changing coolant on 2007 2500HD

#1Flyboy wrote:
. . .Silica fallout is usually found in OLD antifreeze( REALLY OLD!!! ) & usually in Diesel engines IF not keeping up with their nitrate levels/ coolant filters. . . NOT an issue with todays coolants as they are formulated (When is last time in last 10 years anyone saw silicate fallout?). . .I worked a successful automotive cooling system shop (33 years) & yes, actually purchased FULL trailer loads (20 pallets) of coolant at a time. . .Only took a few classes on coolants & such but had 43 years in cooling systems industry addressing & solving problems with cooling systems. . .Also talked to several AC Delco guys(at trade shows) about their Dex-Cool problems & every one of them had a different answer. . .By the way your link did not work.. . .YMMV. . .

Well, silica fallout still happens today and forms goo. Here's what happen when you take the coolant from a 2012 chrysler vehicle using a HOAT and mix it with 5% or more of the new OAT (AKA Grapejuice) that chrysler is using in a 2013 vehicle: http://starparts.chrysler.com/newsletters/newsletter_Oct_2012.pdf It's a PDF, so you need to have a PDF viewer to see this as with my last link. Seems to work fine for me anyways. On page 4 of the print, you can see the results of the mixing. This alone disproves that all coolants are compatible with one another.

Some coolants do have wide compatibility, but when you mix coolants, you are always diluting their additive package and I am not a chemist, so I can't tell you what would happen if you mix brand x with brand y. That's why I personally believe in following the manufacturer specs.

Also, Japanese auto makers tend to use a phosphated anti-freeze, primarily because of the intense use in aluminum and such, along with the quick development of that "film" that protects and coats all the parts quicker than a normal OAT. Then Daimler still uses a Silicated anti-freeze. Mix that Silicated with certain OAT anti-freeze and you can run into more of the gelling issues. Another reason why I'm really careful about anti-freeze selection.

However to the OP, I reviewed my coolant notes while at work today. If you did have a full flush in the system and have less than 5% of the old anti-freeze mixed with the new antifreeze and what they used is a universal coolant. You may be able to get away with it. However, you'd still want to flush fairly early compared to the normal 5yr/150k miles that I believe GM recommends for Coolant replacement.

Really the issue is mixing of coolants. However, even though people call it "Deathcool", I think it earned that name due to its early implementation and not understanding the full properties of OAT coolants, especially the 2-eha that's in DEXCOOL. That tends to soften certain seals and types of plastics overtime. Personally, I like that Chrysler's new OAT doesn't use 2-EHA so I'm hoping I don't have the issue with my motor in the future but I will still watch it.

If you're bored, here's a good article on Coolant in general, it goes through why certain packages are in certain coolants and such and may open your eyes to who uses what (and yes, this is a professional rag) (although it's titled to talk about Chrysler's coolant switch): SAE Coolant Article