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Yes, there are 3 kinds of coolant "bases" now, color is not always an indicator as to which is which.
The original coolant, after straight water of course, lol, is silicate based, this was usually green.
Silicates bond to metal parts inside the cooling system to prevent rust and corrosion.
Silicates start to break down after a few years of use so it was recommended to change coolant every 2 years, the new silicates in the new coolant stabilized the old silicates, reducing the possible "gunk" it makes.
OAT(Organic Acid Technology) coolant was developed in the late 80's early 90's, it is usually red, this does the same bonding to metal parts but lasts longer, 5 years is the recommended change period.
Problem in switching between these two bases is that neither can stabilize what the other left behind, so switching can cause "gunk" build up.
Because these bond to the metal, flushing doesn't do much except clear out most of the already floating "gunk", which is good but with nothing to stabilize the bonded silicates or OAT it will turn to "gunk" over time.
There is now a 3rd base, HOAT, Hybrid-OAT, if you are not sure of what base was used before then this is probably the best choice.
HOAT is OAT based but has silicates added to stabilize any older bonded silicates.
Just as a heads up, radiators get clogged up pretty easily when coolant bases are switched around, the radiator is basically the filter of the cooling system.
New rads are $100-$150 and easy to swap out, I would swap out the rad as an insurance policy.
And even without changing coolant bases I would swap the rad every 80-90k, that's less that $2 per 1,000 miles, oil filters cost more than that.
You change the oil filter, the air filter, even the fuel filter, don't forget the coolant filter.
Last edited by RonR; 09-08-2012 at 12:16 PM.