Rad replacement - coolant flush necessary/useful?

[donkmeister]

If I am replacing a radiator, water pump and the assorted hoses, is there any real benefit to flushing the cooling system or does enough coolant drain that it's generally not required?

I've had no issues with the heater matrix, kicked out loads of heat in winter. Rad change is purely preventative; it's got a trans cooler built in and they have been known to corrode through and lunch the gearbox.

I've seen a variety of videos on YouTube including one where Chris Fix flushes the system multiple times with the heater going, and another where Scotty Kilmer just blasts his garden hose in both directions through the cooling circuit. Nice to have clear coolant but I don't know if sludge is really that prevalent on a car.

[Tyre Smoke]

I've always been the stick the garden hose in and reverse flush it. Never seen much crud come out except on a 1970 Ford Crossflow. Modern stuff? Not sure I'd bother. They all run coolant with corrosion inhibitors these days.

[donkmeister]

It's a 2000s Lexus with OAT coolant, so modern(ish).

Righto, I'll try the garden hose backflow if it looks like I can do it without getting water in places I shouldn't. Otherwise I won't bother.

Cheers!

[GreenV8S]

I don't think flushing is important unless you have other problems causing contamination in the coolant.

It's worth minimising coolant loss to minimise the amount of air you have to deal with when you refill, but I guess if you're replacing the pump you will be completely draining the heads anyway. Don't drain any further than necessary though.