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Low engine temp problems, 9-3 1998

1K views 17 replies 8 participants last post by  BobSaabit 
#1 ·
So I recently replaced my thermostat, because my engine temp was always at the lowest when driving on a motorway, and in city traffic it would fluctuate a lot. Replacing the thermostat fixed the issue, well I thought it did. It warmed up really well, and stayed in the middle of the temp gauge all the time. And it was working fine for a week, until today when I drove for ~40 minutes, It warmed up pretty slowly (Was raining and 7 degrees celcius outside at the time) and reached the middle after driving for ~5-10 minutes and stayed in the middle for 30 min. I stopped the car, and had it turned off for 5 minutes, started it up again, and when I got out on the motorway it went to the lowest temp on the gauge.

After getting into the city it slowly reached 1/3 from the bottom, and then I reached my destination and haven't driven anymore today.

So is this normal for "Cold" weather and in high gears / low rpm on the motorway? Or is something broken?

May I also add that the AC worked fine on the warmest setting, blowing out hot air as it did the day before.
Also, the car temp usually stays really close to the bottom of the temp gauge, but after driving for about 2-5 min it would jump straight up to half way in a few seconds. Is this how it is supposed to work? It takes a long time to warm up on idle (5-10 min), so I usually drive it in low rpm before it reaches the middle.

Any help is grately appriciated!
 
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#2 ·
Engine temperature should remain very consistent... that's what the thermostat is there for.

You need to determine whether the thermostat has failed or if the gauge is reading incorrectly, or if there is some other issue. Easiest thing to do IMO is monitor the engine temperature with an OBDII tool ... that should give you a clue.
 
#5 ·
Ah ok, don't you think it seems weird when I just replaced the termostat a week ago that it would fail again?

I currently don't have an OBDII but I'll try to get hold of one. Also, about how long should it take for a cold engine to reach half way on the temp gauge?
 
#6 ·
"Half way" doesn't actually mean anything, since the gauge is just a range of temperature. Generally speaking, the engine should be warm within 10 minutes of driving.

Not all thermostats are created equal - if you used an off brand, yeah, it could have failed. If you use a Saab thermostat or OE thermostat, then I would expect it to be reliable.

Regardless, I wouldn't go about replacing anything til some diagnosis is done... it's important to determine whether the sensor is wrong, the gauge is wrong, the engine is actually cold, or there is some other problem. Checking the gauge sensor against the engine coolant temperature sensor is the easiest/first step IMO. Failing that, you can check to be sure the upper radiator hose is hot, and the radiator is consistently hot across its surface.
 
#7 ·
Ok, will feel the radiator and the radiator hose tomorrow when the engine is relatively hot. Oh and one more thing, should the engine get up to operating temperature in 10 minutes on idle aswell? Or will it take longer / shorter compared to driving it when it's cold?
 
#9 ·
Ah yeah, I can imagine. Thanks a lot for the help and all the clear awnsers! Will try feeling the radiator tomorrow, and seeing if it feels hot all over. Pretty cold and very rainy here in Sweden aswell, so that might also have been a part of the low temp problem, not sure though.
 
#10 ·
Use IR thermometer and check actual temperature.
Sounds that you have either bad thermostat or bad temp sensor/its wiring or connector.
OBD reader will read same sensor that temp gauge.
 
#12 ·
Almost always, the fully warmed up engine should read halfway on the gauge.

It might drop if the weather is cold (-10º or colder) and the heater is going full. This can happen even when driving at speed on the highway, and more if the engine is idling.

Otherwise, needle should not drop from halfway.

I agree with Mimmi, you have to see what is going on.

I tried an aftermarket thermostat made for my car, and it still did not work properly. Temperature dropped on the highway (even in summer). An OEM Saab thermostat fixed that. Both were made by Motorad!
 
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