Radiator flush and fill. Can I replace with ANY antifreeze?

If so, what should I put in my 1999 Denali?

As a GM product it is supposed to use dex-cool but I have never heard good things about it. Of course the other option offered is refill with Generic Green ® antifreeze which doesn’t mix with Dex-Cool because nothing mixes with dex-cool. If I can replace with generic then why can’t I replace with HOAT (orange) anti-freeze?

So should I (do I have to) stay with Dex-Cool? If not, what anti-freeze should I replace it with?

use the same stuff as what the factory put in. the problem with Dex-cool in the past was a material incompatibility with gaskets on certain engines. if it was going to be a problem for you, on a 1999MY vehicle you would have encountered it a long time ago.

you can intermix antifreeze types, but if you put some of the green stuff in there you shorten the change interval to ~ 30,000 miles.

Mixing different types of anti-freeze is not a good idea.

GM isn’t alone with its Dexcool concoction. Other manufacturers use their own creations to better prevent cooling systems from rust and to extend the life of the coolants. They aren’t your father’s anti-freeze any more.

Follow what the owner’s manual says.

I’ve always kept the same as the owners manual suggested, for all fluids. They are recommended for a reason.

If it’s been using Dex-cool since 1999, why change now?

Why would you want to change? It seems far safer to stay with Dex-cool and no potential benefit gained from trying to use a different type, unless Dex cool is uber expensive. The best case you can hope for by switching is no problems which you have already with Dex-cool?

It’s best not to use traditional green (IAT) antifreeze in your vehicle, or any vehicle that didn’t use it as the factory fill. It can be used if the system is thoroughly flushed, but it’s the poorest choice of the types of antifreeze.

This chart shows which basic type (IAT in green, OAT=Dex-Cool in orange, or HOAT in yellow) is appropriate for various makes.

Dec-Cool works great if two important details are attended to:
> Make sure the antifreeze/water mix is ABSOLUTELY AT LEAST 50% antifreeze. A 49/51 mix can cause problems. Seriously.
> Make sure there’s no air in the system – properly bled, pressure cap works properly, sufficient liquid in the overflow jar.

HOAT antifreeze will mix with IAT or OAT without causing problems. However, some of the additives (e.g. silicates and phosphates) may not be what the car manufacturer calls for. Theoretically this could cause problems; in the real world I haven’t seen any, though some years ago I did read a horror story in an automotive trade journal about one case.

The safest bet is to use Dex-Cool paying attention to the cautions I mentioned above. If you want to use HOAT, it’s unlikely you’ll have a problem but no one wants to guarantee that you won’t.

Depends on your particular vehicle. I have a 2005 Dodge,which specifies HOAT coolant meeting the MS9769 spec (the Zerex G-05 was factory fill apparently).

However, the Prestone Dex-Cool meets the MS9769 spec even though it isn’t HOAT. I’ve had it in my radiator for 4 years now, and no problems whatsoever.

Forgot to mention:

Many of the earlier problems with Dex-Cool were because service personnel were not advised as to how important the antifreeze/water ratio and exclusion of air from the system were. They were understandably not fastidious about something that hadn’t mattered before (with IAT). The result was a lot of corrosion that could have been avoided.