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Modern coolants are designed with all sort of an additional requirements - alloy engines, long service intervals, environmental concerns - that may or may not apply to older engines. c900s were built in the days of "green coolant" - ethylene glycol and inorganic acids (aka IAT, like borate, nitrate, nitrite, phosphate, and silicate) for corrosion inhibitors. Newer coolants are still largely EG based, but use different materials for inhibitors. Some things like phosphate are discarded due to environmental concerns, some things like silicates discarded for component durability concerns, etc. Unless you have a specific need you're trying to address and you know how to do it, there is little incentive to switch to something else.

G48 is a hybrid organic acid (aka HOAT) based coolant, which means it uses primarily organic acids with a little silicate to do its job. HOAT coolants offer a longer service life than traditional IAT coolants, which is a nice benefit. But be aware that IAT and HOAT should not be mixed. If you don't know what's in the system, and you're going to put a HOAT coolant in, be SURE to thoroughly flush the system first.

Edit: It's maybe worth mentioning that truly traditional coolant - strict IAT green coolant - mostly doesn't exist anymore due to environmental impact. Lots of companies offer green coolant that can be mixed with old IAT, but 2019 "green coolant" is not the same as 1979 green coolant. They are probably compatible but chemically different. Prestone green coolant, for example, is widely acknowledged to be an OAT formula these days.
 

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You can defy it all you want, but every single coolant manufacturer explicitly recommends mixing before adding. If you do not, the heavier coolant will have a tendency to sink to the bottom of the radiator and stay there while lighter, thinner water travels over the top and may get "stuck" in pockets or cavities. These scenarios reduce the effectiveness of the system and possibly cause damage.
The reason for requiring you to mix beforehand, as far as I know, is that either by itself will freeze a lot sooner than the mix. So if you dump a 4 L jug of coolant into your Saab, and then dump in 3.5L of water, there's a good chance that your reservoir--which is the last thing to get mixed--will freeze in cold weather.

Coolant and water mix just fine. When I make up the mix, it's not like I have to put the result on a paint shaker for ten minutes to get it all mixed up. It pretty much mixes just with the pouring, never mind if it's pumped through a coolant system at pretty good speed.
 

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That's definitely one scenario, but the point is that pouring them in separately and then running the engine doesn't guarantee proper mixing in any sort of reasonable time frame. In some engines it might effectively never happen. Mix first, then pour. Every manufacturer is quite clear about that.
 

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Thanks for knowledge share jvnabra. That insight was what I was looking for ;)

... Unless you have a specific need you're trying to address and you know how to do it, there is little incentive to switch to something else.
But if the G48 is the reference that has a Saab certificate, why would I use anything different? If any reference would do, why would BASF and other suppliers bother with having a range of specifications? It seems that the easier route is to use what whe know to be up to Saab spec. I haven't found any other coolant suplier that clearly states that is made to Saab specs.

Full disclosure: I'm flushing the entire system
 

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The answer to that is complicated, and you probably need to put your conspiracy hat on.

"Old green coolant" was abandoned in Europe in the late '80s or early '90s since phosphates are quite toxic and Europe wanted that component gone. The rest of the world followed in the mid/late '90s. That environmental push is ultimately what killed conventional IAT based coolants.

At the same time, there are some side effects of using silicates in coolant - specifically, they can damage seals and even some moving parts with their abrasive nature. Removing silicates from coolant was driven by a desire for component durability.

Related, conventional IAT had a service life of about two years, and as manufacturers were pushing harder for longer service intervals, even "life of car" intervals, IAT had to evolve into something more durable. That's where HOATs and OATs come into play.

[Conspiracy]Manufacturers like nothing more than when you need to turn to them for parts, so they all came up with their own unique specifications that may or may not differ in some tiny way. So if you have a VW you need to buy G11 from VW instead of Glysantin G48 from BASF even though they're exactly the same thing. If you have a Ford you need to buy WSS-M97B44-D from a Ford dealership when in reality it's exactly the same thing as GM Dexcool. You can see this scenario play out over and over, and GM is clearly the king of this sort of branding.. "Dex" is now GM's brand for fluid, so we've got Dexcool coolant and Dexos oil, etc.[/conspiracy]

The problem with all these shenanigans is that in the pursuit of branding, environmental concerns, and service life there were some unintended consequences and side effects, which is why the universe went from one coolant that was used for decades to a dozen coolants that keep replacing each other. Maybe Dexcool/G34 melts some plastic, maybe G48 doesn't do well with a lot of aluminum, maybe G05 isn't quite as durable as we thought. So Mercedes specs G05 until they decide G48 is better, and Saab uses G48 until it decides Dexcool/G34 is better. Porsche uses G48 until it decides G40 is better.

AFAIK, Saab only spec'd "green coolant" for c900s. The G48 spec came in at the middle of the NG900 run and lasted until mid-2002 when they switched to G34/Dexcool. Who knows what the reasons were? I don't have enough info to say one is better than another in a c900, so I'd be hesitant to say, "Yeah make the change."

I can tell you that for a long time people SWORE by G05 in c900s. It was the coolant (google "saab c900 Mercedes coolant"). I've used that, G48, and even Dexcool in a c900 with no ill effects. Did I win anything? I dunno. But it seems the c900 is an old car with an old engine, and it's pretty happy no matter what you use.
 
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