Well if you look under to post titled dex-cool.
DO NOT THINK DEX-COOL IS A PROMISE OF GOOD HEAD GASKETS.
As a Tech I can also tell you that GM only put out 16 different supersesions of headgaskets but only 3 or 4 show as some are running changes.
And as for Dex-Cool being oh so great dont bet on it. Dex has a mix of 2 types of organic acids to control corrosion/erosion protection one is called sebacate and the other is 2-EHA.
Now for the short and crunchy version, 2-EHA is a plasticizer and can and will soften up plastic engine parts/gaskets it comes into contact with. This is much worse on some engine more than others.
Now if you want extended life antifreeze you can do a complete flush and switch over to G-05 and it uses a different chemistry and wont hurt anything. and if someone tells you the current technology seals in water pumps wont take the silicates in green antifreeze ,thats a lie as the carbide seals in todays water pumps are pretty much bullet proof unless damaged at time of install or there ia too much castingsand in the cooling system which has been found to be the big problem with damaged seals.
Now the reason you get rust mixing is because of system getting low then the coolant washing the corrosion away and it deposits its self in heat exchangers.
Oh and the silicates stay in suspension to curtail the eletrolytic process of mutiple metals and dual componnet coolant(if it isnt fresh it can become electrolyte,,, as it the cooling system becomes a battery) This is why we need to keep the cooling system in the PH neutral so it doesnt attack parts. If it goes acidic it simply eats on the sodt parts, it goes (too) alkaline it eats either the anode or cathode (I forget which way but it does) and I saw this happen in a big dodge van with 83 k on the odo it had a large hole ate into the water pump and let the coolant flow to not go through the engien and blowing a hose, I missed the hidden bypass hose that blew, and replaced the water pump butthen found it to have the bypass hose had blew because it over heating.
We had coolat test strips and while it was temp safe it literaly ate the ph test pad off the stick, and as such the aluminum of the water pump.
Oh and it may not hurt the aluminum in the engine it may go after the dead soft tin fire rings around coolant hole/combustion chamber or some other metalic part.
I have seen it too much so if you dont believe me , simply gife the coolant a look and a sniff it may be changed but if it smells funny then its not been changed (test strips for coolant can be bought from several companies)often enough or well enough.
And as for cleaning a system Zerex has a cleaner that you put in and drive the car for several hours then drain and flush the system (carefule as they also have one that is only supposed to be in for a few minutes give or take) the other one works great and you may even see some help for partially plugged heater cores and rads.
The big reason for ext life coolants was because of owners NOT servicing the old EG coolant and the silicates will fall out off suspension and create sludge.
hope this information from a working tech helps and if someone wants to tear into me because they think Im wrong email me at
Xanadu4024@aol.com
Lee Abel
ASE Master Automotive Technician