My cooling system is quite nasty and needs a flush. I followed instructions on radiator flush, which said to run the car no more than an hour. However few tutorial videos online suggest running radiator flush for few hundred kilometers.

Understandably bottle instructions are more reliable source to follow but what happens when you run it for too long?


Radiator flush isn't anything magic. It is just a corrosive liquid that attacks everything in contact with it, to greater or lesser extent.

You hope it dissolves the blockage before it makes a mess of anything critical like the cooling passages in the cylinder block or the inside of your water pump, or it dissolves a hole in the radiator itself. (Old radiators are sometimes only held together mainly by gunk, and removing all the gunk is quickly followed by a leak!)

Leaving in the cooling system for hundreds of km is ridiculous, unless there was so much gunk in there that dissolving it all completely neutralized the flushing chemicals - which isn't a risk worth taking.

  • A big +1 for this. Manufacturers instructions ought to always be given more precedence than an online video. Dec 30 '19 at 8:25

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