Water Temperature sensor Ohm value?

[CHB]

any one knows the proper ohm value for 3T-C EFI? i got 2 of them, both give me different values.
one is 30.3ohm and the other one is 70ohm..
which one is a working unit?
can an engine started without the signal from water temperature sensor?

[Cool1]

The engine should start without the sensor. Also remember that the resistance will change depending on the temp of the sensor. This is why you will not get the same values been the two.
You could try putting both in some warm water for a while and then retest them.

[The Witzl]

Please do a google search on "NTC thermistor" or "negative temperature co-efficient thermistor"

... it will explain what is basic electronic principles and not worth the spoon of feeding.

[Cool1]

Man he asked a good technicial question. Why tell him to do a google search when this section is here to ask the types of question he asked?

[Sigmeister]

What do you mean "The Ohm Value"? As in Max and Min settings? And is this to match up with another guage or something? You can ground the signal wire, that should tell you one? As Cool1 said, it will be different depending in the temperature.

[The Witzl]

well.... cos.....

.... ok im lazy! But that is how i find everything out! Google answers ALL my questions, i only come here when google can't help anymore....


The bigger story..

The water temp sensor is basically a NTC Thermistor encased inside the metal housing that bolts into your engine where there is coolant present (eg. thermostat housing, etc).

An NTC thermistor is a device that provides a variable resistance based upon the temperature of it's body. This means that it will give two different resistance measurements (ohms is the unit of resistance) at two different temperatures.

Here's an example of the resistance vs temperature curve of a common NTC Thermistor.



What it is basically showing is that as the temperature of the thermistor increases, the resistance (or ohms) you measure will decrease.
This decrease is exponential, which is shown by the graph being curved rather than a straight line.... meaning that when the temperatures are low, for every degC of temp change the resistance change is rather big - but when the temperatures are higher, the changes in resistance for every degC of temp change are comparitively small.... which means that in the higher end of this device's temperature range, it measures very accurately (exactly what you want in an engine!)


As for what the "typical" measurement would be for your 3T water temp sensor - unfortunately i wouldnt know without knowing the p/n of the NTC thermistor inside.
But performing a test of putting it in water that you slowly heat up on the stove, and measuring the resistance as the temperature rises, will show if it is working correctly or not.

I hope i've helped now




(happy shane?? )

[Cool1]

(happy shane?? )

I'm never happy! I'm an angry man.

Sigmeister, I assume he is talking about the temp sensor for the ecu, not for a guage.

[Sigmeister]

Sigmeister, I assume he is talking about the temp sensor for the ecu, not for a guage.

Oops
Sorry about that.

[CHB]

I'm never happy! I'm an angry man.

Sigmeister, I assume he is talking about the temp sensor for the ecu, not for a guage.

yape, i'm refering to the sensor to the ECU. one side is connected to chassis ground while the other end is from the ECU.

[The Witzl]

yape, i'm refering to the sensor to the ECU. one side is connected to chassis ground while the other end is from the ECU.

correct... and it varies resistance from the ECU wire to ground, depending on temperature.

So did my post above help?

[CHB]

one thing, i'm using Datsun L28 ECU, so what i m refering to the wiring diagram is "Cylinder head temperature sensor", so i assume it refer to water temperature for ECU. am i right?

[CrUZida]

Err, you need to use the correct sensors for the ecu dude.

Unless by random chance the 3T-C sensors are the same as the L28 sensors, you will need to get an L28 sensor, or have the L28 ecu reprogrammed to suit the 3T-C sensor.

[The Witzl]

one thing, i'm using Datsun L28 ECU, so what i m refering to the wiring diagram is "Cylinder head temperature sensor", so i assume it refer to water temperature for ECU. am i right?

this screams of dodginess...... i'm now leaving this thread....

[CHB]

ok.. able to get my car idle smoothly today after done some tricks on the sensors.. thanks for the informations mates.. cheers..

[RA23]

..... which means that in the higher end of this device's temperature range, it measures very accurately (exactly what you want in an engine!)

I agree with everything The Witzl said, except for the above statement.

The accuracy drops with increasing temperature, because the ECU is measuring the resistance (actually current at given voltage or voltage at given current) and calculates the temperature from that.

Looking at the NTC graph:

At low temperatures the tempature inaccuraccy for a given resistance measurement error is rather small (because of steep gradient of graph).

At high temperatures the tempature inaccuraccy for a given resistance measurement error is high (because of very flat gradient of graph).

So the higher the temperature the less accurate the temperature measurement.