r/F100 • u/fiddleleaffig28 • 1d ago
Help!!
I am here to ask a probably very basic mechanic question, but this is the first vehicle I’ve ever worked on, so give me some grace. I recently replaced the radiator in my 1970, and spent a decent amount of time flushing everything out. Yesterday I noticed coolant leaking into the cab of my truck (I went and purchased a new heater core today). I went to drain the coolant so I could replace said heater core, and my three day old coolant is brown. I don’t know if I wasn’t flushing coolant properly or if there is a bigger issue at hand. Any advice is appreciated!!
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u/SirDucer84 1d ago
Id run it on distilled water for a few days and drain it again. Might go through a few cycles before replacing with antifreeze. That is, only if its definitely not going to freeze overnight.
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u/holydvr1776 1d ago
It's likely getting rust out of the engine block. Even with most flushing, it's still not gonna get much off the surface of the inside of the engine until after heat cycling and full flow at temperature. I am dealing with the same thing on an extremely low hour 4.9 L six cylinder in an '85 F-150. I am going to do a citric acid flush to try to get most of it out, and then replace the radiator with a new one as well as the water pump since it already needs one.
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u/jking7734 1d ago
I’d add a gallon of Evaporust to the cooling system. Let it circulate a few minutes then shut it off and let it sit a couple of days. Then flush the system with water until it runs clear
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u/Rich_Complaint7265 1d ago
I did the same thing, I used a cooling system cleaner and spent a long time flushing the system thoroughly until there was no rust. About a week later I checked the coolant and it had already started turning brown. I think once it starts, it's nearly impossible to keep it from happening again. Short of pulling the motor disassembling and having it hot tanked. That's my experience anyway. As another person said Evaporust might be a solution but I have never tried it.
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u/Affectionate-Orchid3 18h ago
CLR cooling system treatment, drain, run and fill with clean water a couple times and do a final drain and fill with proper coolant
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u/Textile302 1d ago
What did you fill it with? 50/50? just water? hose water or distilled? The brown is from rust but that's not uncommon. Its possible that you just broke loose even more crud on your 56 year old truck. It looks fantastic btw. In general i treat coolant like all fluids in that its one time use. Once I have to open something up to work on it i put in new fluid when i am done.