• From: NH
  • Registered: 2010-01-20
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Topic: Can't keep the Saab Cool

So, the saab has always had cooling issues. It gets warmer and warmer until we're really uncomfortable. I'm trying to wrap my head around what the best next changes should be.

Details on the current setup.
- 2008 Saab 9-5 2.3 turbo.
- Water pump was changed when the car was built and is known good. Thermostat also recent replacement and operates as expected (180deg model)
- Stock routing and hoses, the heater core is still plumbed in. 
- Radiator is new and a larger all aluminum aftermarket model.
- only other thing in the stack up is the intercooler which on the saab is the same footprint as the radiator.
- there is an undertray from the bumper to the radiator to keep air from ducking under.
- custom fan shroud that seals up against the radiator with two Spal 12in 1,328 cfm fans pulling through.
- The engine bay in the saab is stupidly tight, and the fans basically blow right onto the turbo and cat with no clear exhaust path. This picture shows both, the heat shield covers the exhaust manifold and turbo, and the cat is just to the right. https://photos.app.goo.gl/nsKgtsghLpcTwDqB7

What the car is doing.
When you start the car it will warm up and sit at thermostat temp just fine with the fans going. without the fans it will climb slowly like normal and then fall off to thermostat temps almost immediately when they kick on.
When you drive it on track, it will slowly heat up as you push it until it's north of 212 and we freak out. If you back off it will come down again, caution laps it drops to thermostat temp very quickly. if I throw it in neutral and coast half the front straight it will drop 5 degrees from that alone. Today I had the car at thompson for an HPDE and after 10 minutes of max pushing it would be up above 212. if I backed off my aggressiveness about 10%-15% it would stay around 206-210. Backing off means less time at WOT, coasting a bit more. Each session it would be back at thermostat temp by the time I was rolling through the pits to my spot.

Ideally I don't want temps over 205, even better I don't want them over 200. I'm trying to figure out the best changes to make to achieve this. My ideas in the order of attack that I think would be best.
1. Better seal up between the radiator and the support. It's not bad right now, but it is not perfect. Cheap and easy to improve.
2. Evaluate the front bumper and potentially open it up a little more to get more air in.
3. vent the hood. Small rectangle cut with a raised front lip to get some low pressure and allow the air an escape path. Will likely match with whatever "ducting" I can get down into the engine bay.
4. Do stupid things like install radiator misters that are overkill and do not sort the root cause of the issue but do satisfy my desire to over complicate.


I will get this out of the way. A little part of me fears a failing head gasket, but i'm not convinced. The coolant (water) is not changing colors (other than rust orange from the iron block), it does not smell, it's not sooty. I do not see bubbles in the expansion tank when it's running. when the head gasket was failing in my subaru it had issues with creeping temps at idle, even with the fans on, the saab does not have this problem. But this thought does sit at the back of my mind. I might grab one of the test kits just to be safe.

open to any ideas, thoughts, etc.

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  • From: Portlandia
  • Registered: 2014-08-08
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Re: Can't keep the Saab Cool

Are you running any oil cooling?

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  • From: Sachse,TX
  • Registered: 2017-10-21
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Re: Can't keep the Saab Cool

Are you certain all the air is out of the cooling system?

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  • From: WPB Fl.
  • Registered: 2010-10-27
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Re: Can't keep the Saab Cool

You describe a inadequate radiator, any chance the aftermarket unit is either under performing or plugged with orange rust?
also
Cut a hood hole.

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Re: Can't keep the Saab Cool

Is the lower (suction side) radiator hose collapsing?  Does it have a spring in it?

Is your gauge accurate?

Are you running lean?

  • From: NH
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Re: Can't keep the Saab Cool

Question answering

Yes, car has an oil cooler. Needs a bigger one. I have an rx7 unit to install.

All the air is out. It's filled and purged per the factory manual.

Aftermarket radiator is designed for this car and 48% larger than oem.

Hoses should be ok, but we bought new ones last week, good thought there. Gauge is the OBD reading, should be accurate. It says 179-181 when idling and we have a 180dag thermostat. Should not be lean, but I can install the wide band from the Daytona.

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  • From: Shippensburg, PA
  • Registered: 2010-11-18
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Re: Can't keep the Saab Cool

Do you know what temp the OE fan controllers turn on at?  I am guessing that this engine may be designed to run between 210-220.

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8 Reply by chaase (edited by chaase 2018-08-26 07:59 AM)

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Re: Can't keep the Saab Cool

racinrob wrote:

Do you know what temp the OE fan controllers turn on at?  I am guessing that this engine may be designed to run between 210-220.

Investigate this. Modern cars are meant to run at higher temperatures to help with emissions. In the Corvette world, if the car was modified, the next thing done is re-tune the car to turn the fans on sooner. Can you get a lower temperature thermostat? In the Saturn, we removed it completely.

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Re: Can't keep the Saab Cool

chaase wrote:
racinrob wrote:

Do you know what temp the OE fan controllers turn on at?  I am guessing that this engine may be designed to run between 210-220.

Investigate this. Modern cars are meant to run at higher temperatures to help with emissions. In the Corvette world, if the car was modified, the next thing done is re-tune the car to turn the fans on sooner. Can you get a lower temperature thermostat? In the Saturn, we removed it completely.


This was my thought as well. I recall 212-220 from my Automotive 101 class at the local JC 10 years ago or so.

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  • Registered: 2011-10-14
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Re: Can't keep the Saab Cool

I like this latter answer as it seems supported bysome Saab lore https://www.saabcentral.com/forums/show … p?t=128888.  That said, high temps always make us racers nervous but if the system is designed for 10 psi or greater, 212f seems in the operating range.

11 Reply by MDG

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Re: Can't keep the Saab Cool

Hi,
2 thoughts. First, you can rent a block tester from autozone, it will tell you if you have combustion gas in the cooling system (bad head gasket or other).

Second, it's your car and your comfort level but we back off at 245F. Our gauge only goes to 250F so we don't run past that. Our radiator cap would let us run to 262F before losing the water (22psi). 15 races so far on the same engine (Camry V6).

12 Reply by fleming95 (edited by fleming95 2018-08-26 11:17 AM)

  • Registered: 2009-06-10
  • Posts: 558

Re: Can't keep the Saab Cool

Engineering-type solution (for the self-affirmed overcomplicator):

- measure and log input coolant temperature to radiator
- measure and log output coolant temperature to radiator
- ditto for input and output air temperatures at radiator
- measure, or estimate, coolant flow
- calculate energy flow/unit time by [delta(temp)*(water mass)/unit time * (Cp)]
- infer air flow using steady-state cases, or otherwise measure air flow
- determine average and peak fuel flow, and duty cycle
- calculate total energy from fuel
- assume 70% energy is deposited in the coolant
- determine performance regions where heat input > heat rejection
- determine if cooling system is coolant flow or airflow limited in the exception cases

Lemons-solution

- More air.  Sawzall and speed holes.

(if you put a kitchen temperature gauge downstream of the radiator pre-and-post speedholing that'd be great though)

<edit>

Just looked at the picture - I was envisioning airflow space like in my transverse-engined cars - I have a tough time believing that air would ever make it out of that gap.  Is there a belly pan as well, so air has to find its way out the wheel wells?

</edit>
------------------------------------------------------------

The way you've described (with the quick time constants on cooldown when you stop pushing it, and a gradual rise when racing) sounds like the system is maxed out for heat rejection.

I'd guess that the cooling system is being fed 120% of its capacity at full tilt, and then the mass of the engine/transmission/etc. becomes the noticeable element in the 'radiator', with its thermal mass being ~20x that of the cooling system.

Any CHT or EGT data available?  The CHT would show the slower heat soak, and I expect that (and oil temperature) are the ones to watch with high coolant temperatures.

-Jeff

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Re: Can't keep the Saab Cool

TheEngineer wrote:

Question answering

Yes, car has an oil cooler. Needs a bigger one. I have an rx7 unit to install.

All the air is out. It's filled and purged per the factory manual.

Aftermarket radiator is designed for this car and 48% larger than oem.

Hoses should be ok, but we bought new ones last week, good thought there. Gauge is the OBD reading, should be accurate. It says 179-181 when idling and we have a 180dag thermostat. Should not be lean, but I can install the wide band from the Daytona.

Do you know how hot it actually gets when it climbs?

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  • From: Portlandia
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Re: Can't keep the Saab Cool

Lessons from the Jagvair: get the biggest aluminum radiator that will fit (or make fit), run a RX7 oil cooler, and make sure you have good air flow out of the engine compartment (or passenger seat, whichever applies).

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15 Reply by TheEngineer (edited by TheEngineer 2018-08-27 06:11 AM)

  • From: NH
  • Registered: 2010-01-20
  • Posts: 3,299

Re: Can't keep the Saab Cool

More question answering.

The fans are on a switch, we run them 100% of the time, so the OEM controller no longer applies.

i've never let it go above 217, I'm sure it would go higher if the opportunity was granted. I'm not comfortable with temps that high regardless. normal operating temps on the street are one thing, racing is another. Coolant temps climbing mean your oil temp is also climbing and the hotter the oil the worse it works. I would like to not see temps over 210.

there is no belly pan bast the radiator, the engine compartment is open to under the car.



Talking to eEurparts yesterday, their first suggestion was engine bay venting. They said venting the hood to their 9-3 race car made the biggest difference of anything.  So I think my plan of attack is as follows
1. Close up all gaps between the radiator and surround so all air must go through the radiator.
2. Vent the hood to allow more hot air to escape.
3. upgrade the OEM oil cooler to the RX7 model.
4. Install my wideband just for peace of mind
5. Start watching/recording a few more data points through OBD like EGT, Cat temp, what the car thinks the AFR is, etc.

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16 Reply by RSB

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Re: Can't keep the Saab Cool

We had the same problem at one time with our Audi. It would run at the thermostat temp (in our case, 90 Deg C) while idling but once on the track, temps would steadily climb to uncomfortably high levels. Turned out to be a partially plugged radiator. We swapped radiators and the problem went away (on-track temps between 90 and 100 Deg C).

Have you tried another (known good) radiator? Ours just suddenly "went bad" without any warning or damage inflicted to it.

Don't forget, the thermostat only controls the MINIMUM temperature of the system, not the maximum. If your cooling system is impaired, a lower temp thermostat will have no effect. The radiator is responsible for shedding system heat and and should be sized such that it can bring the temperature of the coolant down low enough so that the thermostat closes. If your radiator can't cool the system down to 180 Deg F, then it certainly can't cool it down to a lower value.

There is also a school of thought that says its bad to totally remove the thermostat, because that increases the flow rate of the coolant in the system, which reduces the amount of time the hot coolant spends in the radiator, further reducing the efficiency of the cooling system.

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  • From: NH
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Re: Can't keep the Saab Cool

Radiator is brand new. The symptoms have been the same with the old and new radiator.

I know you can't cool below the thermostat temp, We put the lower temp thermostat in to lower the min temp of the system.

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  • From: South of Chicago
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Re: Can't keep the Saab Cool

Nothing has been mentioned about the water pump. Is it OEM or aftermarket?  I've seen many water pumps sold that had a different design of the impeller than OEM and may or may not pump as well.  If you haven't looked at it then you should do so.

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Re: Can't keep the Saab Cool

Cut a hole in the hood behind the radiator and in front of the valve cover.  Roll the front edge up like a gurney flap.  Also you want the bumper opening smaller than the cross sectional area of the rad as well.  Use alum flashing and box the rad to the bumper if possible.  Removing that cat might lose some heat from the area keeping the turbo cooler as well.

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  • From: NH
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Re: Can't keep the Saab Cool

jimbbski wrote:

Nothing has been mentioned about the water pump. Is it OEM or aftermarket?  I've seen many water pumps sold that had a different design of the impeller than OEM and may or may not pump as well.  If you haven't looked at it then you should do so.

It's buried in the first post wall of text. Replaced after the first race. It wasn't OEM, but the design was the same as OEM.

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Re: Can't keep the Saab Cool

RSB wrote:

There is also a school of thought that says its bad to totally remove the thermostat, because that increases the flow rate of the coolant in the system, which reduces the amount of time the hot coolant spends in the radiator, further reducing the efficiency of the cooling system.

That is an old wive's tale.  Increased flow will lead to increased heat transfer.  Removing the tstat will increase the pressure downstream, though, possibly leading to hose failures, clamp failures,  or a failed radiator.

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Re: Can't keep the Saab Cool

NOPANTSDOUGIE wrote:

Cut a hole in the hood behind the radiator and in front of the valve cover.  Roll the front edge up like a gurney flap.  Also you want the bumper opening smaller than the cross sectional area of the rad as well.  Use alum flashing and box the rad to the bumper if possible.  Removing that cat might lose some heat from the area keeping the turbo cooler as well.

You don't want the bumper opening smaller than the radiator.  You want as large of an opening as possible.

23 Reply by bsure (edited by bsure 2018-08-27 10:57 AM)

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Re: Can't keep the Saab Cool

A lot of solid advice on here. You have to choose your methods and try them. You mentioned that you still had the cat in the car. Take that puppy out. It gets heat soaked and will be a tremendous source of underhood heat. They are not required and serve no good purpose in a race car. I
dont know if you still have the heater core in the car, but if you do hook it up and vent it outside, it will act like another small radiator.  Holes in the hood to pass air out as mentioned prevents air stacking and lets heat out. Good luck.,,
.

24 Reply by chaase (edited by chaase 2018-08-27 01:22 PM)

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Re: Can't keep the Saab Cool

rlchv70 wrote:
RSB wrote:

There is also a school of thought that says its bad to totally remove the thermostat, because that increases the flow rate of the coolant in the system, which reduces the amount of time the hot coolant spends in the radiator, further reducing the efficiency of the cooling system.

That is an old wive's tale.  Increased flow will lead to increased heat transfer.  Removing the tstat will increase the pressure downstream, though, possibly leading to hose failures, clamp failures,  or a failed radiator.

We haven't run them on any car so far. The thermostat can also fail and not open causing an overheat condition. We take it out and haven't had an issue but that is us. I guess its pick your poison 8-)

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  • From: Phoenix az
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Re: Can't keep the Saab Cool

it sounds like you are on the right path. but as mentioned by others lower t-stat or no thermostat. I blocked off the bypasses on my BMW and run no stat temps stay under 200. it gives you a lot more "cushion"  if your temps start at 160-170 that is more time before you see the 220.

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