OK to drive w/ thermostat stuck open? (mildly urgent) [Archive] - SaabCentral Forums

: OK to drive w/ thermostat stuck open? (mildly urgent)

Black Beauty
13th March 2005, 01:50 AM
I am visiting my mother in Omaha this weekend, who is fighting pancreatic cancer. I am supposed to drive back to Minneapolis tomorrow, Sunday (actually leaving in about 12 hours).

My 2000 9-5 Aero has symptoms of a stuck-open thermostat. (Temp gauge to zero; CEL; 10 miles of highway driving results in engine which is warm, but still cool enough to touch; little to no hot air in cabin; and full coolant level).

The answering machine for the Omaha Saab dealer tells me their service department is closed on Sundays.

Is it safe to drive back to Minneapolis with a thermostat stuck open (370 miles, all interstate)? Or should I wait until Monday, get the thermostat fixed, and then go home? (I'm assuming I should avoid the Sunday mechanic at the neighborhood 24/7 chain gas station).

I'd appreciate some quick feedback - I've got to get back to pick up my daughter from my sister-in-law's place, and the earlier I need to make phone calls to cancel, reschedule, etc, the better.

Thanks in advance for the help.

13th March 2005, 02:27 AM
Well, I wish I could give you a definitive answer, but I'm new to Saab. I can say that on the vehicles I deal with every day, a stuck open thermostat will cause odd transmission shift changes due to the PCM seeing the engine as not being at operating temperature. The CEL comes on because the engine isn't at operating temperature and because of that isn't meeting EPA requiremtents.

That said, I've yet to see any damage from driving with a stuck thermostat, well...stuck open thermostat. Stuck closed is obviously a different story.

Black Beauty
13th March 2005, 02:35 AM
I appreciate the help. Googling "driving with stuck open thermostat" has given me some interesting results. One concern is that the engine is running too cool, and consequently with a fuel mixture too rich, sending unburnt fuel into the exhaust. This is then burned in the catalytic converter, causing it to heat up higher than spec, and potentially causing failure of the cat. An expensive fix.

I don't know if the T7 system would control for that, or not, but that seems to be the big problem with driving with it stuck open (that, and excessive wear resulting from too cool operation).

My gas mileage coming down on this trip was only about 25-26 mpg - I wonder, prior to being stuck open, the thermostat has been failing to close completely.

I'm leaning towards getting it fixed before I go back.

Edit - my Aero is a 5 spd manual, so odd shifting behavior is not an issue (or at least the function of human error, not the thermostat :)

13th March 2005, 02:44 AM
Well, I believe that's the safest route to take. I do see the how it would create a condition that would shorten the life of the catalytic converter. I've never had to replace a cat for that reason...knowingly. I never had to replace a cat on a vehicle that also had a history code, or current code, for low engine temp. And 370 miles isn't that far...relatively speaking.

Edit: Now, if this car only had 50k or so on the odometer, I'd say go home. The cat is covered for 8/80 under federal EPA regs. But, being that it is over 80k, I'd play it safe.

13th March 2005, 09:52 AM
Its a difficult call, Its a fare distance to travel. It would be a rail pain if you set off and traveled 50 miles to find out you cant go any further for whatever reason. Mine failed a month ago but it was closed :o That was really fun I had to limp 25 miles at a max speed of 20 mph to stop the coolant from boiling out.:( I dont think I would risk that soet of distance..

Finn :confused:

13th March 2005, 02:21 PM
I wouldnt even dream of driving that far on a cooled engine unless its a matter of life or death :nono;

Engine temperature is crucial to optimise component operation and that journey may add years of engine wear in one swoop

Dont mean to be too pessimistic here :lol:

13th March 2005, 04:44 PM
Why chance it? Rental cars are cheap. The worry alone is not worth the cost.

13th March 2005, 08:35 PM
I have a question for anyone who can answer it. My 2000 9 5 has passive turbo system. I have replaced the turbo twice in its five year span and it has just broke again. Any tips or does anyone know if of a fix to the problem? Has it happened to anyone else? Any feed back with be greatly appreciated sorry to be so off topic.

Black Beauty
13th March 2005, 10:18 PM
Well, I did it - made it safely home without having the thermostat replaced. (There were a host of reasons why waiting a day would have been very difficult - not quite life and death, but severe problems with child care would have occurred had I waited).

And I think the car is OK. Figuring I needed to stop excessive cooling, I used the old "cardboard in front of the radiator" trick (something we're used to see in frigid, sub-zero weather, but which I figured might work at 40 degrees F as well).

I think the thermostat was actually working for about half the trip - plenty of cabin heat and the temp needle was slightly under the middle (9 o'clock position). No CEL, either. And the SID was estimating mileage at 30 mpg traveling at 75 mph. So far so good.

After I stopped for drink and a restroom break, the CEL light came back on. The temp gauge dropped down to the 8 o'clock position, but was still clearly in the indicated operating range. Cabin heat was available, and the car ran normally. The SID reported mileage at 25.7 mpg (which might be explained by the fact that the second leg of the trip, from Des Moines to Minneapolis, is slightly uphill and there was a medium head wind).

So first thing tomorrow I'll have the car into my trusted independent mechanic, and we'll see what the deal is.

For what it's worth, I turned over 100,000 miles about 45 miles from home.

Thanks for all your advice -- it was very helpful. If I'd been driving a stone cold engine, I would not have continued the trip, for the reasons outlined above.

15th March 2005, 07:16 PM
Well done for getting home, hope you get fixed ok.

Finn :)