Coolant changing colour, then back again!

[Papawads]

I use a yellow coolant by Bardahl, in my Yanmar 4JH3-TE engine; have done for three years. It's yellow when it goes in and remains yellow all season (viewed in expansion bottle).
This year, after running the engine, it turned brown. First run after service and first of the season. Then without running for a few days, became yellow again! Sure enough, ran the engine and its brown again!!
So I'm thinking... sediment? possibly very fine, as after one day it's still brown.

Possible cause... the only thing I did differently over winter, was to draw in an anti-freeze mix into the raw-water circuit, not coolant curcuit. Could the antifreeze have caused a chemical reaction with the metal, and affected both sides of the heat exchanger metal? Is that brown fine copper?

...and why do our American cousins spell colour with no U? Always been a mystery to me 😉

Thanks guys

[SY Harmony]

Originally Posted by Papawads

I use a yellow coolant by Bardahl, in my Yanmar 4JH3-TE engine; have done for three years. It's yellow when it goes in and remains yellow all season (viewed in expansion bottle).
This year, after running the engine, it turned brown. First run after service and first of the season. Then without running for a few days, became yellow again! Sure enough, ran the engine and its brown again!!
So I'm thinking... sediment? possibly very fine, as after one day it's still brown.

Possible cause... the only thing I did differently over winter, was to draw in an anti-freeze mix into the raw-water circuit, not coolant curcuit. Could the antifreeze have caused a chemical reaction with the metal, and affected both sides of the heat exchanger metal? Is that brown fine copper?

...and why do our American cousins spell colour with no U? Always been a mystery to me 😉

Thanks guys

Brown could also be oil being emulsified into the coolant, then settling out.

As far as the spelling of color, we’re to frugal to purchase the extra, unneeded vowel.

[JPA Cate]

My guess is that the reasons Americans don't follow UK spellings for words of French derivation is that over the years, spelling has been very fluid. We spell "center" like "enter"; most of the words terminating in "our" in the UK end in "or" in the US, and most of us recognize the meanings, regardless of whether it's the saviour's endeavour or savior's endeavor.

Now, as to the brown in the coolant, sounds like rust to me. And when you run it, it gets circulated around, and as you suggest, the particulates settle out over night. Fwiw, copper oxide is green, iron oxides are brown.

Ann