Is it critical to change coolant at 100K?

[tmontague]

Originally Posted by voxtrot

Hi tmontague I am going to be doing a coolant drain and flush and replace the thermostat on my 2007 Yaris Sedan with Automatic Transmission for the first time. I just recently hit 160k miles and I do not think the coolant has been drained and filled before I bought it used. I am going to be USING THIS
with distilled water. I will buy two gallons to flush or more until it comes out clear. Once it is clear how do you know how much of the concentrate to add with the clean distilled water already inside? Manual says 5 Quarts for Auto.
I don't know if everything comes out in the flush so do you have to wing it a little when adding the rest? Since it is hot here now would it be ok to have a little more distilled water inside radiator or reservoir? I don't want to damage the coolant system or engine since this is my first time doing this. Also worried about the left over air pockets damaging system after.

Thanks

You won't ever know exactly how much concentrate to add - which is why you always mix a concentrated coolant with water before you add it to the car.

And that is also why I said you can just simply drain and re fill as you likely will not have any benefit of a flush.

If you are set on flushing it, then just run water through it until it comes out clear. Then start adding the coolant that you premixed in other jugs until the rad is full. Over fill the overflow reservoir a bit as well.

Squeeze the rad hoses a bit and you will see the coolant level drop a bit in the radiator. I typically jam a funnel in the radiator fill hole and over fill the funnel and then turn the car on, you will see the level drop a bit and then start to rise as it warms up. Once the car is off it cools and starts dropping. Go back after 30 mins and remove the funnel and top up the rad. Drive your car will an over filled overflow reservoir and check it every day as it will drop as air ir burped out of the system. This will stop after a couple days.

In my experience with various Yaris', they bleed air from the cooling system really well, just make sure the front end is jacked up so the rad cap is the highest point of the engine.

Once this is done you need to buy a tester to make sure the freezing point is well below anything that you will see in your climate. You will have more than enough coolant in there for the summer, but potentially not enough for the winter, depending on your climate. Most of the coolant is removed when you drain the rad, but a slight amount will still be left in there.

FWIW many people say you need the fan to turn on to open the thermostat - this is wrong and a waste of time. The T-stat opens at 180F, well before the fan kicks on (typically 204F). Also the Tstat is not an all or nothing mechanism, it will slowly open just prior to 180F and fully open around 180F. I have successfully bled cooling systems in ambient temps way to cold to get the fans to turn on.

I just finished draining and re filling my Subie Outback and when the fans actually kicked on the coolant level didn't even drop - this is because the Tstat was already wide open well before the fans kick on.