Why is my coolant rusty?

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Righty Tighty

Righty Tighty

Blame it on the dog
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After just a few hundred miles on a rebuild, I’ve noticed my coolant is rusty. The level has held good, the car doesn’t seem to run hot. I plan to flush it out and add new coolant, but can anyone tell me what could cause this?

I used Prestone concentrate and added distilled water 1:1 to dilute it to 50%.

71 Scamp, 318, stock 22” radiator with a 16 psi cap, new heater core. Block was hot tanked prior to rebuilding.

E854461F-B5EF-488C-99C6-8C8EA92A4E36.jpeg
 
If it’s a new build, and been hot tanked/ cleaned by the machine shop, and you use a 50/50 mix of antifreeze and distilled water, I’m gonna say left over crud in the radiator working it’s way in to the system. Flush it refil and move on.
 
hot tanking helps, but it also needs to have all the passages scrubbed out with brushes before assembly. also could be dirty radiator, but who would rebuild the motor and not clean the radiator? :rolleyes:
 
Flushing is more than just running a water hose through it. A proper "flush" involves using chemicals to neutralize the rust/corrosion before it is flushed out of the system.
Takes a little time but it is worth doing it correctly or it will just do it again.
Your coolant mix and the use of distilled water is spot on.
 
Righty Tighty said:
Thanks! I’ll give her a flush and run it.
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It's flash rust from inside the water jackets. I always start a fresh rebuild with water and when it's broken in a bit I drain it and flush it and then fill it with 50/50 coolant.
 
kursplat said:
who would rebuild the motor and not clean the radiator? :rolleyes:
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Certainly not me!! Haha.

Well, I "flushed" the radiator very thoroughly with water, but as @MoparLeo pointed out, I didn't do it correctly. I hit the block pretty good with brushes before assembly, so at least I have that going for me.
 
I've heard of guys filling their cooling systems with EvapoRust. Running the car up to temp and then letting it sit over night. In the morning, drain it out and flush the block with water to get the rest of the EvapoRust out. My cooling system looks the same as yours on my Challenger. New radiator core. It's the flash rust from inside the cooling passages of the block.(like Mike said)
 
burdar said:
I've heard of guys filling their cooling systems with EvapoRust. Running the car up to temp and then letting it sit over night. In the morning, drain it out and flush the block with water to get the rest of the EvapoRust out. My cooling system looks the same as yours on my Challenger. New radiator core. It's the flash rust from inside the cooling passages of the block.(like Mike said)
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Thanks for the tip! I may try either that or the Therm-o-Cure. It’s good to hear that a) it’s nothing serious and b) other folks have experienced this.

I wasn’t too concerned since I’m not losing coolant and the engine isn’t overheating, but I was definitely surprised to see such a rusty mess.
 
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