Is it critical to change coolant at 100K?

[johnwk]

It wouldn't hurt to run a few gallons of distilled water through the system (following the same drain-fill-drive-drain procedure) before filling it with the new coolant.

I'm neither an expert nor a perfectionist, but I just used the Toyota-labeled Prestone stuff from the auto parts store.

A mini-tip: I found that only unscrewing the radiator drain plug part of the way prevented it from spraying all over the plastic under-engine guard (where it will collect and sit).

A word of encouragement for anyone considering doing this for the first time: changing my coolant following tmontague's instructions in another post was the first real job I ever did on any car ("real job" = something I would have normally paid someone else to do), and it really helped me to get over my fear of DIY maintenance.

[RMcG]

Originally Posted by johnwk

It wouldn't hurt to run a few gallons of distilled water through the system (following the same drain-fill-drive-drain procedure) before filling it with the new coolant.
.

I plan to use Toyota Brand Coolant, 1 gallon of pre-diluted 50/50 costs about $23 (USD). The capacity of the cooling system is 5.1 quarts, but I think that perhaps much less than 5.1 quarts (perhaps a gallon or less) drains out of the cooling system when you open the plug/stopcock for a standard drain procedure.

So I am thinking that replacing the old coolant with distilled water and running the engine for a few minutes and then draining again (as suggested by johnwk in the quote), would get more of the old coolant out of the system before it degrades.

QUESTION: Does anybody have any comments or suggestions about this?

Thank you,

R.

[RMcG]

Originally Posted by johnwk

It wouldn't hurt to run a few gallons of distilled water through the system (following the same drain-fill-drive-drain procedure) before filling it with the new coolant.
.......

A mini-tip: I found that only unscrewing the radiator drain plug part of the way prevented it from spraying all over the plastic under-engine guard (where it will collect and sit).

If I do decide to run distilled water through the system, how long should I let the system run in order to mix & help get the older coolant out of the system? Ten minutes? 20 minutes? Until the engine is hot?

(I know that there is the potential problem of diluting the coolant, since you cannot get all the distilled water rinse out of the system before you add the new coolant.)

Thanks,

R.

[johnwk]

Originally Posted by RMcG

If I do decide to run distilled water through the system, how long should I let the system run in order to mix & help get the older coolant out of the system? Ten minutes? 20 minutes? Until the engine is hot?

I would drive the car for a few miles, until it's warmed up, with the heat on full blast.

Originally Posted by RMcG

(I know that there is the potential problem of diluting the coolant, since you cannot get all the distilled water rinse out of the system before you add the new coolant.)

If you want, when winter approaches, you can do another quick drain-and-fill, which will reduce the dilution while also renewing a bit of the coolant. There's a very cheap and simple tool for testing the coolant dilution.

[RMcG]

Originally Posted by johnwk

I would drive the car for a few miles, until it's warmed up, with the heat on full blast.

Thanks John. But why is it necessary to put the heat on full blast?

R.

[johnwk]

Originally Posted by RMcG

why is it necessary to put the heat on full blast?

Having the heat on will make the water flow through the heater core, further rinsing out the old coolant. If the system is properly filled, the heat will stay hot through your ride. If it cools off, there's unwanted air in the system.

PS. In my experience, it takes quite a lot of "burping" the upper and lower hoses to get all the air out while filling the system. Squeeze them each slowly and repeatedly until you don't see any more bubbles at the radiator neck. And over the next week or two, double-check the levels at the radiator neck and the overflow tank. If there was air in the system that escaped, you'll need to top off the coolant.