After driving the car for about 10-15 minutes, the car begins to stall. I watched the RPM start to drop along with the tempreture gage go from cold to hot in one second. The one other thing I noticed is that the red temp icon lite up for a second and then switched back off. The mechanic that I took the car to switched out the following parts.

EGR (This part was swapped.)
ECTS (supposedly I was not able to visually verify this)
battery (replaced it since it was 5 years old)

The mechanic was stating that he thought it was the alternator. I disagreed with him and took my car home to try and find the correct solution. My thought is to verify that the ECTS was really swapped out.

Any ideas?

 

First of all I hate acronyms. Each manufacturer of a car comes up with pretty much their own acronyms of what things are and as far as I am concerned they are meaningless if I have to look the dang things up.
If you mean by ECTS the Engine Cooling Temperature Sensor located on the drivers side of the end of the cylinder head that would be a very good thing to do, to verify the fact it was changed or not.
In addition the Saturn is pretty sensitive to the calibration of the thing and it's operation. Despite the fact that it can be out of calibration and the car run that way for years before it starts to hiccup and act badly. And that is the problem. Or a problem anyway.
Discussing that and that alone, it took years before Saturn actually recognized it as a problem and manufactured cars with the wrong one in them. The aftermarket came up with replacements that are also the wrong ones. And if the stupid thing is or some how becomes defective and the connector can be too, the car CAN act just exactly as you are describing.
So thoughts!!!
Your mechanic is dumber than a bag of rocks.
But that is an opinion.
The only way at the present to verify you have the proper ECTS is to actually order one from a GM dealer that can and will order Saturn Parts. They finally got the right one in GM parts stock.
Aftermarket?
At this point in time years after the fact, if the only one that is available is an after market on I would use it but watch it carefully.
The temperature gauge is driven by the engine management computer looking at the value of that sensor. If it is gyrating madly it is an indication that the computer that drives the gauge things engine temperature is gyrating madly. As that sensor is also a key element in how the engine runs it will cause the engine to run all kinds of bad, just saying.
Whether it has been changed or not, there is a possibility the one in the engine is bad.
It would help also to have a list of codes the computer thinks are problems.
They all go together.
The day where simple things can be determined are pretty much gone. Observations PLUS problem codes are almost imperative when it comes to diagnostics.
If you know how to get the Saturn computer to display codes with out a code reader that can be done. The instructions are in the smog section of a "how to fix your saturn" book. About $30.00 or so. Or get some one to read the codes, Autozone or O'riely. I don't have a scan tool as of yet. I have not really needed one. However if my Saturn was acting like yours, at about $150.00 or so I can buy a passable scan tool that would read codes in my Saturn, my Chrysler and my MultiPoint Fuel Injection Conversion complete with California CARB smog exemption certificate that I use in my 1980 Fuel injected smog legal modified 258 cu in I-6 conversion that is faster than snot.
The very first time I would have to use a scan tool would pay for the cost of it by not having to pay a mechanic who is dumber than a bag of rocks to tell me he changed the battery because it was 5 years old rather than there was something wrong with it causing a problem and when it did not fix anything changing it then tell me I needed an alternator.
So check the Temperature sensor and it's connector and see if you can get codes read out.

 

I'm kinda with UnclJohn on this, but I will make the comment that among other things, Saturns are notoriously sensitive to voltage fluctuations. Assuming that all the interconnecting cables are good, then replacing a five year old battery and an alternator does make some semblence of logic. Personally. I would have stopped at the Engine Coolant Temperature Sensor (ECTS) and it's associated electrical connector, and re-assessed the problem.

 

https://www.saturnforum.com/forum/general-tech-help-13/etcs-its-connnector-6417/

 

I am my own mechanic and unless something is way out of my league or I just do not want to deal with it, my answer comes from my own experiences.

My Saturn experience is owning the same car since about 1998 and in addition maintaining a friends Saturn for about 5 years I can not confirm or deny the comment on sensitivity to voltage fluctuations. I never saw that as a problem. Although I have had a problem with the Alternator on my Saturn and had to replace it.
What I can say simply is this. Harbor Freight sells a digital voltmeter on sale for $2 or $3.00 and is normally about $8.00 and I keep a couple around. They work just as well as the special Digital meter that had a range on it not normally available and at the time cost almost $200.00 I needed to service a product I worked on.
If an alternator or a battery is having a problem it is not rocket science to use one to measure the voltage and determine there is a problem with one or the other and then based on that measurement change the defective part.
To pay a professional mechanic their wage and about $60.00 an hour is expected plus premium prices for a battery and an alternator to replace one because it is 5 years old and the other as a guess when 2 min. making a measure of voltage as a diagnostic or even pulling out a scan tool and checking for error codes a procedure that that should be automatic as a professional is not my idea of a correct repair procedure when you are paying some one for doing it.
I don't care what you are told they thought the problem was but from your description you were told one was old and the other for no reason at all. The mechanic was dumber than a bag of rocks. There was no no expectation that doing those things would effectively repair anything. Both suggestions were at best wild assed guesses.
As a shade tree mechanic I at the present have not had to deal with a problem I could not solve easily with out a scan tool. I have had to resort to using the on board diagnostics a couple of times to pull up error codes to help with the diagnostics, my Saturn and my AMC Spirit both have that capability. A bit of a pain in the butt to use but they are there, my Chrysler does not.
I can at this point in time go down to O'Reilly's and buy a scan tool for about $150.00 that will save me that plus some the very first time I use it if I have to. That cost is cheaper than a Battery and an Alternator together.
A friend of my has am 8 grand scan tool plus the expense of a real time up date subscription that can just about tell you your driving history on damaged cars before and after the repair to validate a warranty. He is a professional and the tool saves him far more than the money it costs to buy it.
I will not pay good money to have some one guess what is wrong with today's cars. They are far too complex to spend my money which is hard to come by to be able to have the luxury of subsidizing some one elses life.
The engine temperature sensor on the S series Saturn's are a long term design problem and a matter of record that when the history is checked on the problem started with the first one built and was acknowledged with a service bulletin some where around 2000 or so. A problem that never should have happened and waited way too long to be identified. But strangely enough these cars will run a long time with out any problematic indications something is wrong but when it finally shows up goes from no bother to catastrophic almost over night. Mine became a problem some where around 1999 and when identified and corrected by using the correct part disappeared back into limbo.
This problem as described can be diagnosed by
1. Using a $2.00 digital volt meter
2. Supported by having the capability of identifying the codes
and
3. Sounds as if the ETCS is still part of the problem despite having been told it has been changed.

As 1 and 2 have not been done 3 is at best a wild assed guess.
But it fits the description of a possible candidate.

 

Thank you for the information.

I am going to try and change out the ECTS today and see what happens. I am also looking at purchasing an Actron scanner. Any thoughts on the brand?

 

if you plan to maintain your car in the future, be sure to get the one which reads real time data --shouldn't cost more than 30 or 40 more than the basic

 

Get the ETCS from the dealer in a GM packaging and replace the connector also bought from the dealer.

 

So I ended up buying the ECTS along with the connector from GM and swapped them out today using the steps that richpin posted online. At first I thought the issue was resolved, but the symptoms returned after I started driving a few minutes. The temp gauge jumped from hot to cold and there was hesitation when pressing on the gas to accelerate. I also had the temp warning light flash red an turn off.

Any ideas?

 

And the error codes read out were?