Ok, I must be doing something wrong! Oil temp gauge

[LawrenceR]

I wonder if anyone can shed any light on what I am doing wrong.

I am trying to set up a switchable temperature gauge. This is what I have done and tried to do to trouble shoot.

1. Added indicator switch between oil pressure and water temp gauges

2. Fitted sender to the bottom of dry sump tank

3. Run wire from dash to sender 

4. Connect centre leg of switch to the sender input on gauge.

5. Connect original water sender input to one leg of switch

6. Connect new wire to other leg of switch.

With the switch operated the water temp still works but the new oil temp does not. 

Touble shooting with multimeter 

1. Check switch works - tick

2. Check resistance across oil temp sensor - tick

3. Check continuity on new wire run from switch to sensor - tick

4. Check continuity of system insert multimeter in circuit between water sensor input and gauge- tick

5. Check as above but with oil temp sensor input wire - fail

So my question what stupid school boy error have I done. 

Thanks 

LawrenceR

 

[SM25T]

Duplicate !

[SM25T]

If you take wire off oil temp sender and touch it to ground with oil selected and ignition on .... does gauge go to full scale. If yes .... circuit ok. Maybe too much PTFE tape on sender or tank is maybe not earthed ?

[LawrenceR]

I have checked earth for the tank and is ok. I have also checked the sensor earth and that is good as well.

I will check for FSD in the morning 

thanks 

[SM25T]

Try swapping sender input wires at the selector switch. It will be something silly. Crimp not contacting cable core .... poor earth, faulty switch ... wiring error twixt switch and gauge

[Richard Price]

Oil temperature normally lags coolant temperature very significantly.

I never get oil temperature to match coolant temperature when driving on the road.

I'd check the resistance of both senders with everything cold, and then again when both coolant and oil are hot (not just warm)

[Ian B]

One observation: most people use a Main/Dip switch, rather than an Indicator switch, as it doesn't have a centre 'off' position 

Are you def using the 'wiper' connection of the switch to the gauge, and not one of the other 'contacts', as that could cause the effect you're seeing? (asuming everything is up to temp as above).

[SM25T]

I use an indicator switch so there is a definite disconnection between sensors. It does take 10-15 minutes of driving before the oil temperature in my Apollo tank starts to register. I keep the revs below 4000 until the oil gets to 50C.

[Ian B]

Main / Dip switches are break before make Ian  

[Jonathan Kay]

Try swapping sender input wires at the selector switch. It will be something silly. 

Mostly this. But, since you're already measuring resistance at the oil temperature sender, what is it hot and cold... and is it the same when measured at the gauge side of the switch (and thus including the contacts and wires) as when measured at the sender?

Jonathan

[Paul Deslandes]

It's most likely due to the lag in the oil temperature but try connecting the oil temp sender directly to the gauge, bypassing the switch.

[LawrenceR]

Sorted now, thanks all. 

 

On the connection block, on the back of the gauge, the terminals were marked up S, +, and, earth. I wrongly assumed the S was sender and + live. In actual fact the + is the sender and S the live.

I had not noticed the two wire into the S. One is power to this gauge and the other is power to the next gauge. 

I had connected live to the one leg of the switch then the centre leg back to live, hence it worked with the water temp but not with oil as there was no power and the sensor return was connect to the live terminal of the gauge via the switch.

swapped over and all working as it should.

 

thanks again all

 

[Jonathan Kay]

Well done.

Jonathan