face when you open the rad cap), drain (it will look ugly), and flush as well as you can. Take all the hoses off at one end, remove the thermostat if you left it in, and flush with a hose repeatedly until the water runs nice and clear. Don't forget the heater core, as this acts as a trap for sludge. If not too much trouble, remove the rad, and back flush it after this, and no-doubt you will get more out as well. 1 Quote Link to comment Share on other sites More sharing options...
monkie Posted November 10, 2020 Share Posted November 10, 2020 Also, when you drain the radiator don't forget to also drain the block by undoing the block drain screw near the dipsick tube on the block. It holds quite a bit of additional liquid that otherwise would just be recirculated when you filled the system back up. 2 Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted November 10, 2020 Share Posted November 10, 2020 Yep, good point, I don't do much with the black stuff, so hadn't remembered that. Quote Link to comment Share on other sites More sharing options...
Harry m Posted November 11, 2020 Author Share Posted November 11, 2020 Thanks for the reply’s I’ve ordered the Oxalic acid and will be on it when it turns up, I was thinking of dropping the coolant out and taking the stat out filling with clean water ready for when the oxalic comes. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted December 2, 2020 Share Posted December 2, 2020 Sorry, but I think that you may regret following that procedure. Adding oxalic acid crystals into your radiator, already filled with water, will result in a VERY concentrated solution locally, and it could cause problems. I think you'll be far safer by filling the cooling system with cold water and then draining a couple of litres out into a plastic bucket. Dissolve the acid crystals in the water drained and slowly add this into the header tank just after you have started the engine from cold. This will ensure that the acid is well distributed and you'll quickly have a full cooling system and can then make the drive recommended above. Mike Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted December 2, 2020 Share Posted December 2, 2020 Honestly, oxalic acid is very mild, but very effective on rust and scale particularly. I've flushed many a system in the way above, and never had an issue, straight into the header tank. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted December 4, 2020 Share Posted December 4, 2020 Good job that I'm not a chemistry teacher! Mike Quote Link to comment Share on other sites More sharing options...
muddy Posted December 4, 2020 Share Posted December 4, 2020 Just don't leave it in, I've done this recently, life has got very busy, I forgot to drain it, when I started it up to recirculate before flushing after 10 mins about 1500-2000rpm to warm up (its on axle stands) the top of the heater matrix let go, seems the matrix has blocked up, yet to investigate anything else as I just turned it off and left it. Quote Link to comment Share on other sites More sharing options...
Sigi_H Posted December 4, 2020 Share Posted December 4, 2020 Just a remark and a question as well. Why not remove the thermostate and flush from the beginning the radiator too? The procedure will be a lot shorter and I can be sure, that the radiator will be flushed too. Quote Link to comment Share on other sites More sharing options...
Harry m Posted December 5, 2020 Author Share Posted December 5, 2020 I drained off the coolant and removed the thermostat filled back up with clean water then added the oxalic acid ran it up to temperature drained and flushed out as far as I can tell all is well 1 Quote Link to comment Share on other sites More sharing options...
western Posted December 5, 2020 Share Posted December 5, 2020 Did you drop the coolant from the block as well, because it holds quite a bit. Quote Link to comment Share on other sites More sharing options...
Harry m Posted December 6, 2020 Author Share Posted December 6, 2020 Yes dropped from the block gave it a really good flush out with the hose pipe until it ran clean 1 Quote Link to comment Share on other sites More sharing options...
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