If this vehicle originally came with the orange-color, 'long life' coolant
(Dexcool, I believe is one of the brand names), and regular ethylene-glycol
green coolant was later added, that could explain the brownish color. Mixing
the two is considered a bad idea -- and not only because of the resulting
color... Google the archives of this group for more details -- the subject
has been discussed at length a year or two ago.
I just took another look (i Hate those -20C temps :)
It seems like miniature rust particles, my guess is it's overdue for a
coolant flush. (might also explain why the engine runs cold and takes
about half an hour to get to 22C in the car)
BTW, the green stuff goes in there according to the owner's manual.
It could also be that at some point before you owned it, someone had
put in Bar's Leak or other radiator sealant. You didn't say how may
miles on it either. If a lot of miles on the car then maybe it's just
radiator sealer. In any event I would flush it all out.
Like X-Eliminator said, do a complete flush on your system. meaning take all
your hoses loose, and run water straight through the block till it comes out
clean. Do that with the thermostat out, and use the thermostats hole as the
water inlet. That will allow you to back flush the engine.
Then run straight water through your heater core, and "backflush" it.
Meaning run water through the hose that came off the bottom of your water
pump. That will help to dislodge any particles that might be in there.
Then while your hoses are off of the radiator, run fresh water through the
inlet hole and let it run out the bottom till it comes out clear. I let the
water run into a bucket just to see if any particle settle out. If I see
particle after the water is clear, I keep flushing till no more particle.
When yer done put it all back together... I did this on a 91 Ford Bronco
last spring, and some of the lines were so full of deposits it took me
almost 2hrs to flush the whole system. The bronco owner hasnt had any
complaints since then, she even said the truck runs better during cold
weather now. Her intake heater lines were plugged with mud, and the amount
of crap that came out of her block was phenominal. A good flush does an
engine real good.
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