Recommended 2 year interval, I've extend to 3, due to the very high
quality of our water, lacking nearly all mineral content, and being
very nearly distilled. Changes too often will introduce excessive
corrosive agents and other contaminants, which after a period of
reactivity (and damage) will dissipate, leaving the coolant ideally
chemically "dead".

The changing procedure is covered on pages HT-6 and -7 of volume 2 of
the repair manual. I find the description deplorable, and to this day
wonder what's intended. I believe it's an attempt at purging all the
air from the system in one refilling operation. Let me say
emphatically, that this is simply IMPOSSIBLE, and be prepared to
top-up the coolant after each operation, much more at first and then
lesser with time until the level becomes stable.

Other informed perceptions on this most welcome & thanks ! ...

"Steve Giannoni" <casagiannoni@optonline.net> wrote in message
news:mldjl2dt8ov8kl9tm2jhsf1i858f7e155d@4ax.com...
> Recommended 2 year interval, I've extend to 3, due to the very high
> quality of our water, lacking nearly all mineral content, and being
> very nearly distilled. Changes too often will introduce excessive
> corrosive agents and other contaminants, which after a period of
> reactivity (and damage) will dissipate, leaving the coolant ideally
> chemically "dead".
>

I believe that the coolant replacement interval is 3 years for the original
factory fill and 2 years after the original factory fill has been replaced.
The original factory fill is diluted with distilled water and the
maintenance interval assumes that the replacement fill is diluted with tap
water. If you use distilled water (as opposed to tap water or "nearly
distilled) water, then you could stretch the replacement interval to 3
years.

> The changing procedure is covered on pages HT-6 and -7 of volume 2 of
> the repair manual. I find the description deplorable, and to this day
> wonder what's intended. I believe it's an attempt at purging all the
> air from the system in one refilling operation. Let me say
> emphatically, that this is simply IMPOSSIBLE, and be prepared to
> top-up the coolant after each operation, much more at first and then
> lesser with time until the level becomes stable.
>
> Other informed perceptions on this most welcome & thanks ! ...

I don't have an opinion on the procedure for replacing the coolant. To be
honest, the only car I've actually read the coolant replacement procedure on
is for the MR2, due to the front-mounted radiator and mid-engine location.
--

Ray O
(correct punctuation to reply)

No, I think it's always 2 years, even for the first change, which I
did at 2 years, both electrical and ICE coolants. This begs the
question as to why any change is necessary assuming you use distilled
(or nearly distilled) water. After the 3 years the exiting electrical
coolant fluid looked completely clear and free of any sediment. The
drain plug which is at the lowest point has a substantial hollow
recess facing up which had nothing in it and the whole was bright and
clean from the gasket on in. Haven't done the ICE coolant yet.

Interesting / important "self-note" from 3 years ago :

On page CO-2 of the 2001 Repair Manual Volume 2, the location of the
engine coolant drain plug is referenced " … engine drain plug on the
engine coolant drain union ( on the right front of the cylinder block
), …", and includes a sketch showing the engine and the "Engine Drain
Plug" as a strange looking item floating somewhere sort of on the
mid-right side of the engine, facing toward the rear of the car. I see
now that Toyota's right and left side of the engine is as facing
forward in the old conventional drive configuration, so in the Prius,
the engine's right side faces toward the rear of the car. But now,
they seem to get it reversed with the "front" of the engine being the
drive end. Go figure! I'd be embarrassed to reveal how long I hunted
for that @#*&*&% plug on the wrong side of the engine.

"Steve Giannoni" <casagiannoni@optonline.net> wrote in message
news:vqjkl2h4ca82h7fdafb1p3khbrtk5e61np@4ax.com...
> No, I think it's always 2 years, even for the first change, which I
> did at 2 years, both electrical and ICE coolants. This begs the
> question as to why any change is necessary assuming you use distilled
> (or nearly distilled) water. After the 3 years the exiting electrical
> coolant fluid looked completely clear and free of any sediment. The
> drain plug which is at the lowest point has a substantial hollow
> recess facing up which had nothing in it and the whole was bright and
> clean from the gasket on in. Haven't done the ICE coolant yet.

You can safely stretch coolant replacement to 3 years if you dilute with
distilled water. Just keep an eye on the coolant, if it gets crudded up
before 3 years, change it.

>
> Interesting / important "self-note" from 3 years ago :
>
> On page CO-2 of the 2001 Repair Manual Volume 2, the location of the
> engine coolant drain plug is referenced " . engine drain plug on the
> engine coolant drain union ( on the right front of the cylinder block
> ), .", and includes a sketch showing the engine and the "Engine Drain
> Plug" as a strange looking item floating somewhere sort of on the
> mid-right side of the engine, facing toward the rear of the car. I see
> now that Toyota's right and left side of the engine is as facing
> forward in the old conventional drive configuration, so in the Prius,
> the engine's right side faces toward the rear of the car. But now,
> they seem to get it reversed with the "front" of the engine being the
> drive end. Go figure! I'd be embarrassed to reveal how long I hunted
> for that @#*&*&% plug on the wrong side of the engine.

The repair manuals use SAE conventions when referring to the front, sides,
and rear of the engine. These conventions are not the same as conventions
for front, sides, and rear of the vehicle or engine bay.
--

Ray O
(correct punctuation to reply)