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1991 900 turbo just rebuilt motor ,temp gauge sits just below the half way mark,let the motor run til fan kicked in ,temp gauge was more than 3/4 way on gauge,fan only ran for 5 sec,my question is what is the thermostat temp rating,and not sure on the temp rating on the thermo fan switch either,whats the match for these two things,do i go with a 89 degree thermostat,with a 82/77 degree c fan switch or hotter ?
 

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So, we can't tell you what thermostat you put in the motor, only you know that. The factory thermostat is 89C and the factory fan switch is 92C. Except in very unusual circumstances, these are the parts you want to run.
 

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So, we can't tell you what thermostat you put in the motor, only you know that. The factory thermostat is 89C and the factory fan switch is 92C. Except in very unusual circumstances, these are the parts you want to run.
JV; what would be the right circumstances for running 82C thermostat and Fan Switch?.....extremely hot weather?
 

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So, we can't tell you what thermostat you put in the motor, only you know that. The factory thermostat is 89C and the factory fan switch is 92C. Except in very unusual circumstances, these are the parts you want to run.
JV thanks for the info,this is my second engine redo on this Saab,and my 5th one,the last 2 Saabs,jjust rebuilt the top end of motor and new turbo on #4 ran great for about 6 mounths,threw a conecting rod threw the block and trany,got a seized motor and trans from my local Saab dealership for 300 with the rust free 91 body,never had headlight wipers till now,lol,long story short,I have a lot of spare parts,dont remember temp of thermostat,or the fan relay,i frankensteined this one 3 years ago,got sick,left it sit,now Im better,back on the Saab,It passed Emissions ,now just fine tuning.Thank You got lots more ?.
 

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JV; what would be the right circumstances for running 82C thermostat and Fan Switch?.....extremely hot weather?
I think that was Saab's approach, anyway. A lower temp thermostat and a lower temp fan switch to increase the safety margin for hot climates. AFAIK nothing in North America ever received those parts - they were reserved for the Middle East and maybe Australia. The stock parts will keep the engine running at 180F +/10F in perpetuity, which is a good place to be.
 

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Discussion Starter #7
What is the temp sensor in the middle of the top radiator hose to the thermostat housing,is that A/C related,and yes it is a great car to drive when it runs like a swiss watch.
 

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Discussion Starter #8
I had two temp sensors for the block,thinking both r shot,pull the connection off ,ground it ,turn on ignition they both make gauge got to top,next is thermostat I think stuck open
 

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There are four "temp sensors" -

NTC sensor in intake manifold between #2 and #3 runner, this is the ECT sensor for fuel injection

Thermistor at the front of the head by the thermostat, this is for the gauge

Thermoswitch in radiator above the lower radiator hose, this is the radiator fan switch

Thermoswitch in the upper radiator hose, this disables the AC compressor when the temperature is too high
 

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I think that was Saab's approach, anyway. A lower temp thermostat and a lower temp fan switch to increase the safety margin for hot climates. AFAIK nothing in North America ever received those parts - they were reserved for the Middle East and maybe Australia. The stock parts will keep the engine running at 180F +/10F in perpetuity, which is a good place to be.
Ok. I ask because I decided to change my temp fan switch to a 82c instead of changing my 82c thermostat back to an 89c - This because i live in southern FL where ambient temps average around 35c (95f) most of the year with black top road temps in the heat of the day much higher than that.
I'll see how it goes this summer. Sorry to hi-jack the thread and thanks for the info:)
 

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Read this antique post before you make that mistake.
 

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Interesting thread indeed. I think that's the longest post I've seen from you, Jim:).
I will go back to stock. Thank you for digging up this old thread.
 

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That's a great post... one thing is particular is this note:

Some say the number of heating and cooling cycles is a big factor.
This has DEFINITELY been borne out as true, and you can see evidence of that in modern cars. Back in the '80s you'd find cars with 192F thermostats and 230F fan switches pretty commonly. Lots of people think it was manufacturers being cheap and not wanting to fix cheap electric fans under warranty by running them too much. Not sure if that's true or not, but whatever. Point is, that's a very wide range of temperature that the engine is constantly cycling between, which is hard on everything.

Modern engines typically operate in a very narrow range of temperature - usually +/-10F or so - which reduces maintenance requirements and provides more consistent operating characteristics. Lessons about heat cycling were learned.

Most European brands were onto this pretty early on. Certainly Saab was, and the 900 stays within a 10F operating range very consistently.

I think virtually everybody underestimates the importance of just staying on top of coolant... failure to do that will lead to the system turning corrosive, damaging the head, gasket, and clogging the radiator. Every c900 I've done a head gasket on show signs of abuse here. Pitted heads, rust, chewed up head gasket.

If you maintain your cooling system you will get excellent life & performance from the system. I copied the c900's cooling system design when I redid my XR4Ti, and the result has been improved power, improved fuel economy, and far more consistent operation. Best thing I ever did!
 

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Discussion Starter #16
There are four "temp sensors" -

NTC sensor in intake manifold between #2 and #3 runner, this is the ECT sensor for fuel injection

Thermistor at the front of the head by the thermostat, this is for the gauge

Thermoswitch in radiator above the lower radiator hose, this is the radiator fan switch

Thermoswitch in the upper radiator hose, this disables the AC compressor when the temperature is too high
Thank you very much,the true test will be when it gets 90 here
 

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Discussion Starter #17
That's a great post... one thing is particular is this note:



This has DEFINITELY been borne out as true, and you can see evidence of that in modern cars. Back in the '80s you'd find cars with 192F thermostats and 230F fan switches pretty commonly. Lots of people think it was manufacturers being cheap and not wanting to fix cheap electric fans under warranty by running them too much. Not sure if that's true or not, but whatever. Point is, that's a very wide range of temperature that the engine is constantly cycling between, which is hard on everything.

Modern engines typically operate in a very narrow range of temperature - usually +/-10F or so - which reduces maintenance requirements and provides more consistent operating characteristics. Lessons about heat cycling were learned.

Most European brands were onto this pretty early on. Certainly Saab was, and the 900 stays within a 10F operating range very consistently.

I think virtually everybody underestimates the importance of just staying on top of coolant... failure to do that will lead to the system turning corrosive, damaging the head, gasket, and clogging the radiator. Every c900 I've done a head gasket on show signs of abuse here. Pitted heads, rust, chewed up head gasket.

If you maintain your cooling system you will get excellent life & performance from the system. I copied the c900's cooling system design when I redid my XR4Ti, and the result has been improved power, improved fuel economy, and far more consistent operation. Best thing I ever did!
What Coolant is the top Dog,orange green,red ?
 
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