# DIY: Linear / true coolant temperature gauge in cluster



## maltestenzel (May 26, 2006)

<Applies to Golf 4, Octavia 1u and similair cars before Golf 5>
As you may have noticed, the coolant temperature gauge flat lines at 90°C for the temperature range of roughly 76°C-106°C. This has been done to give the customers a false sense of safety.
Now I don't need this, and I don't want it either. I want to see my true temperature. And actually, you can do it:
You need a way to modify your clusters EEProm. There are programs out there you can use: For example VagDashCom or, in my case, Vag Tacho (Tacho is german for cluster).
You need an interface cable, Vag Tacho 2.5 runs with an older, simpler one. You can use that interface with a FTDI driver which also supports Vista (and even 64bit).
1. Obtain VAG Tacho and an interface.
2. Connect and install the interface, use FTDI drivers from their webpage. Install as USB controller!
3. Connect the interface to the OBD port of your car, turn the ignition on.
4. Start VAG Tacho and select "Connect any Tacho". If the connection fails very quickly, try starting VAG Tacho v. 2.2 and hit Connect any Tacho. If it works there, close VAG Tacho 2.2 and start 2.5, it will now work. Might be some kind of initialization problem.
5. When a connection has been established, choose your ECU from the menu and click on "Connect Selected ECU".
6. As soon as this has been successful click "Read EEProm".
7. When done, click File->Save File
Now you have extracted your EEProm. You will need a hex editor like the free HxD to view and change your EEProm.
Around the Offset 0x02E0 - 0x0330 you should see something like this:
33 00 33 00 F5 02 F5 02 EF 04 B6 05
Read the values in pairs of four digits (33 00, F5 02, ...)
Your values may vary, but the first two should be low and the same whereas the third and fourth should be higher and the same aswell.
To convert your values to decimal, you need to switch the first two digits with the second two:
33 00 > 00 33
Then you can use the Hex>Dez tool from here:
http://www.vagdashcom.de/html/download.html
And your result will be 51.
All values converted:
51 
51 
757 
757 
1263 
1462
Now you can see we have a lower flat line (Leftmost position of needle) and a flat line in the middle (the 90°C flat line).
If you want to make a diagram, the x-axis values are stored directly before, in my case
F0 00 90 01 50 02 60 03 E0 03 10 04
To decimal:
240 400 592 864 992 1040 
This x-Axis represents the reading from the temp sensor. The Y-Axis values represent the amplitude of the temp needle. The cluster internally calculates values in between by this map.
You would want to change the two 757 (F5 02) values (your own may vary), so that you get a linear gauge respone. 
Your best bet is to use excel to draw a diagram with old and new values and as a rough orientation you can calculate the middle 90°C values by the rule of three.
After some testing, these values work well for me:
51
51
550
1020
1263
1462
Now converting back to hex, remember to do the switch (00 30>30 00) and you receive:
33 00 33 00 26 02 FC 03 EF 04 B6 05
Save the file, establish connection to your cluser again if you have disconnected in the meantime, select file by clicking File->Read file and then Write EEprom.
When done, click disconnect and turn the ignition off. Now wait a couple of minutes or the new temperature map will not be active!
Use vag com to compare the readings of your gauge with actual sensor data and adjust your eeprom accordingly. I had to raise the first replaced value as the gauge showed lower temps than actual sensor data.


_Modified by maltestenzel at 3:35 PM 6-12-2009_


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## RemiRokosa (Jul 12, 2008)

*Re: DIY: Linear / true coolant temperature gauge in cluster (maltestenzel)*

so how often do you see the temp needle vary on hard driving?


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## maltestenzel (May 26, 2006)

I just did a little test drive, ambient temp 12.5°C
Highway
Downhill 80°C
Part throttle 60mph 84-86°C
140mph 90°C
Ordinary road
A little fun, but empty 89°C 
---------------
City
Stop and go 95°C
So your coolant temp does not raise as much as the oil temp probably does on highway as you do have more airstream, but it does vary about 15°C. And when you get into a congestion you can react more quickly if you begin to overheat.
For someone like me without an oil temp gauge its better as well since its no longer showing 90C coolant when its only 76 or so.

_Modified by maltestenzel at 4:08 PM 6-15-2009_


_Modified by maltestenzel at 4:11 PM 6-15-2009_


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## groggory (Apr 21, 2003)

Adding this to the 1.8t FAQ


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