Oil temp sender faulty?

[Bob L]

I’ve finally got around to installing a water temp sensor within the oil filter housing and the on/off/on toggle switch (as used by others) to utilise the existing standard Caterham water temp gauge.  Unfortunately, no reading when I switch to oil temp, needle returns to zero.  Water temp is fine when switched.  Checked the wiring, switch and earth – all seems good.  I now suspect the sensor itself may be faulty.  I can rig a multimeter to the sensor while driving and view the reading.  Any electrical geniuses out there know what resistance measurements I should be able to view when at ambient (engine cold) and when hot.  Just want to be sure before I remove and replace.

Temp sender (water) for Caterham gauge 96 on - supplied by one of our best -RC Ltd

[Wrightpayne]

Did you use PTFE on the threads? (A no-no on engine oil systems)

The body of sensor needs to make an earth contact, which it normally does through the thing its screwed into.

(just re-read your post and you said earth been checked)

 

[ScottR400D]

Wrightpayne is correct but have you driven the car far enough? Mine takes 3-4 miles before I get a reading of any sort. 
 

 

[Wrightpayne]

Good point - its a good 10-15mins of driving before I see any significant movement on the oil temp.

Another thought - just check the resistance of the water sender cold and hot as the new one should be the same spec. I don't think you need to check it going along, just a cold measurement then one when its fully up to its normal running temperature 

[Bob L]

Thanks for your comments.  

Yes, I suspected an earth issue but there was no resistance between the sender top nut and the engine block.  No PTFE used, just a little sealant. 

Time to warm up - I thought the same, gave it 8 miles in varied traffic but when switched (periodically), the gauge drops right to zero.

Resistance of the water sender - Brilliant idea  and its very accessible.  I should I have thought of that.  Thanks.

[OldAndrewE]

I assume the senders are physically the same size thread.  If you do not get anywhere perhaps try swapping them over and see what happens

Edit: Or before you try that swap the two wires over on the senders (if they reach).  Again see what happens

[aerobod - near CYYC]

To ensure you have the right temp sender and there is continuity to earth, check the resistance to earth on both sensors with the wire removed when the car is fully cool, they should be within a few percent of each other.

[revilla]

On two brand new sensors on each of two spare engines (four sensors in total) I get between 2410 and 2470 ohms sitting in my garage at whatever the ambient temperature is today.

[Bob L]

Thanks for all your help, suggestions and raw data.

Very much appreciated.

 

Rgds, Bob