Temperature Guage Question/Problems

[johnjb]

The Temp. Guage on my 70 Charger has never worked.  I grounded out the wire which connects to the send unit and the needle on the guage pegged.  I assumed this meant the connect to the guage was good.  So I replaced the sending unit.  Still does not work. Anyone seen this before or have an idea as to what the problem is?  All the other guages on the insturment panel work.

[Plumcrazy]

Assuming the engine is coming up to normal temperature, I would say you have a defective sending unit or you have a sending unit for a warning light not a gauge.

[Manfred318]

I have the same problem but none of my gauges work

[Plumcrazy]

I have the same problem but none of my gauges work

Different problem.   A bad voltage limiter for the gauges is the first thing I would check if I had that problem.
A bad circuit board is also possible.

[Manfred318]

Ive replaced the voltage limiter and circut board but still nothing happens

[johnjb]

Here is an update on the Temp guage problem.

I am getting a pulsing voltage between 0 to 5 volts from the wire which attaches to the temp sender.

I thought the voltage was suppose to osclate between 0 to 12 volts with the average around 5 volts.

So is the voltage just too low?  I check again the wire which connects to the oil pressure sender and it also swings between 0-5 volts?

Is this too low?  Sounds like the volt reg?

[Plumcrazy]

Here is an update on the Temp guage problem.

I am getting a pulsing voltage between 0 to 5 volts from the wire which attaches to the temp sender.

I thought the voltage was suppose to osclate between 0 to 12 volts with the average around 5 volts.

So is the voltage just too low?  I check again the wire which connects to the oil pressure sender and it also swings between 0-5 volts?

Is this too low?  Sounds like the volt reg?

A voltmeter is not the best thing to use to check that because it may respond to slowly to the quick voltage pulse.  Use an ordinary test light.
A bad voltage limiter would effect all the gauges not just the temperature gauge.   If the temp gauge goes to full scale when you ground the sender wire the problem is something to do with the sending unit.

[Plumcrazy]

Ive replaced the voltage limiter and circut board but still nothing happens

Have you checked for a pulsating voltage at any of the sending unit wires with a test light?

You're may to have to pull the cluster out just enough so you can do some more testing.

[Manfred318]

Ive replaced the voltage limiter and circut board but still nothing happens

Have you checked for a pulsating voltage at any of the sending unit wires with a test light?

You're may to have to pull the cluster out just enough so you can do some more testing.

I get a pulsing voltage at the sending units. what other testing should I do?

[Plumcrazy]

Ive replaced the voltage limiter and circut board but still nothing happens

Have you checked for a pulsating voltage at any of the sending unit wires with a test light?

You're may to have to pull the cluster out just enough so you can do some more testing.

I get a pulsing voltage at the sending units. what other testing should I do?

Ground the sending unit wires one by one with the key on while someone watches the gauges.   They should go to full scale fairly quickly.

[Manfred318]

Ive done that awhile back and the guages shot up quickly. They did work alittle (doesnt usually happen) this morning when I moved my car around the yard. I was showing around 5 lbs of oil pressure and an E tank of gas (which I filled up a few days ago).

[resq302]

Almost sounds like a ground problem at the dash.  Have you tried cleaning the grounding points on the dash area where your printed circut board attach or where the gauges meet?

[Manfred318]

yep tried that too, but same ole results

[Plumcrazy]

Ive done that awhile back and the guages shot up quickly. They did work alittle (doesnt usually happen) this morning when I moved my car around the yard. I was showing around 5 lbs of oil pressure and an E tank of gas (which I filled up a few days ago).

Try this.   Get a 10 ohm resistor and attach a small alligator clip on each end.
When you attach it between one of the sending unit wires and a good ground you should see this with the key on.

The fuel gauge should go to full
The oil pressure gauge should read 80 psi
The temp gauge should go to 250*

[Manfred318]

Ive done that awhile back and the guages shot up quickly. They did work alittle (doesnt usually happen) this morning when I moved my car around the yard. I was showing around 5 lbs of oil pressure and an E tank of gas (which I filled up a few days ago).

Try this.   Get a 10 ohm resistor and attach a small alligator clip on each end.
When you attach it between one of the sending unit wires and a good ground you should see this with the key on.

The fuel gauge should go to full
The oil pressure gauge should read 80 psi
The temp gauge should go to 250*

Tried and the gauges maxed out. They did decide to work a bit again today. about the same as yesterday tho.

[Plumcrazy]

Ive done that awhile back and the gauges shot up quickly. They did work alittle (doesnt usually happen) this morning when I moved my car around the yard. I was showing around 5 lbs of oil pressure and an E tank of gas (which I filled up a few days ago).

Try this.   Get a 10 ohm resistor and attach a small alligator clip on each end.
When you attach it between one of the sending unit wires and a good ground you should see this with the key on.

The fuel gauge should go to full
The oil pressure gauge should read 80 psi
The temp gauge should go to 250*

Tried and the gauges maxed out. They did decide to work a bit again today. about the same as yesterday tho.

Okay, you've eliminated the voltage limiter,circuit board,gauges and wiring as possible causes of the problem.
The only things left are bad sending units or the ground for them.

Next do this.  Run the car until it's warm enough for the temp, oil pressure and fuel gauges to be giving you a normal reading.
Then get a long wire and attach it to the battery negative terminal and the other end to each of the sending units.  Clean the metal on the units if necessary.  Let me know what each one does.

[41husk]

I changed the sending unit and the gauge worked, car overheated and the gauge did not work again, changed the unit again and the gauge is working.  Next time it goes, I may just be without a gauge.

[Manfred318]

Ive done that awhile back and the gauges shot up quickly. They did work alittle (doesnt usually happen) this morning when I moved my car around the yard. I was showing around 5 lbs of oil pressure and an E tank of gas (which I filled up a few days ago).

Try this.   Get a 10 ohm resistor and attach a small alligator clip on each end.
When you attach it between one of the sending unit wires and a good ground you should see this with the key on.

The fuel gauge should go to full
The oil pressure gauge should read 80 psi
The temp gauge should go to 250*

Tried and the gauges maxed out. They did decide to work a bit again today. about the same as yesterday tho.

Okay, you've eliminated the voltage limiter,circuit board,gauges and wiring as possible causes of the problem.
The only things left are bad sending units or the ground for them.

Next do this.  Run the car until it's warm enough for the temp, oil pressure and fuel gauges to be giving you a normal reading.
Then get a long wire and attach it to the battery negative terminal and the other end to each of the sending units.  Clean the metal on the units if necessary.  Let me know what each one does.

Ok I tried this yesterday afternoon. I hooked one end of the wire to the battery and the other directly on the unit and it had virtually no effect maybe a minute difference, not enough to realy tell though.

[Plumcrazy]

Ive done that awhile back and the gauges shot up quickly. They did work alittle (doesnt usually happen) this morning when I moved my car around the yard. I was showing around 5 lbs of oil pressure and an E tank of gas (which I filled up a few days ago).

Try this.   Get a 10 ohm resistor and attach a small alligator clip on each end.
When you attach it between one of the sending unit wires and a good ground you should see this with the key on.

The fuel gauge should go to full
The oil pressure gauge should read 80 psi
The temp gauge should go to 250*

Tried and the gauges maxed out. They did decide to work a bit again today. about the same as yesterday tho.

Okay, you've eliminated the voltage limiter,circuit board,gauges and wiring as possible causes of the problem.
The only things left are bad sending units or the ground for them.

Next do this.  Run the car until it's warm enough for the temp, oil pressure and fuel gauges to be giving you a normal reading.
Then get a long wire and attach it to the battery negative terminal and the other end to each of the sending units.  Clean the metal on the units if necessary.  Let me know what each one does.

Ok I tried this yesterday afternoon. I hooked one end of the wire to the battery and the other directly on the unit and it had virtually no effect maybe a minute difference, not enough to really tell though.

When you did the test with the 10 ohm resistor you verified that everything up to the sending units is working properly.
By attaching a wire between the sending units and the battery negative terminal you eliminated a bad ground as a possible problem.
The only things left are bad sending units.

[Manfred318]

I repalced them no to long ago but they could have been DOA, the fuel sender was replaced about a year ago with a new Chrysler one fron Year One ($$$). I will got pick up a new oil and temp one this after noon and see if that fixes the problem.

[Plumcrazy]

I repalced them no to long ago but they could have been DOA, the fuel sender was replaced about a year ago with a new Chrysler one fron Year One ($$$). I will got pick up a new oil and temp one this after noon and see if that fixes the problem.

Make sure the sending units are the ones for gauges not warning lights

[Manfred318]

I repalced them no to long ago but they could have been DOA, the fuel sender was replaced about a year ago with a new Chrysler one fron Year One ($$$). I will got pick up a new oil and temp one this after noon and see if that fixes the problem.

Make sure the sending units are the ones for gauges not warning lights

ok i will make shure of that. I do have a ? about the resistor though. Something is telling me I probably done something wrong with that. The resistor I used was out of a car and was probably the wrong thing. So my ? is could maybe send me a pic of the right thing to use and the best place to find one, because I feel as if I need to try that again before I spend the $ on new units when they may not work either. Thanks alot for all of your help too!!
--John

[mikepmcs]

You should be able to find a 10ohm resistor at Radio Shack very cheap.

[Plumcrazy]

You should be able to find a 10ohm resistor at Radio Shack very cheap.

   Make sure you test things exactly as described or you will misdiagnose the problem

[Manfred318]

You should be able to find a 10ohm resistor at Radio Shack very cheap.

   Make sure you test things exactly as described or you will misdiagnose the problem

Gotcha I picked up a pack of 5 and am gonna go check it and see what happens. Sorry for my stupidity.