I'd definitely try replacing that CTS and see what happens. Those things can drive you nuts.

 

CTS = coolant temp sensor? The one under the intake manifold, back side of the valley (between the heads)?

Is there one sensor that runs both the ECM and the gauge? I'm curious as to why one reads correctly and one doesn't.....

 

By 2003 all Saturn's likely had a single cts that drives both the dash and is measured by the PCM.

Running temp sounds about right for said thermostat.

Not sure what you mean about one reading correctly and one not. If you mean why is the dash gauge reading low, my answer would be that it reads where it reads, had no temp markings on it, is nonlinear. However, if it is reading differently than it used to, that's a different story.

 

A new development!

This weekend we took out the Vue for a cruise to the in-laws. I pulled out a few misfire codes (300/301/303/305), but also found a stranger..... Code po440. IIRC, this has to do with the evap system, correct?

Is it possible I've been chasing my tail all this time for a bad gas cap or bad vacuum line in the evap system?

 

Anything is possible, Joe. Try removing the gas cap and give the filler neck and the cap a good cleaning. If it has an O-ring on it, remove it, clean the gap where it sits and then give the O-ring a coat of WD-40 and reinstall it. I don't know the history of the car, but a LOT of people have a bad habit of keeping the gas pump going after it clicks off. This can force gas into the vapor line and eventually saturate the charcoal filter. I NEVER keep it going. When the pump clicks off, I round it to the nearest nickle and stop. I've never had a charcoal filter problem with any NEW car I ever got. I did have it once with a PT Cruiser I had. 5th owner of it.