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Discussion Starter · #1 ·
I'm thinking this number is a little low, considering I'm driving under 75MPH the whole time. Any inputs on what the problem might be? my car has little over 83,000 miles, (semi) new O2 Sensor, new plugs, sythetic oil.
 

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That is more than a little low, it is a lot low. We had a thread about that recently.

http://www.saabcentral.com/forums/showthread.php?p=1147346#post1147346

If you have not already done it, I would test the fuel consumption starting abut 5 minutes after the engine warms up (meaning temp gauge at 9 o'clock), and at steady hwy speed. Reset the SID, drive for about 10-12 miles, and see what you get.

If the engine is in otherwise good shape, my favorite suspect is the coolant thermostat. Some strong injector cleaner might not hurt either (from a part store, not a gas station, something like Techron Concentrate or similar).

A bad thermostat can make the engine run too cold, and below the temperature needed for the ECU to control the air/fuel mix correctly, and dirty fuel injectors can have a poor spray pattern and lead to partial fuel combustion.

Injectors will lower the mpg year-round, the thermostat will have a bigger effect in winter.
 

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PMI said:
If the engine is in otherwise good shape, my favorite suspect is the coolant thermostat.
Good call on this one PMI. While it may not be his problem I always look here first. I would also recommend cleaning the Mass Airflow Sensor (MAF) as well. I have had both of these components cause poor MPG on Fords in the past. The thermostat stuck open on a 2.4L Ranger and dropped the mileage from 28mpg to 18mpg. A dead ladybug carcass on a MAF took a 4.0L Explorer from 22MPG to 9mpg.
 

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Discussion Starter · #4 ·
the thermostat is def a possibility. Is it linked to the heating capabilities? cause the heat is very very low and I'm feeling very cold this winter driving in my saab.
 

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The thermostat regulates the amount of coolant flow through the engine. If it sticks open, more coolant circulates (in winter, that means more frigid coolant) and the engine or the coolant inside the engine never heats up to normal engine temperature. Neither does the heater core, which is fed from the engine through a separate set of hoses.

If the heater core never gets warm, neither will the air from the vents.

My original thermostat failed well before 80K miles.
 

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Discussion Starter · #7 · (Edited)
it's funny cause when my car is idle, the heat is there and I feel the heater core doing it's job. But when I get going on the highway, the heat disappears and it feels like the heater core isn't doing it's job. However, after I get off the highway and let the car idle for 2 min, the heat comes back. so the only time the heater core is not doing it's job is when it's on the highway. Strange :confused: How difficult is it to replace the thermostat?
 

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goorackerelite said:
it's funny cause when my car is idle, the heat is there and I feel the heater core doing it's job. But when I get going on the highway, the heat disappears ...
Classic symptom of a bad thermostat.

It is not the heater core not doing its job, the coolant inside the heater core is too cold on the hwy.

On the hwy, freezing air flows over the radiator, and the radiator gets very cold. So does the coolant. Normally the thermostat starts to close, and reduces the flow of coolant through the engine, so the engine and the heater core stay at the correct temperature.

When the thermostat fails and sticks open, nothing keeps the frigid coolant out of the engine and out of the heater core. The engine temperature and the heater core temperature drop. You get very poor gas mileage, and little or no heat in the car.

At idle, there is much less air circulation (even with the fan). The coolant temperature rises, and the heater core gets warm again.
 

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I'm getting about 22-23 mpg on my 9-3 auto with an MBC+A. The little woman is the driver... Is there any indication the thermostat is bad as the gauge sits barely about 1/2 and it blows hot air.
 

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thermostat test

A quick check to make sure that it is a bad thermostat: Put a piece of cardboard in front of the radiator (or the A/C condenser, in most cases). Take your car out for a ride on the highway and see if the temperature stays up. Keep a close eye on the gauge, though, and pull over and remove the obstruction if there is even a hint of the temperature going too high.

If it's cold enough outside, you can safely block the entire radiator without overheating. Note that this is only a temporary "test" fix. If you have a warm spell, you can easily overheat your engine if you leave the cardboard in place. However, you might notice many heavy trucks use a vinyl cover over the grille for just this purpose. It's called a "winter front" and used to be quite common on vehicles back in the old days.

The thermostat on my Packard opens and closes louvers in the grille; it does not block the flow of water at all, only the flow of air. This was pretty common practice in the 1930's, but modern thermostats (when the are working) are far better at keeping an engine running in the proper temperature range. Changing is not too difficult. Good luck.
 
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