Coolant draining from engine block

[james250]

So I need to do a coolant change, draining the radiator with pressure cap open just barely drains under 5L (including syphoning out overlow bottle) Now I know that there are supposed to be two drain plugs on each side of the engine block, but getting to these are a right pain in the backside. I've drained just under 5L and filled up new coolant. If I run this until engine is warm then cool the car down and repeat the radiator drain again, will that be sufficient? idea is to try and dilute the remaining 4 or 5L that remains in the engine block. By running the car and letting it warm up the new fluid should mix with the fluid in the engine block and then there should be a diluted mix in the radiator. So draining the radiator again and re-filling another 4 or 5L will that work?

[johnatg]

I had an is250 for 7+ years and never did find those block drains. After 10 years old I just drained what I could once a year and refilled. No problems and I think the car is still running fine at 15 years old. 

[GMG]

...did the same; drained from the radiator 'tap'; bled system and did a few journeys and then repeated the exercise. Reckon this is sufficient to clean the coolant...