Subaru Coolant Gauge Problems

This article will explain some basic testing procedures and common fixes for problems with the coolant gauge. When diagnosing any coolant temperature problem the first thing you need to do is make sure the cooling system is operating properly and the vehicle is running at a normal operating temperature. If you’re having problems with your coolant gauge not reading correctly and it’s related to something in the cooling system you will probably find the problem during your cooling system operation inspection.

Check the fans are cycling properly and for proper operation of the thermostat. Next you need to read the coolant temperature sensor and if you have a scanner it makes it easy but if not, no worries you can just jump straight to the test you would have to do if you were having coolant temperature sensor problems anyways. Most every automotive manufacturer uses a 5v reference for their coolant temperature sensors. Then there will be a ground, check it and makes sure it’s good then backprobe the 5v reference and plug in the sensor. Monitor the voltage as the vehicle warms up (while running of course) and the voltage should slowly rise as the resistance drops in the thermistor.

thermistor
a semiconductor device having a resistance that decreases rapidly with an increase in temperature. It is used for temperature measurement, to compensate for temperature variations in a circuit, etc.

Now as for Subaru’s and cooling gauge problems there are basically only two things that I have go wrong with them in the years of working on these cars. There are other things that could go wrong but I just don’t ever see it. For example VW and Volvo are common to have instrument cluster circuit problems and instrument cluster control module issues, where the controller is located in the instrument cluster. So usually it’s going to be the gauge itself or the sensor. I will show you how to test and/or replace both. The sensor is pretty, look at the gallery pictures below to get an idea of its location. Now most vehicles use a two-wire temperature sensor and a one-wire sender that would be for the gauge. The other two-coolant sensor is for the computer. Subaru uses one dual function sensor so you will see a three-wire sensor. They share a common ground and the other two wires are volt references to the gauge and PCM. Find the three-wire sensor in the water crossover pipe under the intake manifold, just right of center. Black/Yellow wire is for the PCM, Black is the ground and the White/Green wire is the thermistor for the gauge. First check for a 10V reference from the gauge on the White/Green wire. Next ground the White/Green wire through a test bulb, something that draws current, not an LED test light. When you ground this wire the gauge should raise if it doesn’t then the gauge is faulty, if it raises then your problem is in the sensor. Now replacing the gauge is pretty easy, just be sure to inspect the instrument cluster circuit board at the main connector solder points, I have seen breaks there before in other vehicles never a Subaru though. You should be able to get a gauge from the Subaru dealer for less that $30.00 and the sensor is a little more expensive but either way this can be a relatively inexpensive fix that can prevent costly engine damage from not having a properly working coolant gauge. Well, that’s about it. Take a look at the gallery images below for pictures on hoe to remove the instrument cluster. These pictures refer to a 2003 Subaru Legacy. The older models didn’t require so much work to get the cluster out but these you have to remove a lot of trim parts and lower the steering column (2 bolts). Subscribe to my blog, LIKE my page, thanks for reading.

Donations

If you find this information helpful please consider a donation. These articles, questions and comments are very time consuming so even a small donation gives me motivation to keep educating automotive owners. Donations will allow us to continue open questioning/comments, automotive education and repair tutorials in the future as the business grows. All proceeds go to the expansion and maintenance mdhmotors.com. Thank You



Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development. MDH Motors offers moderated guest posts! Click Here To Submit Your Article For Review Please feel free to Ask a Mechanic if you have not received a response for your comment within 72 hours, thank you.

15 Comments

  • Bertrand says:

    I have a 2000 subaru forester.
    I had the water pump and distribution belt changed.
    The following week, the temperature gauge started to read hot after 10min. From that moment, it goes up and down but mainly hot. I paid for the expensive head gasket repair, new hoses and radiator but the problem persists.
    New water pump, new radiator, new head gasket…. I am puzzled.
    Help appreciated.

  • redseal says:

    i have guage with needle going pass hot range was working before in stalled sensor upon engin rebuild engin not running hot checked guage comes up when grounding white/green wire thought new sensor bad got new one same problem fans cycling new thermo inferred gun shows temp good would like to get working before driving any suggestions

  • Robb Macdonald says:

    This is very helpful information. My 99 forester has a needle on the coolant guage that goes way past H but it is not over heating. The needle just stays spiked. I ordered a temp sensor which is probably a reapair i can handle. If that doesn’t work then it is the gauge that needs replacement and that’s above my skill level. Thank you for saving me all the time investigating how to change a guage.

  • julie says:

    Hi, the dash temperature gauge has stopped moving on my 1987 Subaru do we stationwagon? The coolant is full, there hasn’t been any overheating…. Just no gauge movement no matter how far I drive. I don’t know if it matters but last week upon starting my car and taking off, large plume of white smoke came out of the tailpipe. Thanks!

    • Martin Hand Martin Hand says:

      Check the single wire coolant temperature sensor. Unplug it check the gauge then temporarily ground it while checking the gauge to see if there is any movement. If so replace the coolant temperature sender.

  • Cait says:

    Hello, I have a Subaru Legacy early 2000s I believe a 2001? That the temp gauge doesn’t move from the halfway point unless it’s off. I didn’t notice this initially but then my thermostat got stuck closed (and due to the gauge not working I didn’t know it was overheating hardcore) and I cracked my head gasket. Well I paid for the head gasket to be fixed and all that fun expensive stuff….but the temp gauge still doesn’t work. And I am looking at driving about 2,000 miles in December because I will be moving and I would really like to fix the issue. Also it’s been shifting a little hard sometimes and I was told it would just need the transmission services? But I don’t even know what that means in terms of anything. Like is my transmission going to go out or???

  • Fern says:

    My temp guage on dash displays about 2 mm above half mark on my 2003 subaru legacy b4. Im a female, just brought it in from japan last week. There arent really any Subarus where i live, barely mechanics that deal with japenese vehicles. I just want to know if its something i should be concerned about… I asked a random mechanic he said to just change the temperature sensor… before i buy any parts im trying to look up my problem.

    • Martin Hand Martin Hand says:

      It’s probably normal. I wouldn’t worry about it but if your still concerned the operating temperature should be from 195°F to 220°F. You would probably need an infrared thermometer. Don’t open the cooling system while hot okay.

Leave a Reply