Coolant was mud-brown????


In preparation for a long enduro next month, I decided to drain and flush the cooling system. As I removed the expansion tank cap, the guts of the cap stayed in the neck but the cap cover popped off. I’ve seen this before, and have a new cap and expansion tank coming. I got too aggressive getting the cap guts out of the neck and dinged it some. Plus, the expansion tank is 23 years old so replacing it is a good idea.

To my question - I thought the coolant was just water but it came out mud-brown. There was no coolant odor so I’m wondering what could have caused this. The “mud” is somewhat sticky but flushed fairly well from the block, expansion tank, and radiator.

Any ideas?




Is there reason to believe that you were looking at something other than rusty water? Water wetter is supposed to inhibit rust, but I only use about a half bottle and I have a really big radiator so it gets diluted a lot. My perception is that it takes very little “wetting agent” to do it’s thing, but I bet that in order to inhibit rust one needs a higher concentration of the stuff.

My radiator water always looks pretty brown.


Brown=rust. That is why anti freeze has rust inhibitors. I usually run two bottles of WW when I change water.