Coolant: drain/fill or flush/fill?

I will soon change the coolant on my 07 4-cylinder 5-lug for the first time (90,000 miles).

On past vehicles I have drained, flushed with distilled water, drained, and refilled with mostly undiluted- usually Toyota red- coolant (knowing that even with draining from both radiator and engine block drains, some distilled water remained in the engine). But, I'm concerned this procedure with prediluted Toyota pink will leave me with a weakened coolant mixture that's too heavy on water.

So, I'm considering a drain and fill procedure. But, I'm concerned this will leave me with a weakened coolant mixture that has too much old coolant in it.

What do you think is the best procedure for a coolant change? Why?

 

I have pondered this as well. I don't have a really good answer. What I have done on the newer vehicles with the pre-diluted coolant is simply drain and refill a couple of times, with no flush. I do not introduce water into the cooling system. In this way, I am assured of only 100% pre-diluted coolant being in the system. On the other hand, it does not guarantee I've got all the old coolant out of the system, either.

 

Depending on how you travel you will be fine draining and flushing as you described. A 50/50 coolant mix gives freeze protection to around -30° to -40°F. Even if you had extra water left in the system when you added the premix coolant and ended up at 30/70 you should still be protected to around -20°F.

 

Thanks for the insight crazysccrmd. In the tropical climate of Houston, I don't have to worry too much about the lower temps. It rarely gets below +30 degrees F. I am more concerned about the cooling properties of the coolant. Summer can be pretty brutal here and stop-and-go freeway traffic is common, which can add to the heat stress on an engine.

 

Water specific heat: 4.2 J/g/C
EG(coolant) specific heat: 2.2 J/g/C

In other words, it takes almost 2x as much energy (e.g. heat) to raise the temperature of water 1 degree celcius. If cooling is your worry, more water will help you. Careful with using distilled water as it will attack the metal, water with nothing in it is like a puppy left alone in a room full of expensive furniture.

 

Maybe the answer is drain/fill up north and flush/fill in warm climates?

 

I ended up finding a copy of the FSM. It described a drain and fill. So, I went with that. I estimate 6-7 of the 9 quarts drained from the radiator and block.