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Q: Black coolant - no oil

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I drained the coolant in my car and replaced it with distilled water and some coolant flush. I went for a drive then drained that coolant again, it looked fine. still kind of pink/ red. I filled the cooling system back with distilled water and went for a drive again, came back and let the car cool. I drained that water and it came out black. There was no oil in it(I made sure that there wasn't) and it was just cloudy. The reason I know it isn't oil is because I put that water in a container for recycling and let it sit overnight, it has not separated and there is no sludge on the top. I filled the car back up with coolant to be safe and I have yet to see what color it is now. Do you have any Idea why it came out black? I also installed an aluminum water temperature adapter so maybe that has caused some rust. could it be that the distilled water has reacted with the hoses or aluminum in the car? In the manual, it says to not use water alone... Maybe that's why.

A: Hello. Black or cloudy coolant can be cause...

Hello. Black or cloudy coolant can be caused by excessive rust or corrosion, or contamination in the cooling system. If the cooling system hasn’t been flushed or serviced for a long time, it may take a few cycles of flushing to get all of the contaminants out. Black coolant can also be caused by worn hoses that have decomposed and have now begun to break apart and contaminate the cooling system. I would examine the condition of all the cooling hoses, removing them if possible, to also examine the internal condition of the hoses. If you need assistance, a certified mobile mechanic from YourMechanic can visit your home or office to inspect the problem and flush your cooling system.

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