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I have recently (yesterday) went through coolant flushing and this morning, I have opened the radiator cap and found something weird going on inside:


I'm pretty sure it was fully black all of inside but this is what I found this afternoon.

Any idea what is going on here?

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You're asking about the yellowy-brown spots? – Josh Caswell Dec 17 '13 at 9:10
Did you use a 'flushing additive'? Are the spots on the plastic, or do they come off with a finger wipe, or are they dis-colouration in the plastic? – Allan Osborne Dec 17 '13 at 11:46
I did not use any additives. I've only used demineralised water + coolant concentrate. I have tried rubbing them with a finger but it seems like the black bit is coming off and showing the metal under it. – James Dec 17 '13 at 13:24
you think that when you started flushing the system that the filler neck didn't look like that? – mac Dec 17 '13 at 18:21
It "may" have been like that prior to the flush but I do not remember it. I was more concentrating on the process of flushing as it was my first time. Also, I was flushing it in the garage, which has lesser light exposure. I've noticed the residue/peeling outside in the daylight. – James Dec 18 '13 at 1:22

Firstly, check the additive you have used is compatable with your engine. The deposits you have shown could be deposits in your cooling system, disturbed by the flushing of the system, settling back on to the surface you can see.

It is difficult to know exactly what the deposits are from the photo.

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The coolant concentrate I've used is the red long life coolant purchased from Toyota dealership (Car in subject is Echo 2003) and I assume all demineralised waters are same. I haven't put anything else in there. – James Dec 18 '13 at 1:43

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