Temp Sensor

I have a Saab 9-3. The temp gauge stopped working and the check engine light came on. Next time I started the car the temp gauge was fine but the check engine light is still on. I am told the temp sensor is the problem and needs to be replaced. This sounds reasonable but I am also told that when this repair is done they also change the thermostat. Does this make sense?

Depending on the set up (I don’t know how things are arranged on the Saab) it might make perfect sense, and otherwise it probably makes good sense. Thermostats, as parts, are cheap. It may be that there is a bunch of labor involved in getting to the coolant temp sensor that simultaneously provides access to the thermostat. In this case it makes perfect sense, and should add very little cost to the whole job. At the very least, the cooling system will likely be at least partially (if not fully) drained.

It may also be that one assumes that if the temp sensor went, then the thermostat is not far behind. The last thing a mechanic needs is to change a temp sensor, then have the thermostat fail soon after, and then have an irate customer assuming that it was his/her fault.

In general, some people (myself included) think that thermostats are a good thing to just change as a matter of routine whenever it is convenient (within reason - I don’t look at for at least 2yr/25K or so). So if it has never been changed, it is not unreasonable to recommend it.

One other possibility is that no one has actually diagnosed your problem, figures it is either the thermostat or the sensor and will just change both to be sure. That is not so good.

How much more are you being told that you will pay for the thermostat?

Close to 3 hours of labor just for the thermostat.

Who is to say that the temperature indication will ever recur? Have Auto Zone read the code, and turn off the light. The light may not come on again. If it does happen again, get the code and bring it here.

If that is a whole different 3 hours than anything w/ the temp sensor, then it sounds to me like someone has either not bothered to diagnose or is just looking for extra $$.

Do as hellokit suggested (below), or if you’re worried about it get a second opinion - it sounds to me like you need one. Is this a dealer or a corporate chain repair shop? If so don’t get a second opinion at a place like that. Find a local, reputable independent shop.

That is over and abpve cost to replace temp sensor. I will get the code as suggested by hellokit. Thanks all for advice.

The code is P0119

That code does not mean either “change the temp sensor” nor “change the thermostat” - what it means is that the engine’s computer is getting an “intermittent” signal from the sensor (P0119 Engine Coolant Temperature Circuit Intermittent).

This could be from a bad sensor. It could be from a bad thermostat, or even from low coolant. But it could also just be a bad connection in the temp sensor wiring (a break or chafe of the wires, a dirty connector).

So the real question is what the shop has done to actually isolate the real cause of the problem. The stories of changing parts not solving problems are endless because many people just change parts rather than pinpointing problems.

I think that it may be worth your while to get a second opinion. At the very least ask whomever gave you this “diagnosis” how they arrived at it. A faulty thermostat is probably the least likely cause of this trouble, and if I were you I’d feel perfectly comfortable telling them to skip the thermostat for now.

One caveat about proper diagnosis - intermittent problems can be very difficult to sort out unless you know exactly how to reproduce them. My own approach would be to carefully inspect the temp sensor wiring, pull and clean its plug, clear the code & see what happens. If the problem persisted, I would then pull the temp sensor and test it (easy to do with an ohmmeter & a pot of water that you can heat up).

I will go for a second opinion. Thanks very much for your help.