Dual use of CLT sensor

[MG David]

My MGB has an electrical temperature guage. I would like to use the existing sensor for both the temperature guage and for MS. The spec of the sensor is known so setting it up in MS is not a problem. The temperature guage is fed from a voltage stabaliser with approx 10V.

Will having the guage and MS using the same sensor cause any problem?

Do I need to use an extra diode in the MS wire to stop the voltage from the guage going back into the MS unit?

I have seen cars with a hole drilled in the head for a second sensor but I would like to avoid that. From my understanding of what the CLT sensor is for I believe putting the sensor the radiator side of the thermostat would would be a mistake.

[SymTech Laboratories]

You can share a temperature sensor between MS and another device as long as the other device uses a fixed bias resistor and a 5V voltage reference. Can you clarify what you mean by "the temperature gauge is fed from a voltage stabiliser with approx 10V"? Do you mean the gauge or the sensor?

Keep in mind that calibrating an MS1 ECU for "non-standard" temperature sensors is a little tricky (it's much simpler with MS2 or MS3).

[MG David]

The live voltage in the car is a nominal 12v but when the altenator is running the voltage is generally higher. So the live current goes through a bi-metalic voltage stabaliser on its way to certain electro mechanical gauges including the temperature guage. The stabaliser effectivly operates by switching the supply on and off. The effective average output of the stabaliser is 10v. The the wire from the guage then goes to the thermosistor type sensor were the current then passes to earth.

MS uses a thermosistor passing to earth type of sensor (although the standard GM ones have 2 wires one of them is an earth wire) so I was hoping I might be able to share the sensor between MS and the temp guage even though MS puts out a 5v reference and the temp guage puts out a 10v reference.

[Matt Cramer]

I've got a Dodge Dart, and there's a reason I advised Mopar owners not to try splitting the signal with the stock gauges. I'm not sure if MGs are the same way, but here's what I've seen on Mopars. A lot of thermal gauges have very low resistance and are current based. If that's the case, it is pretty much impossible to share the sensor. So you'd need to measure the resistance of the gauge and make sure it's in the same ballpark as the sensor's resistance. If you come up with something like 5 ohms, forget using this gauge. Not going to get a voltage range you can work with.

Next problem - which Mopars don't have; they run 5 volt gauges - is that you are running your gauge at a nominal 10 volts. You'd need a buffer and a voltage divider to bring it down to the 5 volt range.

Final issue is the pulse width modulated voltage "regulation." The Mopar regulators pulse on and off at around 1 hertz. So you'd need a huge low pass filter to get the ripple out of the signal. Luckily coolant temperature doesn't change that much.

[MG David]

OK I think I will keep it simple and add and additional sensor for MS.

[Marek]

Dear David,

I have done something similar for a 0-50k sender but the other way around.
See http://www.jag-lovers.org/snaps/snap_vi ... 1325761899
and http://forums.jag-lovers.org/av.php?1505538n60
You will have to alter the circuit quite substantially as your sender will be about 800ohms(cold) to 10ohms(hot), but the principle is the same.

You will also likely need to change out the 10v bimetallic regulator for a 7810, otherwise your electronics will see a rapidly fluctuataing supply of 12v and 0v, average 10v.
See http://www.jag-lovers.org/snaps/snap_vi ... 1287914415

Your sender and gauge have 10v across them always, but the split is 2.5v across the gauge and 7.5v across the sender when cold versus 7.5v across the gauge and 2.5v across the sender when hot, so that's what you have to reconcile with MS.

kind regards
Marek

[woh]

I have done this on an MGB and works great. The only disadvantage is that you loose resolution when the temperature is very cold. (below 0F)

As discussed above.
Two difficulties; 1. the voltage is too high for MS, and the voltage is a series of pulses.

1. replace the voltage regulator with an electronic version
2. Divide the output voltage from the sensor by two and remove the bias resistor in MS

See here:
http://home.comcast.net/~whaussmann/wmg ... ameset.htm

[stevemgbgt]

Cant remeber where I got it from but I fitted an adapter with a takeoff under the thermostat housing and fitted a rover temp sensor in that and it seems to work well.Steve

[James]

As some additional information, which is slightly useless to you, if your MS has a PWM output you can use this to drive the gauge.

I have this on my Triumph and calibrated the gauge to set temperatures.

[MG David]

Thanks for the replies.
Werner I had visited your site in the past but had since forgoten about it. It was good to have another look.

I now have a plan of action. As I am only using the MS for ignition to start with I will firstly not connect up a temperature signal so there is no warm up ignition trim. Once the system is working I will progress to a sandwich plate as James describes. Provided I become more confident in my use of the system and electronics skills I may move on to a method for dual use of the same sensor as the guage.

James, is there any reason why you used a Rover sensor? Do they provide the same output as the GM/Vauxhall ones that are the MS default?

[James]

I used the Rover one because it has the same 5/8 thread as the Triumph pump housing — so no need for adapters or additional holes.

It's the same calibration as one of the Bosch sensors I think — forgot which one.

The details are available somewhere online if you google the part number (on a Lucas parts list)

[bobtooke]

On my MG Midget I put a second sensor (from a rover 820) in the thermostat housing on the rad side, then drilled a 2mm hole in the stat under the sensor which give a nice steady temp feed at all times. Not a bad idea all round because it also avoids hot spots in the head during warm up.