Knowledge Base

Instructions and shopping list to install sensor to monitor CC core temps

(Update April 06 - I have recently changed some of the components of the circuit as some were no longer available.)

The idea of this sensor was just to give me confidence in my CC system. I was worried that if the pump or other part of the CC system failed that I wouldn't know about it. I think this mod (or similar) is a must if you fit a CC. This is a guide for fitting a digital temperature sensor to your ST205 CC Core. I have written this as a very basic guide assuming that you have some basic electrical/MR2 knowledge. Remember what you do to your own car is up to YOU and at YOUR own risk! Feel free to PM me if you need to ask any questions or if you find an improvement. This is a very easy mod. This is the third version of this mod using an improved circuit. A problem was found with the initial circuit where small power drops in the car circuit caused the circuit to drop out and not restart properly. This circuit has already proved itself once when my CC pump stopped working.

Firstly this is a list of parts I used -

http://www.watercoolinguk.co.uk/catalog/product_info.php'cPath=45&products_id=64 - Display '5 plus postage

http://www.maplin.co.uk - 12v to 5v converter circuit. You will need the following components to make the circuit. (I ordered 2 of everything incase I broke a component with my poor soldering) These components cost me '2.66 (for 1 lot) at the time I created this article.

2x BX03D
1x CH35Q
2x VH57M
1x QF60Q
1x QL79L
1x G47R

I also used a little bit of wire and some connector block '2 from car spares shop.

Tools needed are some wire snips, a small screwdriver, a multi-meter, a solder iron, superglue, electrical tape and a drill with a small drill bit.

Firstly using the components from maplin I created a small converter circuit board to convert the cars 12v down to 5v needed to run the display. I glued the components onto a piece of plastic then soldered 3 the wires on. (I had never soldered before but managed it) Once I soldered the wires on I covered the piece of plastic and chip with insulation tape. Circuit diagram is below '

Next remove the stereo. I spliced from the 12v ignition live to the stereo to take 12v for the circuit board I just created. I then earthed the circuit board to the stereo chassis. You should now be left with 2 wires coming from the circuit board. One should be 5v whith the ignition is on and the other an earth for the display. Test it now with your multimeter.

Next push the temp sensor probe up the overflow of your CC. Take the cap off the CC and use your little finger to make sure the probe goes into the coolant. Now you will need to run the cable from the engine bay to the din slot under the stereo. I used the small grommet in the firewall on the driver side of the engine bay. I then ran it behind the carpet on the cabin side of the firewall and under the centre console to the din. Its very important that you dont run the signal wire from too close to the ignition wires. This will almost certainly knock out the sensor when the engine is running. (Thanks to Andy K who noticed this problem) If you find that the circuit is being knocked out from the ignition leads you could try and shield the wire with fuel line rubber.

Next you will need to mount the display. I drilled a small hole in the din tray and fed the wires through. You now need to connect the wires up behind the stereo and put everything back.You now have a digital temp sensor for you CC!

Thanks to guys on IMOC who suggested these parts to me.

Rory 01 Sep 2005 (Last edited 18 Apr 2006)

: Thu Aug 30, 2007 11:33 am

That same website now do a 12V-5V converter (and it specifically mentions 'for use on cars') so this mod is even easier to do now, and no need for soldering components...

: Mon Sep 17, 2007 5:55 am

: Mon Sep 17, 2007 12:35 pm

: Mon Sep 24, 2007 5:48 pm

i bought one of those converters , it was tiny , so hard to get them connected to anything , i managed it in the end and when i turn the ignition on , its just went up in smoke. where does it say for use on cars ? maybe i have the wrong link .

: Fri Sep 28, 2007 10:05 am

I tested mine and it worked a treat... the temp gauge was very quick to respond as well - if you grabbed it, it would go up about 0.5s after you'd touched it... so no response lag...