My guess is you have the same EXACT car as me...a 2001 MC SS. I just went through all this stuff myself.

It's either 1 of 2 things. Thermostat or Coolant Temperature Sensor. BOTH were inexpensive to replace ($4.95 for the Thermostat, $12 for the Coolant Temperature Sensor.

Best thing to do is to take it to Autozone or Advance Auto and let them put the diagnostic Tester on it. If the error code is P0128, then it is definitely either the Temperature Sensor or the Thermostat.

Personally, I'd replace the Thermostat and the Coolant Temperature sensor at the same time. The Sensor is right below the neck where the thermostat housing is. There's a couple of wires sticking out of it. So, drain your coolant (might as well give it a good flush while you're at it), take off the thermostat housing, replace your temperature sensor, then replace your thermostat and put your thermostat housing back on.

Here's the link to when it happened and what I did:
https://montecarloforum.com/m_19484/tm.htm

By the way, I noticed that my instrument cluster was kinda dim during these issues as well. But after I got the check engine light to stop coming on...the cluster got brighter again. It might be because the "check engine" light is pulling power from the instrument cluster lamps...and making it dimmer than normal.

 

funny thing is, I don't have a check engine light [&:] Where is the drain for the radiator so I don't get really messy doing all this? I'm going to get the PCM checked for any codes and I'm going to go buy the thermostat/sensor. Would you reccommend the stainless steel one or the fail-safe one? (stays open if it overheats?)

Yes, it's an 01 MC SS just like yours

I've never actually flushed a coolant system before. What exactly do you do? Just drain the old fluid and put new stuff in?

 

I just went to o' reilly's and there was a code "P0128." I'm going to replace all the stuff now, wish me luck!

Also, the new sensor came with an extra pigtail to splice in, do you think I should do that?

 

an extra pigtail? Weird. Mine actually came with just the female connection at the top. Maybe it's a ground? Maybe it's the wrong one. I'd check it again...or make sure that the one you get from the parts store looks exactly the same as the one you're replacing.

As for your lack of a Check Engine light...if you gave it time, sooner or later it would have popped on. Mine took a while to pop on too after my temperature gauge stopped working.

Anyways...to drain your coolant, disconnect the airdam at the bottom of the car. It gives you much more room to work with and it should be 10mm sockets to loosen the 5 bolts that hold it on. Then, on the Driver's side of the Radiator...at the bottom, there's the plug. It takes a 3/4" socket. It's plastic, so be careful not to strip it. Anyways, it shouldn't pull all the way out. Just loosen it and then the coolant will pour out.

As for Flushing the coolant...Do what the manual says. Put the drain plug back in, spray water in the top of the radiator, let the engine run and put on the heat full blast. Then, after it's gone for a while, shut the engine off, let it cool, then drain the radiator again.

 

I guess it would help to read the instructions first. I spliced the new pigtail in and then it said that you only have to do that on the older style ones that have the round pin connector. I couldn't find the drain plug (I did this before I read your post) so I just dumped it into a funnel that lead to a bottle. not too much spill, until I got to the sensor. All in all it wasn't that bad to replace. Easier than most jobs. I didn't feel I had to flush because the fluid was REALLY clean. I will probably flush it this summer though. I replaced it and started it and the fans were still on and the temp gauge wasn't moving. I was about to go to the auto store when everything started working. My operating termperature is higher than it was when I bought it. It's running where it's supposed to now. The heater works a lot better now. I'm very happy that it was one of those two.

 

Did you replace your thermostat too?

Yeah, mine's running a bit hotter than it was prior to replacing everything as well. Probably because you got used to it running slightly lower than normal. If you look though...it should be around 195 degrees.

 

Yep, I replaced the thermostat too. It's running about 195 like you said. I noticed the stamp on the thermostat was 195. I'm very pleased with it now because it doesn't take as long to warm up anymore.

 

Glad to hear all is well now. Same thing here.

I noticed one more thing. One of my co-workers told me that the Tranny fluid goes into the radiator as well to get cooled. I didn't know this. Anyways...the car started to shift very hard when it got hot. Now that the Thermostat and Temperature sensor has been replaced...I noticed that there isn't any more hard shifts.

Amazing how things are tied into each other.

 

very nice to hear that the problem is fixed now

so it was the temp sensor then??? stupid that those things go all the time, but at least its an easy and a cheap fix

 

I don't know if it was the temperature sensor, Wiz. I replaced the Temperature sensorfirst...but the temperature gauge still did not work.

Then I brought it to Autozone, they put the diagnostic on it and it came up with a P0128 error code. They cleared it...and that's when the temperature gauge started working again...and the check engine light turned off. The guy said that sometimes you just have to clear the error code because the computer doesn't know that you've replaced the temperature sensor. Much like resetting your Oil Life Sensor after you change your oil. So it COULD have been just a Temperature sensor and a error clear that fixed it.

But rather than take the chance...I replaced the thermostat and coolant as well...just in case.

In either case...it was a low-cost solution. Only $25.00 (temperature sensor, coolant and thermostat). And it worked.