Let me tell you a story about how bad 2EHA is.
When I bought my 2001 Subaru Legacy in 2007 with 67k miles, the radiator was already leaking. From what I could tell, it had the original factory coolant in it. I replaced the radiator and thermostat and while the thermostat was removed, I flushed the system with tap water from a garden hose. I then filled it with Prestone. I remember back then Prestone used to have those great mail-in rebates for like $7 per bottle and the bottles were like $9 for concentrate.
Anyway, since then I changed (drain and fill, no flush this time) the coolant again in 2013 when I replaced the head gaskets (which are well known problems on these engines), water pump and timing belt. The water pump looked great and the cooling system passages looked absolutely pristine (attached is a picture of where the upper radiator hose connects to the engine). I either used Prestone again or Supertech (which is a Dexclone made by Prestone, with identical ingredients to their pre-Corguard formula) mixed with tap water. I would buy Prestone when the mail-in rebate was available (unfortunately they haven't had one in years, or I've been missing it) or otherwise would buy Supertech for this car.
Just recently, the radiator from 2007 started leaking and when I replaced it, you guessed it, I did a drain/fill (no flush) with Supertech and tap water. The inside of the failed radiator and the cooling system passages were again all pristine and brand new looking. Before you try to say the coolant was at fault for this failed 13 year old plastic tank radiator, let me tell you that the only cooling system hoses I've changed on this car are the upper rad hose, lower rad hose and thermostat housing bypass hose. All the other hoses (there are at least 4 others) are original. The heater core is original and these cars have a full-time flow setup (no heater control valve), so hot coolant is always flowing through the heater core, all the time. There is a coolant crossover pipe on the top of these EJ25 engines and they have 2 o-rings where they connect to the engine. These o-rings are original and have never leaked. So for anyone who wants to blame the coolant for the 13 year old radiator failure, tell me how these other components could stand up to it and still be working fine after 19 years?
By the way, the car now has 138k miles. But don't be fooled, these are all city miles - nearly all stop & go driving, lots of idling, short trips, etc. The car is a daily driver and gets driven at least an hour every single day and it's been this way since I've owned it.
I've also used Prestone, Supertech and other Dexclones (like Napa Extended Life coolant, when on sale) in a 2005 Subaru Legacy, 2001 Forester, 2006 Civic, 2004 Acura TL, 2004 and 2005 Toyota Corolla and many others with the exact same results. Also, all of these are just drain and refills, no flush and mixed with tap water.
