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  1. #1
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    '90 900 LPT with a flat-nose conversion
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    The Cooling System Thread - C900

    This thread will be all about the c900 cooling system, from what coolant to use to thermostat choice to water pump quality to block drain replacement to radiator hype.

    Difficulty: Most cooling system work is a solid 2/5.

    Tools Required:
    -13mm wrench or breaker bar for the block drain
    -2x 11mm wrenches for the coolant bleeder
    -8mm wrench or socket for the hose clamps. Don't use a screwdriver unless it's all you have. 1/4" drive extensions, swivels, and U-joints are useful for tightening some hose clamps around the water pump area
    -Razor blade for cleaning gasket surfaces if you are changing your water pump
    -Big huge adjustable wrench for the coolant temperature switches, both for A/C cutoff and fan cut-in (I don't remember what size these are, but they aren't in hard).

    Parts Required:
    -Whatever you decide to replace!

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  2. #2
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    '90 900 LPT with a flat-nose conversion
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    Arrow Tom Townsend's Thermostat Snafu

    One of the first sites we all get directed toward as new c900 owners is Tom Townsend's SAAB advice site. On this site, he does not hesitate to insist that all c900s would have fewer cooling system problems (and even fewer head gasket failures) with 82º thermostats.

    He gives several reasons for this, including that you'll have more time to respond to a potential overheat situation. The only argument of his that really makes any sense at all is the argument that the 82º thermostat coupled with an 82º fan thermoswitch will keep the temperature within a very narrow range. A narrower operating range means the head and block will be undergoing narrower expansion/contraction cycles, and because they are aluminum and steel, different expansion/contraction ratios will be less likely to cause head gasket failure.

    I say this is bunk.

    First of all, we must think about how our cooling systems work.
    The thermostat in our cars does two things. First and foremost, it sets the lower bound for the temperature range. When the coolant is cold, it remains cold, so the engine will only have to warm up the coolant in the block. When the coolant starts getting warm, it opens, allowing warm coolant to hit the radiator and displace cold coolant from the radiator back up into the engine. The second thing the thermostat does is block the inlet to the heater core when the car overheats. This "third position" forces all hot coolant to travel to the more-efficient radiator, and is why you should use a genuine SAAB thermostat, not an aftermarket one, which will likely only have two positions and may block off your heater circuit permanently.
    The fan switch does one thing: form the upper bound for the temperature range. It's located at the upper left corner of the radiator, the place where hot coolant will go if it's not getting cooled off enough by the radiator. Thusly, it is kind of "testing" radiator function. When the radiator hasn't cooled the coolant enough, it turns on the fans. This cools the coolant very well, desaturating the radiator in the process, and so the cold coolant shuts off the switch.
    The important thing to remember is that, unless it's stuck shut (easy to tell), the thermostat does nothing for overheating!

    Having a colder engine will only lead to inefficient operation. A warmer engine is always more efficient, hence SAAB's decision to opt for 89º stats in the majority of production cars. The 7º difference between 82º and 89º will buy you an extra 3 minutes or so in an overheat situation, so it's not like running colder will prevent you from overheating.

    Narrowing the temperature range will also cause your cooling fans to run near constantly, a complaint I've heard time and again from people who've switched to the 82/82 'stat/thermoswitch combo. The temperature range is already only 3º, with the stock setup for most c900s: an 89º stat and a 92º thermoswitch. Narrow it much more, and the thermostat and fans are going to "fight" each other.

    The engineers at SAAB were also very smart, and would have likely thought of a problem like this and equipped all the cars with narrow-range cooling systems if it were beneficial. With the multiple-speed fan operation of the 9000, or the variable speed cooling fan operation on most RWD cars (controlled by a viscous coupling and a special fluid that thickens as it is heated), it is possible to keep the coolant temperature within a narrow range, or even "pin" the temperature gauge smack in the middle.

    Our cars don't have that, so I've elected to be content with the 3º fluctuation in temperature and stop worrying. I would like the fluctuation to be smaller, and I think it could be done, perhaps with the 89º stat and a 91º or 90º thermoswitch (certainly available, for other cars, but would require some research to find one that fits). Another thing that would be really nice is an add-on, standalone cooling fan ECU, like one from a Toyota, that could drive our fans and pin our temperature smack in the middle. But again, this would require money and time and knowledge of Toyotas to develop.

    The problem isn't big, and the solution is difficult, expensive, and hasn't even been done yet.

    Aren't our thermostats special?
    Townsend mentions how our cars are equipped with a special "three position" thermostat. He says this means that our thermostats can shut off the heater in case of an Overheat Situation, because this "allows coolant to flow directly to the most efficient heat exchanger, the radiator." He says we all need to buy OEM thermostats, because otherwise we won't have this important safety feature.

    He's sorta right. Normal cars' thermostats have nothing to do with the heater. Their heaters are only controlled by the heater valve. This means that the heater will be warmer or colder depending on how warm the engine is. To warm up, normal cars have an internal bypass inside the engine block or an external radiator-bypass hose to allow coolant to recirculate through the engine when it's cold. As a normal car's thermostat opens, it diverts coolant from the bypass into the radiator. The heater circuit is untouched. It looks like this:
    Name:  coolingsys.jpg
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    But our engines are different. They have no internal bypass to allow the coolant to warm up. Instead, when the engine is fully cold, the thermostat allows full flow of coolant only to the heater core. The heater valve never closes. It just diverts flow through an internal bypass inside the heater. So, our heater functions like a normal car's bypass circuit for warmup. As the engine warms up, coolant flow is diverted through the radiator more and more, and less through the heater. This means that our heaters stay at the same temperature, regardless of what the coolant temperature is (unless it's dead cold)! That's why our heaters warm up so fast! And, the thermostat can still warm up the coolant quickly by forcing it through the heater, whether the valve is set to warm or cold. It looks like this:
    Name:  coolingsys.jpg
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    The problem is, some aftermarket thermostat manufacturers haven't really caught on to how our cars work. They put a normal thermostat in, which will only control flow to the radiator, and not to the heater/bypass circuit. This means (depending on how it's built) that you might get full flow to the heater/bypass, or you might get none. And it can't change, so your cooling system will either be functioning inefficiently, or you'll have no heat, or somewhere in between.

    The Bottom Line
    Get the proper thermostat for your car (probably an 89º). Match it with the proper thermo fan switch (probably a 92º). And buy an OEM Stat, or you may be stuck without heat, or with too much heat.

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    Last edited by euromobile900; 12 March 2011 at 06:07.
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  3. #3
    Sam Carlson
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    '90 900 LPT with a flat-nose conversion
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    Mercedes Coolant: Legend, Myth, and Science

    The other thing Townsend recommends is Mercedes coolant. He tells the story that he was in the Merc dealer, picking up parts, and saw coolant on the wall that was cheap, so he bought some. He then noticed a big drop in the amount of corrosion in his customers' engine blocks, water pumps, and head gaskets.

    It seems that, in this case, unlike in the case of the 82º stat, he was doing good science, and was not committing the "fallacy of the lonely fact". He started using Merc coolant all the time, and everybody lived happily ever after.

    Sorta.

    In recent years, Merc coolant has become hard to find and expensive, especially on the internet, because shipping gallon jugs of coolant is a pain. Most Americans don't have access to a Benz dealer nearby. So, when I was living in the sticks, I decided to see if there was an alternative.

    First, I tracked down the elusive formula of Merc coolant in Townsend's specified era, "the mid '80s coolant shortage". Its corrosion protection was a special chemical formulated by BASF in Germany, called Glysantin. Its formula differed from the Glysantin of today, how we do not know, but the "miracle coolant" that Townsend first discovered may not even exist anymore.

    However, hope is not lost. The various generations of Merc coolant all meet the same spec, which is now known as G-05, and which requires a certain kind of corrosion protection, called Hybrid Organic Acid Technology (HOAT). Merc's G-05 coolant got put in everything the Daimler Benz corporation bought, including Chrysler, when Daimler bought them. So, because of Benz's acquisitions and tech-sharing, now the Glysantin G-05 HOAT coolant spec is prolific, and you can get basically the same thing as current Merc coolant from any auto parts store. Just ask for G-05 coolant, and if they are worth their salt they'll have it on hand from a brand like Zerex or Mopar!

    Helpful hints on what is G-05:
    -Zerex G-05
    -Motorcraft Premium Gold
    -MOPAR coolant
    -Mercedes coolant

    The G-05 coolant is fine stuff, costs a bit more but nothing a low-volume DIYer cannot afford, and may provide substantial benefits. I say why not use it! It mixes right with your green coolant too, so if you don't get it all out, never fear.

    Now, you might ask, what about Dex-Cool, the other "miracle coolant"? Well--when you mix it with ordinary coolant or G-05 coolant, it will form sludge. I suggest keeping Dex-Cool far away from your engine unless you have a hankering to use it after a rebuild.

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    Last edited by euromobile900; 28 October 2010 at 22:50.
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  4. #4
    Sam Carlson
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    '90 900 LPT with a flat-nose conversion
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    Radiators: Aluminum, Copper, and whether you need one

    How to tell if you need a new Radiator
    If your radiator leaks and is very old, you are likely better off getting a new one. It's an easy repair, to put one in, and the price of a new one and DIY-ing will likely be less than the price of getting a shop to repair your old one.

    Often your radiator can look like this:
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    Just a little bit green, but perfect fins,

    But when you touch it, it will look like this:
    Name:  IMG_3086.jpg
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    Mine disintegrated when I touched it. Obviously if it is like mine, you need to replace. I once met a c900 with a radiator that had lost all its fins, retaining only the tubes going across.

    If your cooling system is not working well, and you're confident in your hoses, stat, and fan switch, and it seems to be an upper-bound-of-temp-range problem, then I'd consider radiator replacement. Removal and flushing can sometimes clear up a radiator that's plugged from the inside, but oftentimes will not remove hard water deposits and "solder-bloom" (deposits that form on high-lead solder joints inside the radiator).

    Aluminum vs. Copper
    This subject is so hotly debated, I don't know what's best anymore. It used to be that aluminum had a reputation as junk, but companies like Nissens are turning that around, manufacturing well-made aluminum radiators as original equipment in many cars and trucks. The trouble is, well-made aluminum radiators are so new, nobody has any real data yet on how they corrode compared to copper ones, which have often been in our cars for years upon years. Without question, uncoated aluminum and copper both corrode. Aluminum and copper radiators both have to be coated so they don't corrode. All coatings fail eventually, like mine did:
    Name:  IMG_3089.jpg
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    Without question, copper is easier to fix than aluminum, because copper can be soldered and aluminum radiators come with plastic endtanks, sealed with rubber gaskets, which require a special crimping tool to re-seal. Without question, aluminum can give you more cooling power per weight and per surface area. Other than that, it's up in the air.

    Near as I can tell, Nissens powder-coats their aluminum radiator. The copper radiator you can buy from the Saabsite is painted black. Anything you can buy from a reputable supplier today probably painted way better than your original SAAB one. If you get your original re-cored, you should make sure they paint it!! Bottom line: I'd buy based on the quality of the corrosion coating and the reputability of the manufacturer, rather than the material the radiator is made out of.

    Turbo vs. Non-Turbo
    SAAB c900 came from the factory with two different radiators depending on model: turbos got a thinner one and non-turbos got a thicker one, because of the turbo's increased load on the cooling system. I think this extended only to cars with water-cooled turbos, but I could be wrong. However, new aftermarket radiators will all be made to the Turbo spec, which is more effective at cooling. If you're sourcing one from a scrapyard, better stay away from the N/A radiator, because if it's original you could be downgrading. But when buying new, do not fear.

    Finally, what I did: I replaced my fubar'd copper radiator with a Nissens radiator. It's been in service for a year and a half, and it's held up fine, and cooled me well through 106ºF desert days.

    To replace radiator:
    Drain the radiator. I recommend not using the radiator petcock, as this is easy to break on a 20-year-old car. Instead, pull the lower hose off and drain the coolant from there. If you don't want to change your coolant at the same time (I recommend a full coolant change after changing radiators), pull the lower hose off, and quickly raise it up and tuck it under something or zip-tie it to the intake so it's up high and can't leak. Remove the upper hose and do the same thing. Unplug both fans at their two-pin connectors. Remove the wires from the fan thermoswitch, on the upper left corner of the radiator. Unscrew the two 10mm bolts at the top. Undo the 10mm bolt that holds your coil on, and set the coil above the radiator, on the radiator-support.

    At this point, you should be able to tilt the radiator back. If you can tilt it back far enough, it should be possible to slide it directly up and out of the engine bay. If not, you'll have to do what I did and remove one or both of the fans. I got mine out by removing the right side fan only, and once I got it out without removing any fans (somehow!) With a Turbo, you'll have piping to deal with as well. Just remove what you need, until you can see that the front of the radiator clears the support. Then pull up! The radiator is held at the bottom by two pins that stick downward into a set of rubber-lined sockets in the radiator support. They should come right out.

    And, as they say, installation is the reverse of removal. Often installation is easier, even if you mount both fans on beforehand, somehow. Don't forget to put the fan thermoswitch on your new radiator!

    If you need to remove the radiator for easier access to something (primary drive?), you can do it without disconnecting any hoses (still disconnect fan thermoswitch wires and unplug the fans), and just set it on top of the engine.

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    Last edited by euromobile900; 11 July 2011 at 04:35.
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  5. #5
    Jose Luis
    Saab Addict jlrSAAB's Avatar
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    Quote Originally Posted by euromobile900 View Post
    This thread will be all about the c900 cooling system,

    from what coolant to use

    I have never flushed the coolant. only refilled it.

    I use the long life coolant (no water mixed) is already prepared to refill the tank as it

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  6. #6
    Sam Carlson
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    That looks like Dex-Cool to me. Fine for newer SAABs (I think?) but I'd not risk putting it into the c900's cooling system, unless you're pouring it into a dry engine right after overhauling, due to mixing concerns.

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  7. #7
    Neil Richardson
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    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!

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  8. #8
    Sam Carlson
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    Quote Originally Posted by Saabhat93 View Post
    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!
    Thanks! I tend to agree with you about Dex-Cool. I just don't think it's worth the flushing and draining to switch! Even Napa has stopped carrying the stuff in pure form, which makes me think it's on its way out. But if you've got it, might as well roll with it. For practicality's and worrywart's sake, I think it's best to go with what you have if it's been working, unless you're upgrading from Green to G-05.

    Once I did mix Dex-Cool with some G-05 just to see what would happen. It formed a precipitate, just like in chemistry lab

    I just edited my post about thermostats to include some information I garnered about the mythical "three position" stat. See above for fantastic Townsend-bashing!

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    Last edited by euromobile900; 12 March 2011 at 06:30.
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  9. #9
    Edward G
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    so what do you recommend I live in Australia which gets 40 celcius days during summer,but doesn't get much below 0degrees celcius during winter, should I run a 82 thermostat and 92 fan? or 82 thermostat and 82 fan... all the saab guys in Aus say 82 and 82... but I don't think this is nearly as important as having a clean radiator.. On hot days my thermostat opens regularly to keep temperature at 2/3 gauge, in winter on normal driving gauge never goes over 1/3... My friend has a SPG whos gauge never goes over 1/3 - new radiator?

    Also Is the 82 degree thermostat on eeuroparts a 3 stage one, it is not OEM, and is the only thermostat offered there which I think is a bit strange... where would you get an 89 degree or 92 degree?

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  10. #10
    Sam Carlson
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    Quote Originally Posted by s900t8v View Post
    so what do you recommend I live in Australia which gets 40 celcius days during summer,but doesn't get much below 0degrees celcius during winter, should I run a 82 thermostat and 92 fan? or 82 thermostat and 82 fan... all the saab guys in Aus say 82 and 82... but I don't think this is nearly as important as having a clean radiator..
    I, too, find that a new or clean radiator helps immensely. I lived in a desert climate (high temperatures sometimes got to 105ºF) one summer. I bought a new aluminum radiator, 89 stat, and 92 fan switch, and my car _never_ overheated, climbing hills or in traffic.

    On hot days my thermostat opens regularly to keep temperature at 2/3 gauge, in winter on normal driving gauge never goes over 1/3... My friend has a SPG whos gauge never goes over 1/3 - new radiator?
    If the temperature gauge is not rising, it is possibly due to a stuck thermostat, or a thermostat and fan switch combo that is too cold. Remember, the thermostat sets the bottom of the operating temp range and the fan switch sets the top. Your fan switch or speed of driving is what's keeping the temperature at 2/3. A properly-functioning thermostat should be wide-open on a hot day like that, and not shut until you turn the car off. The temperature will be totally controlled by the fan switch after warmup. Likewise, on a cold day, the thermostat will function on its own, closing to raise the temperature and opening to lower it, and the fan switch plays no part.

    Also Is the 82 degree thermostat on eeuroparts a 3 stage one, it is not OEM, and is the only thermostat offered there which I think is a bit strange... where would you get an 89 degree or 92 degree?
    eEuroparts has them all, from OEM/OES and aftermarket. Unfortunately, I do not know how to tell a 3-position stat by looking at it, so I can't tell you the answer to that question. Having said that, I do know that the Saabsite is affiliated with Tom Townsend, so I would imagine they'd only sell the three-position ones. Don't take my word for that! Write them an e-mail and ask!

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