The Cooling System Thread - C900

[SmaartAasSaabr]

My SPG came with Dex-Cool in the system. I think it's fine if you completely drain the engine and get every bit out. I have no clue whether or not the PO of this car did that or not, but it seems to be holding up.

Great writeup!

I hate DexCool. If Dex-Cool gets low in the system and mixes with air it starts making this terrible brown sludge out of the insides of the engine block. It probably isn't so much an issue with the C900 with the sealed reservoir but plenty GM cars have had issues with that and they have intake manifold gaskets rotting away all the time.

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I'd actually like to get a two position thermostat without the "heater cutout" function. It really is annoying to me with these old cars, because often you have something that is not working with the rad and so the thermostat devotes all its attention to the freaking rad. Like for example the fan isn't running, or the radiator is clogged, the coolant in the upper rad hose has frozen so no flow through the rad, or something like this, the heater core could save you and have no problems, but no, it cuts out the damn heater core and promptly the engine blows up It has happened to me so many times on so many different C900 and makes me swear so much

It seems like a design intended to keep using a undersized cooling system in an area that is too hot (desert etc) to try and make do with the small radiator (not really that small...) but doesn't take into account potential failure modes and the driver ability to mitigate them.

[SmaartAasSaabr]

Does this mean it is better to change coolant like one does brake fluid. In other words, let some drain out and fill the reservoir before the level goes down too much? Of course, that results in a lot of wasted fluid.

Nah, the system is relatively easy to bleed just with the screw on the thermostat and just burping it

the real problem arises when the engine is losing coolant for some reason (like rotted gaskets), and a lot of those GM's have the rad cap on the rad tank and the expansion tank is just with the hose, unpressurized, so the whole rad / heater core / engine gets clogged up with this terrible terrible sludge crap.

[euromobile900]

I'd actually like to get a two position thermostat without the "heater cutout" function.

First problem is, the "two position" stat has to have its bottom plate in the right spot so it doesn't permanently block off the heater, rather than permanently let it flow.

It really is annoying to me with these old cars, because often you have something that is not working with the rad and so the thermostat devotes all its attention to the freaking rad. Like for example the fan isn't running, or the radiator is clogged, the coolant in the upper rad hose has frozen so no flow through the rad, or something like this, the heater core could save you and have no problems, but no, it cuts out the damn heater core and promptly the engine blows up It has happened to me so many times on so many different C900 and makes me swear so much

As I said, don't think of it like it's devoting more coolant to the radiator. As we know, that is counterproductive--all it was designed to do is keep the heater core at the same temperature despite what the engine does, so that the passengers will have consistent heat dependent on the dial, not on the vicissitudes of the engine. Modern cars do this by pegging the heat in the center of the gauge with fans that have their own ECU (or fans that work via viscous coupling on RWD cars), so they don't need any thermostat for the heater core. With our single-speed fans, engine temp goes up and down, necessitating an extra part of the thermostat for heater control. If you had a two position stat, you might be swearing because you have to move the heater dial to "cold" to avoid burning your feet whenever you climb a hill or idle in traffic and the fan has to kick on. Our thermostat does this for us.

[mt.aero]

I hate DexCool. If Dex-Cool gets low in the system and mixes with air it starts making this terrible brown sludge out of the insides of the engine block. It probably isn't so much an issue with the C900 with the sealed reservoir but plenty GM cars have had issues with that and they have intake manifold gaskets rotting away all the time.

True, GM had issues with some cars and dexcool, but Saab was not one of them. If you are running dexcool in your newer saab, its a non-issue. Just dont mix.

[Dave T]

Nah, the system is relatively easy to bleed just with the screw on the thermostat and just burping it

the real problem arises when the engine is losing coolant for some reason (like rotted gaskets), and a lot of those GM's have the rad cap on the rad tank and the expansion tank is just with the hose, unpressurized, so the whole rad / heater core / engine gets clogged up with this terrible terrible sludge crap.

The classic 900 has a screw on the thermostat. I think the 9-3SS doesn't. Correct? I want to change the coolant on my car soon.

[mt.aero]

The classic 900 has a screw on the thermostat. I think the 9-3SS doesn't. Correct? I want to change the coolant on my car soon.

9-3 does not have the bleeder screw.

[SmaartAasSaabr]

First problem is, the "two position" stat has to have its bottom plate in the right spot so it doesn't permanently block off the heater, rather than permanently let it flow.


As I said, don't think of it like it's devoting more coolant to the radiator. As we know, that is counterproductive--all it was designed to do is keep the heater core at the same temperature despite what the engine does, so that the passengers will have consistent heat dependent on the dial, not on the vicissitudes of the engine. Modern cars do this by pegging the heat in the center of the gauge with fans that have their own ECU (or fans that work via viscous coupling on RWD cars), so they don't need any thermostat for the heater core. With our single-speed fans, engine temp goes up and down, necessitating an extra part of the thermostat for heater control. If you had a two position stat, you might be swearing because you have to move the heater dial to "cold" to avoid burning your feet whenever you climb a hill or idle in traffic and the fan has to kick on. Our thermostat does this for us.

It isn't quite that stable, if you look at the newer Saabs (NG900 and up) that always seem to have the gauge needle painted on, it is actually just lying, there is a "deadband" where anything from say 80 to 95 *C actually shows up as dead centre on the gauge where on our C900 it would wiggle a pretty decent amount

[euromobile900]

Do these newer SAABs have the weirdball 'stat as well? It's got to be stabler than our simple "on-off" fan system for controlling the upper temperature bound.

[SmaartAasSaabr]

I'm not sure, but I have doubts, they have moved to a more modern "air mixing" heat control where the heater is always in the loop. Except even newer ones like 9-5's have put back a heater valve that only closes when the A/C is turned on to improve the A/C performance. The 9-5 heater valve fails as often as the C900 heater valve but at least on a 9-5 you can throw it away. It is funny because we all talk of the "Saabness" disappearing on newer Saabs but every here and there some random Saab thing (usually an annoying thing that breaks too ) comes back!