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Martyn668



Member Since: 17 Mar 2013
Location: Cambridgeshire
Posts: 78

United Kingdom 
Plug into temperature guage to get a warning light

Hi all,

How many times do we scan the dashboard and see the temperature guage. We might all keep an eye on the speedo, but honestly, the temperature guage? Having oveheated once (Td5) I have been pondering how to rig up a warning light/buzzer. It seems (to me as a non-programmer), that it should be relatively simple to break into the wire feeding the babck of the temperature guage, and use something like an Arduino or a Microbit to switch on a warning light or sound a buzzer. This avoids placing separate sensors and wires, etc.

What do all you electronics gurus think?

What is the wire telling the gauge? HIgher voltage? Higher frequency pulses?

Post #740759 15th Nov 2018 11:29pm
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ajps72



Member Since: 08 Jan 2012
Location: Lima Peru
Posts: 87

2001 Defender 110 Td5 SW Chawton White

the first alarm should be coolant level, and that is relatively easy.

I think it would be more relieble to install a second sensor and a light to control heat.

The indicator doesnt act linear to the temperature Augusto

Defender 110 TD5 2001
Discovery 4 TDV6

Post #740767 16th Nov 2018 4:49am
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Naks



Member Since: 27 Jan 2009
Location: Stellenbosch, Republic of the Western Cape
Posts: 1806

South Africa 2010 Defender 90 Puma 2.4 SW Alpine White

Get a Madman EMS or similat monitoring system - it will change how you drive your car!

Do NOT rely on the built-in temperature gauge: by the time it moves up, your engine is most likely toast. --

2010 Defender Puma 90 + BAS remap + Alive IC + Slickshift + Ashcroft ATB rear
2015 Range Rover Sport V8 Supercharged



Defender Puma Workshop Manual: https://bit.ly/2zZ1en9
Discovery 4 Workshop Manual: https://bit.ly/2zXrtKO
Range Rover/Sport L320/L322/L494 Workshop Manual: https://bit.ly/2zc58JQ

Post #740771 16th Nov 2018 7:44am
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davew



Member Since: 02 Jan 2012
Location: North Yorkshire
Posts: 880

England 1990 Defender 90 V8 Petrol PU Auto Rioja Red

I fitted a Madman to our TD5 about 5 years ago, alerted us to an issue with the coolant level while driving through Sydney on our way from the docks, not certain I wouldn't have picked it up anyway when checking BUT that simple warning saved a LOT of potential issues by alerting me before it became a problem.

An Arduino is more than capable of doing the same job though as a MadMan, I've never taken a MadMan apart but i wouldn't be surprised to see a similar processor in use. I have a project that's very much on the slow track to build my own monitoring gauge, one that doesn't need the dashboard modifying to fit. It uses a Nokia TFT display from a phone and a "lily pad" Arduino to drive it and to read in all the data.

EGT is measured using a thermocouple and adaptor module and there are an additional 6 analog to digital channels available to measure voltages, sensor inputs and so on, up to 6 PWM outputs capable of driving other gauges and up to 14 digital I/O pins for digital inputs and for switching lights and relays on/off. Some of those are used up by the display comms though.

I printed a test housing for it and have done some work with the display to check functionality. The housing is in yellow/orange as that happened to be the colour in the machine at the time, the thought is that it will have two or three buttons for configuration/menu use and possibly a warning LED under the display.

Front view of first prototype with display in place...

Click image to enlarge


Rear view showing the Arduino in position...

Click image to enlarge


Cost so far is around £6 including printer filament but there's still a lot of work to do to finish it and I currently have a LOT of projects on the go ! http://www.yorkshireoffroadclub.net/


Last edited by davew on 16th Nov 2018 12:07pm. Edited 2 times in total

Post #740807 16th Nov 2018 11:50am
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Martin
Site Admin


Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 4934

United Kingdom 2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

The Defender Td5 coolant signal is totally hopeless for detecting an overheat condition.

You either need to run something which can read the ECU's internal coolant temperature reading in degrees C, or fit a second sensor.  1988 90 Td5 NAS soft top Cool
2015 D90 XS SW Mr. Green
2006 D110 CSW (Dad's)

Nanocom, IID, Forscan and Webasto diagnostics available in North Oxfordshire

Post #740808 16th Nov 2018 11:54am
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davew



Member Since: 02 Jan 2012
Location: North Yorkshire
Posts: 880

England 1990 Defender 90 V8 Petrol PU Auto Rioja Red
Re: Plug into temperature guage to get a warning light

Martyn668 wrote:
Hi all,

What is the wire telling the gauge? HIgher voltage? Higher frequency pulses?


The temperature gauge is driven by the ECU on a TD5, it reads in the data from the coolant sensor and then converts that to a PWM output appropriate for the gauge cluster being used. There is no direct connection between the gauge and the sensor.

It's simpler to use your own sensor, as the MadMan does, although there is no technical reason why you couldn't tap off the feed into the ECU (let the TD5 ECU provide the reference voltage though so your own processor is completely passive) but if you provide your own sensor it's both easier to calibrate and you can measure it where you want to - bottom hose or top hose, you can decide if you want to monitor the engine temperature or cooling efficiency. http://www.yorkshireoffroadclub.net/

Post #740811 16th Nov 2018 12:02pm
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achuakh



Member Since: 12 Apr 2012
Location: Singapore
Posts: 130

Singapore 2002 Defender 90 Td5 SW Oslo Blue

The Td5 temperature gauge is driven by the voltage output from the ECU, not directly though.

hang on, it's not so straight forward. in the ECU there is a 3D table which has some look up points as to where to move the gauge to based on the input voltage. in the 3rd dimension of the look up table specifies 10.8v and 14v so meaning it will try to give you the right reading based on the current voltage be it non charging or running.

next, you have optimal operating temperatures which land rover specifies from 75 to 115 deg c. this is where they programmed the gauge not to move at all, so meaning it will sit slightly to the left of the middle like it usually does. this is not to scare people when they see a moving gauge towards the right. the next increment is at 118, then 120 and 127 is everything beyond (again if i recall correctly) so these are the numbers you don't even want to get near.

assuming your cooling system is working correctly, it should actually only be 86 to 95 deg and come back quickly to around 88.2 deg.

so the hottest it will get before moving the gauge is 105 deg hence when it starts to climb it goes really fast. so this is not what you want.

if you are into doing a remap, you actually can change how this responds at the same time, and i've made 88.2 right about in the middle (still a lesser tad to the left) and mine actually moves if the temp goes up slightly to 95 so i can see the gauge. yes, it does scare you if you don't know the numbers and see the gauge move.

right about from the middle of the center to right most will be 120 deg on how i did mine (haven't seen it before), so if it's there, it's probably too hot and i should pull over and check on my cooling system.

Back to your question, so if this is not something you want to do, then i guess it's easier to get a fixed temp sender (thermostat) maybe at 110 deg and put that into a T pipe which uses a separate circuit to close a blinking red LED.

If you have a nanocom one, you can set it to blink the red light at a specified temperature, solving the problem without any additional wiring and also allowing you to perform diagnostics and upload ECU maps.


Click image to enlarge
 From the land of the most expensive land rover defenders on planet earth. At 125k for a XS 110 csw and you get to own it only for 10yrs! Please find me a good reason to stay on this island.

Post #746638 20th Dec 2018 6:23pm
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