Dual Water Temp Gauges - issue?

[despot67]

Well as I dont smoke I have removed the ashtray out of the Terrano and made a bracket and fitted a blue led temp gauge (52mm in black) as this leaves me room for a Voltage gauge to be mounted next to it.

I have ran the power in and an extra wire from the existing sensor next to the thermostat but the issue is it doesn't show the temp until I switch the engine off - it just shows 40 degrees whilst running. Is this because Im using the existing sensor or should I have used the one with the gauge instead as I wanted to keep both live in the vehicle?

Also out of interest what is the sensor with two wires adjacent to it in the engine for?

 

[Paff]

Pictures...

 

[rustic]

...I have ran the power in and an extra wire from the existing sensor next to the thermostat but the issue is it doesn't show the temp until I switch the engine off - it just shows 40 degrees whilst running. Is this because Im using the existing sensor or should I have used the one with the gauge instead as I wanted to keep both live in the vehicle?

Also out of interest what is the sensor with two wires adjacent to it in the engine for?

The existing temperature sensor is quite happy running the temperature gauge in the car.
This is because the car guage is wired to 12 volts in the meter, and the meter wire requires a variable resistor connected to earth to allow current to flow, which is proportional to temperature. Thus adding a second meter will also see this voltage from the other meter, hence it appears to work when the other meter is switched off ie ignition off.
So ideally you need the other sensor, you could position this cable tied to a hose, and place some insulation around it, or drill a hole somewhere and install it... not as easy as you think lol. Or mount it against the cylinder head, but again you will need some insulation over it, as the air will over cool it.
I guess you can fit an inline threaded hole, that you basically cut a hose and fit a length of correctly sized tube in, with the sensor pre mounted.
See ebay, search "temperature sensor pipe" and you will see what I mean.

On the Td, there are three temperature sensors, one for the gauge, one for the ECU and one for the glow plug circuit.
I have it written down somewhere which is which...:doh
Rustic

 

[despot67]

The existing temperature sensor is quite happy running the temperature gauge in the car.
This is because the car guage is wired to 12 volts in the meter, and the meter wire requires a variable resistor connected to earth to allow current to flow, which is proportional to temperature. Thus adding a second meter will also see this voltage from the other meter, hence it appears to work when the other meter is switched off ie ignition off.
So ideally you need the other sensor, you could position this cable tied to a hose, and place some insulation around it, or drill a hole somewhere and install it... not as easy as you think lol. Or mount it against the cylinder head, but again you will need some insulation over it, as the air will over cool it.
I guess you can fit an inline threaded hole, that you basically cut a hose and fit a length of correctly sized tube in, with the sensor pre mounted.
See ebay, search "temperature sensor pipe" and you will see what I mean.

On the Td, there are three temperature sensors, one for the gauge, one for the ECU and one for the glow plug circuit.
I have it written down somewhere which is which...:doh
Rustic

So not as easy as Id hoped, I don't trust the existing sensors hence wanting a nice accurate lcd model - might just place it somewhere on the head to register engine temperature unless as you advise I can split a pipe somewhere and put a metal part in between with the sensor threaded into the casing?

 

[rustic]

So not as easy as Id hoped, I don't trust the existing sensors hence wanting a nice accurate lcd model - might just place it somewhere on the head to register engine temperature unless as you advise I can split a pipe somewhere and put a metal part in between with the sensor threaded into the casing?

If you mount it on say the top rad hose, then it might only register when the thermostat starts to open, so nothing for half an hour and then an instant 82C

Also a hose connection will not give you any warning of any coolant loss and an over heating engine because of no water. So somewhere on the engine metal work that is water cooled is best.

For my outboard engine, I bought a thermistor with exactly the same temperature characteristic as the brass sensor that came with the meter, this I epoxied to the side of the thermostat housing, that was on the cylinder head.
It works great, and gives a pre warning of a blocked water inlet, or a failed water pump impeller.
The problem is, finding the right thermistor, this can be done with an ohm meter, and an accurate thermometer, and take various readings at set temperatures.

Edit... have a look here, yours is probably a negative or NTC version.

Hope it helps,http://www.ni.com/tutorial/7112/en/


Rustic

 

[despot67]

If you mount it on say the top rad hose, then it might only register when the thermostat starts to open, so nothing for half an hour and then an instant 82C

Also a hose connection will not give you any warning of any coolant loss and an over heating engine because of no water. So somewhere on the engine metal work that is water cooled is best.

For my outboard engine, I bought a thermistor with exactly the same temperature characteristic as the brass sensor that came with the meter, this I epoxied to the side of the thermostat housing, that was on the cylinder head.
It works great, and gives a pre warning of a blocked water inlet, or a failed water pump impeller.
The problem is, finding the right thermistor, this can be done with an ohm meter, and an accurate thermometer, and take various readings at set temperatures.

Edit... have a look here, yours is probably a negative or NTC version.

Hope it helps,http://www.ni.com/tutorial/7112/en/


Rustic

According to the link the thermistors have multiple connectors and you use these to test them but this comes with a single terminal connector like the one in the engine block?

I might connect it to the actual cylinder head like you advised and see what it shows? it wont hurt if I try numerous locations till IM happy as I admit it is only for peace of mind with relation to engine temps.