How can I get rid of brown coolant?

Nick1994

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Phoenix, AZ
3 years ago I replaced my radiator and flushed out the cooling system with some Prestone flush and 8 gallons of distilled water. Refilled with plain green coolant and distilled water at 50/50.

I've now just flushed it again the past couple weeks, I've put 15 gallons of distilled water through it. What I do is pull the lower hose which gets out 1.5 of the 3 gallon capacity and I then refill with distilled water. The first time I refilled with Prestone radiator flush and drove for maybe 2 hours. I had some soapy foam for a little bit to flush out after that.

It looks pretty clear when I pull the lower radiator hose, but I let it sit for a week and I changed the water pump, this is what it looked like when I topped it off (video below). It doesn't usually look this brown from the cap though.

My Jeep sees some offroad driving. Initially this was getting dirt from the dirt roads into the overflow bottle, which i fixed 3 years ago with a filter for the vent.

But it's still kinda brown. Is this still dirt? Rust? Once I get it clean I'll be using distilled water and Zerex G05 antifreeze (already bought 2 gallons).

 
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359
Location
Maryland
If you are on a municipal sewer system, just pour it down the toilet. Waste treatment plants have the bugs that chew up ethylene glycol.
 
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8,086
Location
MI
I agree with Snagglefoot. Use one of the heavy duty cleaners to clean and neutralize the existing rust. I've had good luck with the stronger of the two Zerex cleaners.

I bet one of those old Prestone backflush kits would be more beneficial in blowing all the crud out of the system too.
https://www.picclickimg.com/d/l400/pict/292043161472_/Prestone-FlushN-Fill-Kit.jpg

Then, get your new coolant in there as quick as possible.
 
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2,058
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Minnesota
Let it go, it's hardly even dark. It's just a small amout of particulate from rust in your water. Why fret over something so minor....your car won't last longer because you coolant has a bit of rust in it.....
 
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2,388
Location
Virginia
Wix 24019 coolant filter base,
Wix 24069 short coolant filter
or Wix 24070 long coolant filter

Install in the heater hose supply line...

 
When you let it sit for a week with no coolant in the water, it starts to rust immediately. I’ve seen this before. Flush it again and sacrifice a gallon of coolant in the flush water, then immediately put in your concentrated coolant so the numbers work out, and error to the high side with the concentration.
I agree, but you could also use a quality anti rust during the prolonged flush phase. Also, IIRC, long life coolant take a while to actually start protecting from rust, so you may want to add a quality anti rust in with the new coolant to protect it until the long life coolant takes over.
 
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Arizona
Looks like corrosion to me, too, probably from the mild acid in the flush plus then sitting with either plain water or plain water + air in a not-full system. Follow Snagglefoot or anotherTodd's advice.
 
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GA
I bought a car with a nearly clogged heater core. I used the flush products but the heater core was still slap full of what I'd call mud. I flushed and flushed and backflushed the core directly till it ran clean. The coolant still has a bit of a brown tint to it but it did not even begin to clear up until I did that. My point is flush the heater core directly if you can.
 
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Nick1994

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I ran another 1.5 gallons of distilled water through it for a total of 16.5 gallons and then topped off with Zerex G05 at 50/50 mix ratio.
 
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YYC
It was rust, the Jeep 4.0L I6 has an iron block so if you let it get low on coolant or don't change the coolant for a very long time the coolant passages will start to rust and that rust will be carried away by the circulating coolant when the engine is running.
 
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Northern New York
The 4.3 in my Mercruiser is raw water cooled like most. Every fall when I drain it I have to use a wire to get the rust moving for it to completely drain. Chunks always come out and always have. No issues with clogging whatsoever and the thing has 1300 hours / 30 years on it. The water pump lasted for 28 . So in your case I wouldn’t sweat the bits of rust floating about One bit.
 
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