Topic: Temperature Gauge problem ...

[jphillips3333]

Stopped working some time ago.  Decided to take a look recently.

Symptoms;
No reading whatsoever.

Actions;
Turned the key and grounded the green wire - guage went to maximum reading.  Took the ground off, back to nothing.
Replaced the sending unit.  Nothing.

Does the sending unit require a ground wire?   It's threaded into the aluminum intake assembly ...issues there?  There's no option to thread into the heads.
Could the sending unit be bad .. best way to test it?   

[ta78w72]

It's the sender.  Replace it.  The sender wire is working as it should....that's why you got the correct gauge readings with grounding and ungrounding that wire.

Usually it's in the head between the first and third cylinder.....but if you have a 403 it might be different.

[Rick]

Also, when you replace it, don't use teflon tape.  You want a good ground connection between the sending unit and the block, and tape just screws that up.

I don't know of a convenient way to test a sending unit in the car -- unless you use one of those laser aimed remote thermometers.  But it sounds like yours is shot.

[ta6point6]

You could also check the circuit board in the back of the speedo/tach cluster if the other things check out fine. I am cheap so I just ran a jumper wire on the back of the circuit board to get mine working again. I cant see spending 70.00 when a .05 piece of wire will do the job. If you pull the cluster it is usually pretty obvious where the break is in the circuit board.

[jphillips3333]

Well there's my problem.

I did replace the sending unit but due to being overly sensitive to fluid leaks, I used teflon tape.  See, I've a bachelor's in mechanical engineering .... the sparky stuff is ALWAYS an afterthought. 

Let me back that out and see how it goes ....

[ta78w72]

Don't waste your time.  That sender is grounded.  Check it with an ohm meter.  If it wasn't grounded, the gauge would register far left.  Since you're registering far right, the sender is bad, or you may have gauges incorrect for your year and the sender may have the wrong resistance for the gauge.

If you have newer type gauges with the symbols rather than the words with a sender that was designed for the word gauge.....you get a high reading.

[jphillips3333]

Sender has 11+ volts with key on.   Positive to the connector.  Negative to the sender base and then to the intake.

This is a NEW sending unit.  I get no reading - it's always on 0, far LEFT (like California).

Background;
I tried two old sending units - one that was laying around, the other from the 6X heads.  Both didn't register any temperature.
Bought the NEW sender - nothing.
All three have gone in the intake - no location for in the heads for the sender.
All three have had the TEFLON tape on ... I may yank that in a minute.

The guage is OEM, worked prior to the head swap.
The guage responds to grounding off the connector with the key on - more than max temperature reading.  Clicking sound.

[ta78w72]

I may have misread your original post.  Somehow I got the idea that your gauge registered way hot all the time.  If you do indeed get nothing....Rick could be right about the teflon tape.  However, I've used teflon tape and still had the gauge work correctly.

The test to see if the sender is grounded would be to select Ohms on the multimeter.  Put one lead on the head of the sender and the other on the intake.  If you get no resistance, you've got ground.  If it indicates an open circuit...well Rick would be right that the teflon tape caused you to lose ground.  If you've got that sender on the intake, then you can remove it without draining the radiator down.  In the head, you've got to drain the radiator, otherwise coolant gushes out.

You're getting  the correct amount of voltage for that green wire.

[jphillips3333]

No teflon now, still no dice.

I'm going to post a shot of the wiring at the forward end of the harness running along the driver's side intake manifold.  The wire I'm using is dark, dark green if it's any color.  It does effect the voltmeter when grounded and power/key on.

Now, there is a lighter green that's bundled with the red wire that connects at the alternator.  That's got me scratching my head but the darker wire has the right connector for the sender.   

[ta78w72]

Your wiring is OK.  If you went through grounding and ungrounding that green wire and the gauge reacted properly, the wiring isn't the issue. 

What does the gauge do when the wire is connected and you turn the key on?

[jphillips3333]

Nada ... sits there.

[ta78w72]

Does it sit at the cold or hot position?

Did you check the sender connectivity from the head of the sender with the intake?  If you're sitting on the cold end, the sender isn't grounded.  Try running a ground strap from the base of the sender to the block and see if that gives you a reading (not from the sender terminal).  If you're sitting at the high end, the sender is the wrong ohm spec for the gauge.

[jphillips3333]

Cold - never budges when the key is turned.  Only movement is when the wire is grounded & the key is on.

[ta78w72]

Cold - never budges when the key is turned.  Only movement is when the wire is grounded & the key is on.

Then for some reason the sender isn't grounded.  Try running a ground strap. Also, use your ohm meter from the nut part of the sender for one lead and the other to the block to see if the sender grounds to the block.

[jphillips3333]

Sounds like it to me too.  I'll see if I can solder/wind on a wire at the threads at the sender then over to the heads/block ...battery - somewhere with a consistent ground.