Does anybody have experience with testing and re-using
engine coolant?

After a very long time I need to pull the radiator out
of my Scout, get it fixed (leaky solder joints mostly)
and refill. The old coolant (conventional green Prestone)
looks reasonably good. The radiator is clean inside, the
coolant is clear. Specific gravity is low.

New coolant is more expensive than I remembered, and
getting rid (legally) of the old stuff is harder than
it used to be. Simply adding more antifreeze to make
the specific gravity correct is trivial, but I wondered
if there might be more sophisticated tests to detect
more subtle problems like pH. The original mix used
distilled water, so total dissolved solids are likely
to be OK. The major worry is the state of the corrosion
inhibitors. Ordinary pH test papers are subject to
cross sensitivity, so it'd have to be checked for
use with coolant. Web searches for coolant testing
found only specific gravity testers, nothing about
pH or other chemical tests.

Thanks for reading, and any stories!

bob prohaska

On 03/08/2021 05:14 PM, bob prohaska wrote:

The old coolant (conventional green Prestone)

My '86 Toyota came with red coolant.

The original mix used distilled water, so total dissolved solids are
likely to be OK.

I used tap water when I replaced the red with green. From Santa Clarita
Water Co., ****tiest water in the Antelope Valley.

The major worry is the state of the corrosion inhibitors.

The Toyota's aluminum cylinder head apparently didn't appreciate having
green coolant, or the ****tiest tap water in the Antelope Valley.

Web searches for coolant testing found only specific gravity testers,
nothing about pH or other chemical tests.

I should have stuck with Toyota's red coolant.

Thanks for reading, and any stories!

Extreme engine overheating even while cruising in 5th on a level
freeway, on a cool night. Lots of aluminum was missing inside the head.
Couldn't find a replacement 22R head at the time, only 22RE heads, so
the shop TIG'd more metal in to fill the holes... allegedly. Whatever,
that fix didn't last. Struggled to reach 100K miles, and traded it in.

On Tue, 9 Mar 2021 01:14:50 -0000 (UTC), bob prohaska
wrote:

Does anybody have experience with testing and re-using
engine coolant?

After a very long time I need to pull the radiator out
of my Scout, get it fixed (leaky solder joints mostly)
and refill. The old coolant (conventional green Prestone)
looks reasonably good. The radiator is clean inside, the
coolant is clear. Specific gravity is low.

New coolant is more expensive than I remembered, and
getting rid (legally) of the old stuff is harder than
it used to be. Simply adding more antifreeze to make
the specific gravity correct is trivial, but I wondered
if there might be more sophisticated tests to detect
more subtle problems like pH. The original mix used
distilled water, so total dissolved solids are likely
to be OK. The major worry is the state of the corrosion
inhibitors. Ordinary pH test papers are subject to
cross sensitivity, so it'd have to be checked for
use with coolant. Web searches for coolant testing
found only specific gravity testers, nothing about
pH or other chemical tests.

Thanks for reading, and any stories!

bob prohaska


Filter it and buffer it. The chemicals are available. 10.0 or 10.5 ph
buffer. I have been using a bottle of Sodium Borate 10.0 reference
buffer solution I got from a chemistry proffessor neighbor.

Or buy Prestone Command SCA