Radiator drain? What is really draining?

[Reggaemon]

I never flush my cooling systems but just do a radiator drain and overflow tank cleaning twice a year. I've been doing this of all my cars over the past 15 years and have never had a cooling system problem. Even my dex cool 3.1 chevy didn't suffer from the hg problem.
But it got me to wondering about how much coolant gets drained when just the rad drain plug is pulled. Doesn't some coolant get removed from the engine block? Does it get removed from the cooling passages in the heads? The lower rad hose has coolant flowing out of it so it must be coming from somewhere else and not just from the rad. So just how much coolant remains in the engine when only a radiator drain is done?

 

[LargeCarManX2]

I would think about 50%

If you want to purge the system without the big hassle. It takes a little time....(cool down) but after you drain the radiatior, fill it back up with distilled water. Run the engine to full temp. Drain the radiator again, after cool down....fill with your antifreeze mix of 70% antifreeze and 30% distilled water.

Otherwise, I would not worry about anything. Its like changing oil, you can't get out all the old oil if you tried. Really a non-issue in my opinion.

 

[duaneb9729]

in my s-10 pick up with a 2.2 four banger i drained my radiator and got 3/4 of a gallon of the two gallons it holds.

i am going to use your system to maintain my truck, although i just bought it last may and did a complete flush

 

[Al]

Originally Posted By: Reggaemon
I never flush my cooling systems but just do a radiator drain and overflow tank cleaning twice a year.

Yikes. Don't worry about a thing. I would guess that 75%+ gets drained. Maybe more if you point it downhill.

 

[Donald]

You probably also have engine drain plugs although harder to find and get to. The engine drain plugs should be not to far above the bottom of the block where the oil pan bolts on. However if they have never been removed, then they may be difficult as they are brass screwed into cast iron. In a V engine you would have one on each side. This still will not get all the old antifreeze out as there is still some in your heater core. And vehicles like my Suburban have a second heater core in the rear and long lines to get to it.

I think the best bet is to drain and refill the radiator once a year which refreshes the system with hopefully 50% new antifreeze.