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  Temp Gauge Inop (let's try this again)

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Author Topic:   Temp Gauge Inop (let's try this again)
Robert K
Gearhead

Posts: 476
From: Nashville, TN
Registered: Apr 2000

posted 12-10-2001 06:06 PM     Click Here to See the Profile for Robert K   Click Here to Email Robert K     Edit/Delete Message   Reply w/Quote
My temp gauge on the 65 is on cold all the time (even after the car overheated). I have replaced the sending unit and the instrument voltage regulator. What else could be causing the problem ? Can I swap out the stock gauge for an aftermarket one ?
Is there a way to test the gauge ?
My fuel gauge isn't working either. It's always at least + 1/4 tank off of what the real reading should be. I don't think the 2 problems are related but then again....
Any ideas ?

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67convertible 289/auto
65fastback 302/4sp

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franklin
Gearhead

Posts: 128
From: VA
Registered: Nov 2000

posted 12-10-2001 06:23 PM     Click Here to See the Profile for franklin     Edit/Delete Message   Reply w/Quote
You should be able to take the wire off the temp sending unit and with the key on, the guage should read all the way one way (can't remember if it's hot or cold). Then take the wire and touch it to a good ground like the engine block, and the guage should read all the way opposite from the first test. This will test the guage and related wiring. You can test your gas guage like this too, by taking the wire off the tank, and then grounding the wire from the tank, and it will react like the temp guage, giving full scale readings for both situations.

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richard bohm
Gearhead

Posts: 373
From: tucson,az-luray,va
Registered: May 2001

posted 12-10-2001 06:24 PM     Click Here to See the Profile for richard bohm   Click Here to Email richard bohm     Edit/Delete Message   Reply w/Quote
check for a bad ground or no ground strap from the engine to the body. also check continuity from sender to gauge, and check for power leaving the ivr going to the gauge. if you have good grounds, power to the gauge, and continuity from the gauge to the sending unit, then you likely have a bad gauge.

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67 Fastback
Gearhead

Posts: 679
From: Beaverton, Oregon
Registered: Aug 99

posted 12-10-2001 08:46 PM     Click Here to See the Profile for 67 Fastback   Click Here to Email 67 Fastback     Edit/Delete Message   Reply w/Quote
You might also try swapping the lead (from the plug on each) with the oil sending unit. If the oil sending unit then works (on the temp gauge) it shows it is probably the temp sensor. New ones can be bad at times.

If it does not work in that configuration (on the oil sending unit) it is more likely in the wire/circuit of the temp gauge. I hope this makes sense).

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Jerry
www.67Fastback.com
"The danger in communication is the illusion that it has been accomplished."
G.B. Shaw

[This message has been edited by 67 Fastback (edited 12-10-2001).]

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Boss Hoss
Gearhead

Posts: 222
From: Georgia
Registered: Mar 2001

posted 12-10-2001 09:33 PM     Click Here to See the Profile for Boss Hoss   Click Here to Email Boss Hoss     Edit/Delete Message   Reply w/Quote
All I can say is, all kinds of things were not working on my Mustang's dash until I decided to just replace the entire under-dash wiring. The wiring harness was quite expen$ive but it made a big difference. I now have my heater control back, plus all of my dash lights and my shifter indicator light! Yay!

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*andy* ([email protected])

also known as...***Boss Hoss***

*1965 Mustang 289 coupe*
*1996 Mustang GT coupe*

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RonnieT
Gearhead

Posts: 469
From: Port Allen, La. 70767
Registered: Jun 99

posted 12-11-2001 10:12 PM     Click Here to See the Profile for RonnieT   Click Here to Email RonnieT     Edit/Delete Message   Reply w/Quote
Robert,

As Franklin said try grounding the wire at the sending unit to the block, the gauge should go full scale when grounded (all gauges will when you ground them). If it goes full scale you have a bad sending unit or did not use the conductive thread sealant when installing the new sending unit. If it does not go full scale try running a jumper wire to the neg. terminal of the battery , if it goes full scale you have a bad ground to the block, if it does not move it is either the gauge or the wiring.

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Ronnie
69 mach1 351W-4V
70 Torino GT 351C-4v with a "shaker"
Mustangs and More Member #23

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Robert K
Gearhead

Posts: 476
From: Nashville, TN
Registered: Apr 2000

posted 12-12-2001 08:11 AM     Click Here to See the Profile for Robert K   Click Here to Email Robert K     Edit/Delete Message   Reply w/Quote
OK, now I've got several things to try. I'm going to work on it tonight and let everyone know what I find tomorrow. Thanks for everyone's replies.

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67convertible 289/auto
65fastback 302/4sp

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Robert K
Gearhead

Posts: 476
From: Nashville, TN
Registered: Apr 2000

posted 12-13-2001 08:42 AM     Click Here to See the Profile for Robert K   Click Here to Email Robert K     Edit/Delete Message   Reply w/Quote
I didn't get a chance to do much but I did check the temp gauge with the feed wire grounded to the block and it pegs the gauge to the 'Hot' side with the ignition on. With the ignition on and the feed wire disconnected from the sending unit (and not grounded) the temp gauge doesn't do anything just stays at the cold mark. Does this mean it's not the gauge ?

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67convertible 289/auto
65fastback 302/4sp

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lyle29464
Gearhead

Posts: 718
From: Mt. Pleasant S.C.
Registered: Mar 2000

posted 12-13-2001 09:39 AM     Click Here to See the Profile for lyle29464   Click Here to Email lyle29464     Edit/Delete Message   Reply w/Quote
That means it's the sending unit.

[This message has been edited by lyle29464 (edited 12-13-2001).]

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Robert K
Gearhead

Posts: 476
From: Nashville, TN
Registered: Apr 2000

posted 12-13-2001 09:44 AM     Click Here to See the Profile for Robert K   Click Here to Email Robert K     Edit/Delete Message   Reply w/Quote
The sending unit is brand new. I remember seeing a post saying to use a special conductive sealer on the sending unit.
I used teflon tape but no conductive sealer. Could that be the problem ?

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67convertible 289/auto
65fastback 302/4sp

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lyle29464
Gearhead

Posts: 718
From: Mt. Pleasant S.C.
Registered: Mar 2000

posted 12-13-2001 09:49 AM     Click Here to See the Profile for lyle29464   Click Here to Email lyle29464     Edit/Delete Message   Reply w/Quote
If you ground the case of the sending unit (not the post where the wire hooks) to the block and the guage works then the tape you put on the sending unit is keeping the current from going to ground. Remove the tape or get the right kind. If you ground the sending unit case and the guage does not work. It's the sending unit.

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Robert K
Gearhead

Posts: 476
From: Nashville, TN
Registered: Apr 2000

posted 12-14-2001 08:33 AM     Click Here to See the Profile for Robert K   Click Here to Email Robert K     Edit/Delete Message   Reply w/Quote
I thought I had put teflon tape on the sending unit but it turns out I did not.
From all of the above tests I've run. It sure looks like it's the sending unit even though it's brand new. I'm wondering now if I bought the correct unit. I've got an aftermarket intake that takes the larger fitting for the sending unit as opposed to the small stock fitting of the original 65-66 type. Should I buy the original type/size sending unit and then use an adapter to make it fit ? Is there a way to test the sending unit itself ?

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67convertible 289/auto
65fastback 302/4sp

[This message has been edited by Robert K (edited 12-14-2001).]

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franklin
Gearhead

Posts: 128
From: VA
Registered: Nov 2000

posted 12-14-2001 01:19 PM     Click Here to See the Profile for franklin     Edit/Delete Message   Reply w/Quote
To be safe, I would get the correct sending unit for the guage unit you have (65-66). Then go to the hardware store and get a brass hex bushing. These are just pipe threads, nothing special. Make sure you use a socket to install the bushing, if you install it into the manifold first. If you use a wrench, and the bushing has a pretty thin wall, a wrench can collapse it a little and make it out of round, and make the sending unit hard to get in.

[This message has been edited by franklin (edited 12-14-2001).]

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Boss Hoss
Gearhead

Posts: 222
From: Georgia
Registered: Mar 2001

posted 12-14-2001 01:21 PM     Click Here to See the Profile for Boss Hoss   Click Here to Email Boss Hoss     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Robert K:
I've got an aftermarket intake that takes the larger fitting for the sending unit as opposed to the small stock fitting of the original 65-66 type.

From what I understand, the smaller temp sending unit is on the '65 cars only. In 1966 they switched over to the larger sending unit. As for using an adapter to make the larger sending unit hole smaller for the small '65 style sending unit, it is possible, but I don't know how to do it other than giving the intake to a machine shop so they can do it.

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*andy* ([email protected])

also known as...***Boss Hoss***

*1965 Mustang 289 coupe*
*1996 Mustang GT coupe*

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Robert K
Gearhead

Posts: 476
From: Nashville, TN
Registered: Apr 2000

posted 12-14-2001 02:15 PM     Click Here to See the Profile for Robert K   Click Here to Email Robert K     Edit/Delete Message   Reply w/Quote
I can find the adaptor to make it work. I might even have one laying around the garage.
My question was does the fact that I'm not using the exact type of sending unit for that particular gauge/car (65-66) have anything to do with the temp gauge not working. I would think that the only difference would be size but now I'm not so sure. The resistance may be different from unit to unit and maybe the output from this unit is not compatible with my gauge. I don't know. It just looks like it's the sending unit and I want to make sure I replace it with the one that will work.

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67convertible 289/auto
65fastback 302/4sp

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