How important to remove all old coolant?

[Winston]

I find it a real hassle to; drain, fill with distilled water, warm up car, drain, refil, warm up repeat. The drain and top up appropriate amount of coolant to equil 50% coolant.

I would rather just drain the radiator and top up with 50-50 every couple years. I am way under the 5yr 100k mile limit.

Is it really so bad to leave a bit of the old coolant in there?

 

[Ray H]

Probably not - unless the old coolant drains cloudy or with observable scale crud. My own comfort level dictates that I do repeated distilled water flushes until the effluent drains water-white clear. Life's not easy for perfectionists (or those who seek their advice...

).

 

[olympic]

Every engine I've ever worked on has a drain plug in the block to drain the coolant. 1 plug for inline engines, 2 for V engines. Some are tough to find though. If you drain the rad and remove these plugs you'll get 99% of the coolant out. Flush it with clean water while everything is still open and it's ready to be refilled.

 

[Buford T. Justice]

You can never remove all the old coolant unless you replace all components of the cooling system with new parts that have never been touched by any coolant.

The idea is to dilute the old coolant so much as to it being virtually gone.

 

[jmacmaster]

olympic is right. Put on some old work clothes, drive to the nearest dealer for your kind of vehicle, park near the doors where they drive vehicles in and out of the service shop area, and ask a mechanic to get under the engine with you and show you where the drain plug or plugs are.

 

[Tosh]

I don't want to get in trouble here, but if the old coolant looks in normal condition for its age, then maybe a fresh water flush isn't needed. Just drain and fill. Especially if you're replacing with coolant of the same chemistry. If the old coolant looks nasty, then you should flush, and keep an eye on why this might be happening.

 

[Matt_S]

I agree, Tosh. If you're well underneath the normal service recommendations, just a simple drain and fill should suffice. That's the approach I'm going to start taking. That way, I should never have any corrosion to worry about nor any reason to do any full flushes/chemical treatments.