new temp gauge, doesnt seem to work Options

[7391420]

I've posted this a few times, and after trying several methods it's still not working..

-new vdo temp gauge-with the numeric readout.

-It plugs right into the old plug but it's not reading anything after driving the car for a while

-the old gauge worked (so i know the wiring is good)

-I did at the time buy a new VDO temp sensor, do I need to install this to get the gauge to work? can I remove the old one and plug this one in? or do I need to fabricate a place to plug it in and wire it up?






-

[bob174]

I went through the same thing. Two of the wires in the plug need to be reversed. If you look at the wiring diagram that came with the new gauge, and you look at the letter designations marked on the back of your old gauge, you'll see the two that need to be switched. I'm sorry I can't recall which ones they are--IIRC it's the sense and the light, the ground stays the same???

You will need to install the new sensor to make the gauge work, obviously after draining the oil. It screws right into where the same spot as the original without modification and you can use the existing wiring. Doing the sensor was the easy part! Figuring out the reversed wires took a little head scratching.

Bob

[Dave_Darling]

It should read something, even with the old sender...

Time to check some stuff. First, make sure you've got an oil temp gauge, not a head temp gauge. (They work on two very different principles!) Next, make sure that you've got +12V when the ignition is "on" at the red/white wire that plugs into the back of the gauge. Next, make sure you have a decent ground on the brown wire going to the gauge. Next, check the resistance of the wire coming from the sender. It should give you a definite resistance, though I forget the range. I think it might be about 3000 ohms when the engine is cold? It gets lower as the engine warms up.

If the resistance is infinite, the wire is unplugged or broken somewhere. If the resistance is zero, the wire is shorted to ground somewhere.

If all of that checks out, you may have a dead gauge. You can try substituting a potentiometer (variable resistor with a knob) for the sender--plug one end into the gauge and the other to a ground. The needle should move when you tweak the knob. If it doesn't, the gauge is dead.

--DD

[7391420]

Thanks for the help,

-I am replacing the temp gauge off my center console, (73 2.0l origional center cons. gauge set up) oops, I should know but, is this a head temp sensor or a oil temp sensor?


-if it's a head sensor will my new gauge then not work?

[7391420]

Bob,

were you replacing the origional temp sensor from a center console? if so, I'll follow that plan at my next oil change!

-Adam

[914ghost]

If its a regular VDO based on resistance, you can unplug and ground the wire at the sender and if the gauge pegs then its probably ok.
Also, both your sender and your guage may be fine, but they may be calibrated so differently so as not compatible. Use the parts that came with / or are meant to be used together- even parts MATCHED to each other are commonly 10% to 60% off in reading.
Its the price we pay to pay less! = mass production.
Best thing:
Get a candy thermometer and boil some water (or HEAT up some cooking oil, it gets hotter than water)-
go out to your car with the hot water or oil in a pan and the thermometer in it.
Have your sender out but wired to guage AND its housing to ground.
Plop it in the water/oil and read your gauge compared to the candy thermometer...mentally note the diff. or mark your guage. Then you always know how hot you really are!!
Its the only way to be sure....
-Bob O

[Dave_Darling]

If its a regular VDO based on resistance, you can unplug and ground the wire at the sender and if the gauge pegs then its probably ok.

D'OH! That's an awful lot easier than getting a potentiometer...

The stock temp gauge is an oil temp gauge. It does work on resistance. The stock sender will run the aftermarket gauge, but the readings will be rather wrong.

Do the checks that I mentioned above--checking for power, ground, and some kind of resistance. And then ground the "sender" connection on the gauge as Bob said. That will test out the different parts of the system.

--DD

[john rogers]

VDo temp gauges are matched to a specific sender. If the gauge is a different model that the old one and it sounds like it is then you can contact VDO, give them the number that is on the body of the gauge and the tech can tell you what sender you need. I recently had this same problem since my 4 cylinder race engine blew at the CA Speedway and the oil temp sender went flying. We tried several senders, even the one recommended by VDO and could not get accurate readings. VDO said to put a 1k pot in line with the sender wire, get the engine real warm, measure the oil temp and then adjust the 1k pot until the gauge matches the actual oil temp. Remove the 1k pot, read the resistance and add a resistor the same amount. I did this and have accurate readings now. I probable should have bought a set with the gauge and matched sender, but since the one I had was made in 1978 I wanted to keep it......You can do a search on the net for VDO USA to get their number, nice people. Good luck