View Full Version : Interior temp gauge not working.

02-03-2011, 07:14 PM
2000 Saturn SW2 with 128K miles.
Regardless of the temperature of the engine, my interior temp gauge does not work. When the car is warm, it will move at most if at all a 1/16" just up to the very first line then stop there (no reading).
My first instinct was to replace the temperature sensor under the hood which of course yielded the same results. I've purchased an aftermarket thermometer but I'm afraid of bypassing the original sensor in fear that it will affect the performance of the car. Has anyone else dealt with this? If so, what were your solutions?

Thank you for your time.

02-03-2011, 07:29 PM
You are correct that you cannot bypass the coolant sensor as the coolant sensor not only provides a temperature reference for the gauge to work correctly but its crucial as one of the main inputs to the engine computer without which would create serious engine issues.

Did you replace the t-stat at any time or is the one on the engine the original one? The t-stat determines true engine coolant temps and not the other way around. The t-stat provides the optimum running temperatures for ideal engine/emission operations. The coolant sensor only provides temperature signals to the engine computer and does nothing else. A faulty coolant sensor simply provides incorrect temperature signals while a brass replacement sends correct signals. If the t-stat is running colder than normal then the coolant sensor is just reflecting the colder running engine.

Most owners replacing a faulty coolant sensor tend to forget or ignore the importance of the t-stat. A faulty t-stat simply runs the engine cooler than normal and is usually felt as lack of heat for the interior. Once replaced, heat is abundant, the temperature gauge shows the needle between the 1/4 and 1/2 tick mark, the engine warms up quicker, and fuel mileage increases.

Use a 195F replacement.

02-03-2011, 07:46 PM
Good point.

However, shortly after replacing the temp sensor with the brass model, I noticed a leak from the radiator (probably there before). I replaced the following all with new parts:

Upper Radiator Hose
Lower Radiator Hose
Thermostat (and seal)
Upper trans. Cooling line.
Lower trans. Cooling line. (both turned out to be a huge burden).

My thoughts were that there may be a flaw with the actual mechanism that moves the needle. After removing the instrument cluster I found that it is not serviceable without removing multiple (7) plastic melt rivets. At this point I just put everything back together. I'm rather uneasy about driving around with a temp gauge though.


02-03-2011, 07:48 PM
**without a temp gauge.

02-03-2011, 08:05 PM
See if you can get your hands on a real-time OBD-II data reader. Something like a Scangauge II or Ultragauge, or even some of the better hand-held scanners (Actron, et al). They will read, numerically (in degrees F or C), what the PCM is picking up from the ECTS. After a full warm-up, at cruising speed, that should be somewhere around 190F. If you confirm that, then indeed, you've narrowed down the problem to a likely mechanical issue with the gauge needle.

02-03-2011, 08:27 PM
Can the aftermarket thermometer read where its placed like on the hose coming from the t-stat housing? If not then maybe a hand held infrared thermometer can be used to spot check temps anywhere its pointed. This way you can compare readings against a possible faulty temperature gauge.

Short of these two recommendations, a replacement instrument panel from a junk yard is the only way to putting things back to normal.

What temperature t-stat was used?

02-03-2011, 08:31 PM
I'll have to save up some cash for a tool of this magnitude. In the mean time, does anyone have any suggestions for integrating the aftermarket temp sensor in addition to retaining the original?

02-03-2011, 09:02 PM
Drill & tap a new hole on the upper radiator hose bung(?) on the head. It'd be a good idea to drain the coolant & stuff a rag in there to catch any metal shavings. Same sorta idea people do when putting a 2nd gen head/engine in a 1st gen.

This claims it can read live data, only $50: http://www.amazon.com/Autel-AULMS310-MaxiScan-MS310-Reader/dp/B002IABWPW/ref=sr_1_3?s=automotive&ie=UTF8&qid=1296785107&sr=1-3

Amazon can't decide how much to charge for an Actron CP9180 (cheapest Actron with verified live data reading I know of), I bought mine for $115 shipped, they fudged with the price & shipping 2 days later so it looked cheaper but with shipping was like $3 more expensive & now they want over $130 before s/h :dizzy:

03-18-2011, 09:56 PM
Hi, im new to this forum and having the same issue with the interior guage. After reading around the site and having a few other issues with high idle, I think i need to replace the coolant sensor, to start, and I will also get a thermostat. (Although car heat is good) My question is, should I buy the coolant sensor from a Saturn dealer, or can I get it from the zone?

Some additional info from my issue is I've driven the car for a few hundred miles and when I take it to the shop to get a state emission test, they tell me that the car computer hasn't reached all the perameters to give me a scan. They told me to drive it for a hundred miles but still hasn't met all the perameters for the pass or fail. Im guessing that a bad coolant sensor never lets the computer to check since it thinks the car isn't reaching normal operating temps.

Guess im rambling a bit, but just wanted to tell the story since it might be of some help.

So the coolant temp sensor is where I will start, Buy from dealer or the zone?

Thanks for the site..

1999 Saturn SL-1
95,000 miles.

03-18-2011, 11:12 PM
To pass emission inspection;

1-Replace the coolant sensor if its the original faulty round nosed plastic one with the brass flat nosed one. Buy it from any auto store.

2-Replace the t-stat with a 195F one if the temperature gauge needle hovers over the 1/4 mark. Buy it from the same place you buy the coolant sensor.

Both parts will prevent the car's emission self tests from completing as coolant temps above (approximately) 170F aren't reached so most shops and the misinformed state to run the car for several hundred miles in order to have these self tests pass. Nothing can be further from the truth. As coolant temperatures are crucial to engine running, the moment one or both parts are replaced and everything else is right, the self tests will run and complete in as little as the first drive to work. The "drive cycle" term is what everyone becomes confused about and discusses to no end with differing opinions. For Saturns like yours, replacing a faulty coolant sensor and worn out t-stat will take less than a quarter tank of gas to compete the 'readiness monitors'.

03-19-2011, 08:55 AM
Well, replacing the coolant temp sensor was the issue with my car. Not only is the guage working now, the high idle is gone and runs and idles awesome.

Thanks for the help on this forum. Thanks fdryer for your good info.

You guys rock! :yes: