97 4.6 f150 with 174k miles

Why is it so brown after so many flushes?

I flushed it 30 months ago with preston coolant and distilled water.

 

Ford's use a gold coolant, which may turn to a brownish colour. What colour coolant did you use last time it was flushed ?.

Is the block cast iron or aluminum, iron could be rust. Any signs to indicate a head gasket leak ?.

 

Preston has a habit of not staying green.

The previous owner of my car used Preston and the coolant in my overflow bottle was orange/brown. Drained/filled twice with Honda Type 2 and my coolant is now perfect.

 

If it's like my truck (dodge dakota v8) when you drop the coolant it doesn't drain nearly the entire block. I doubt you actually "flushed" the coolant though? Maybe I'm wrong but I'm pretty sure most people don't actually do a flush, they just drop the coolant and replace - a couple times. For my truck it pretty much only drains the radiator and that it - at least half of it is left behind. There's two nipples on either side of the motor that I could open but they can become bad leak points so I didn't bother.

I put in prestone to my truck to replace what was in there which was the GM stuff (about 30k miles on it) and when I did that it definitely turned a brown color. Not a big deal though, I just left it that way. It's doing it's job just fine and then some.

I would never put prestone in my F22C (Honda Type-2 only), but there's really no problem with the prestone in my opinion for most motors. In fact I think it's pretty good stuff.

I can't see your pics at work but I imagine you're fine.

 

I change out the Prestone extended life coolant in mine every five years or so and it stays the same color. I am guessing the brown is a contaminant.