When removing the radiaor cap I beleive the coolant should be a clear colour, in my case a clear pink colour.

However looking under the radiator cap, as you can see in the picture, I can see a kind of brownish top layer. What is this/is causing this? There was previously green coolant in then so I imagine it could be a mix of the green and pink however shouldnt then it all look that colour rather than just that top part?

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  • 1
    Is this in your Honda? If not, what vehicle (year/make/model/engine)? Has the coolant been changed in it before? Also, if you really want to see (and show) what color the coolant is, take a couple drops out and put it on a white paper towel. Seeing it inside the radiator, the color can be deceiving. Nov 17, 2018 at 15:09

2 Answers 2


That coolant has oxidised over time.

It needs testing to see if it will still protect your cooling system down to the required temperature. If it does not, then it needs replacing. Just about all good mechanics or good garages have that measuring device.



  • Just one word? Come on you i've seen that you can do better than that.
    – MadMarky
    Dec 17, 2018 at 9:24

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