How to modify a 24V HZJ75 water temperature gauge (1 Viewer)

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Jun 29, 2010
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Location
Switzerland
So, after reading lots of instructions I could find nowhere an instruction for my 24V HZJ75!
I removed the gauge a few times and saw that it was completely different than the ones posted here!
Since I'm traveling since 2 years my possibilities where very limited!
Here in Ecuador I had overheating problems and I took the chance to get this gauge work as it should have from the factory!
I removed the original sensor from the cylinder head. It's just above the oil filter a little bit on the right side. Your wrench extension will touch the oil filler tube. It's a very small sensor with a small connector that you have to remove first. Oh and drain some coolant before to avoid a coolant mess!
Here you see the sensor on the last picture, just right of the oil filter:

https://forum.ih8mud.com/threads/1hz-temperature-sensor-location.365517/

First remove the GND from the battery to avoid short circuits.
After that you have to remove the gauge. The only hard task is to get the speedometer cable off! It was a real pain since I hardly could get behind the dash to get it off! Took me about 15min of swearing till I had it off!
Once the dash is out remove the front plastic cover and turn it around and remove the gauge. It got only 3 small bolts. Careful that the gauge doesn't fall out when you remove the bolts, hold it with your gloves (to avoid fingerprints on the black gauge background)

Here you will find that diode that is the reason of the idiot behavior of this gauge!
Unsolder it and install a 143Ohm resistor (it's on the E96, not super common but you can find it!). I didn't have this possibilities down here in Quito at some garage, so I took old radios from a box that were laying around and soldered more than a few resistors parallel till I got the right value. It was lots of trial & error for me! Not nice looking but it works!
The power of the resistor seems to be no problem, I would install a 1/2Watt or even 1Watt to be sure. My resistors don't seem to get hot at all but it's a lot of resistors and they can distribute the heat.
When measuring I would say it generates about 1/2Watt max...

Anyway, solder the resistor on the bottom like I did. I did use some wires to connect the 3 terminals of the gauge (with the original bolts) to my dash and put the gauge on the steering column. Careful not to drop it! Also CAREFUL that your dash doesn't touch the metal frame! I put some rubber on the bottom metal frame. It could make a short circuit on the bottom traces of the dash with the metal frame!

In the engine bay I used 2 wires, one connects to the original sensor connector (1 pin) and this goes to the sensor. Just take small electronic clamps. Then connect the sensor outside hex nut with another clamp and connect it to a good ground. VERIFY that your ground where you connect it is the same as the one on the dash frame!

Reconnect your battery.

So, I took a cooking pan (don't take the nicest one! We got only 2 and my wife was not very happy afterwards with all the burned oil in the pan! :) ) and put some vegetable oil, heated it up to let's say 110Celcius and put it on the engine (use some isolation to protect the valve cover etc.)
Use a good thermometer and put temp sensor and thermometer inside the hot oil.
It will take about 1 minute for the sensor to get the right temp.
Turn on your ignition. Take care that the gauge needle is free to move!
It should now move near the red position, depending how hot the oil is. Let it cool down to 90Celcius. Move then your thermometer to be sure you measure the right temperature the sensor sees.
I waited till I got 90Celcius and it just went to the middle of the gauge! I made a small line with a marker and made also lines at 80Celcius and 70Celcius.
Removed the sensor and recooked the oil to 140Celcius. Now back to the engine and sensor back in. Now I waited till it cooled down to 130Celcius and made the line in the red, at 120 it was still in the red, 110 outside red, 100 again a line and 90 I was again at the same spot as before. (see picture) I made just every 10 Celcius a line.
It's not super accurate, but I would guess still +/- 3 to 5 degrees and surely 100 times better than the stock gauge!
If this works, you can reinstall the gauge, the stock water temp sensor and go for a test ride!
I cut out some lines from a sticker label I had, so I see the lines better. To have it just made super cheap from old radios for 0Cents it doesn't look bad!
Still, it takes a few hours till everything works as you want it!

Have fun!
If you have any inputs or comments let me know!

diode_replaced.jpg


resistors_bottom.jpg


lines.jpg


white_lines.jpg


final.jpg
 
Last edited:
How did you know to exchange the diode for the resistors? Genius!

Was this same poor-design gauge used on other models?
 

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