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Discussion Starter · #1 ·
Got a 64 Galaxie 390 4V and the temp guage isn't working. When sender wire is touched to block, the guage responds but after replacing the sender twice I am at a loss. I put in a new fuel sender and that guage is right on so I would not think there is a problem with the constant voltage regulator for the guages. Any ideas?
 

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Just a thought, but if you are wrapping the threads of the sender with teflon tape then you may not have a good ground for the sender.

Could also just be a bad sender even if they are new. Seen it happen before with the overseas made junk.
 

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+1 on the tape. Also, there should be a ground strap or wire from the rear engine area (usually the head, block, or bellhousing bolt) to the firewall that is specifically to ensure a good ground for the instruments. Make sure it's there, clean, and tight.

List the brand and part number so we can verify you're getting the right part from the counter guys.

David
 

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Could be that you're a bit of a motard if you're not paying attention to the fact that the sender unit is a link to Ground and that it's NOT getting grounded in the threads like the boy's have already said twice.

Of course, it's only been ONE day, so I do have to cut you some slack, so I don't think you can get TWO bad senders in a row, one on occasion sure but not two normally, so that leaves us with the ground.... Is your INTAKE grounded with a good clean ground wire to the firewall? And I recommend NOT using an intake hold down bolt for the ground wire, there are MANY other bolt holes that are available.
 

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Discussion Starter · #7 ·
No not spam, I just had too much other stuff to do. I put the sender wire to the brass nut and the guage responds. This is the second sender I got from Obsolete Ford Parts so I thought it would be a good one. Hate to keep buying senders. Is there a way to test the sender with ohm meter?
 

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The way the gauge works is that it get's + from the cluster, and the Ground comes from the mercury switch inside the sending unit. The Ground is where the brass touches the threads, then as the car HEATS UP, the mercury inside expands thus causing the internal rheostat to decrease in resistance thus giving current flow to the gauge heating the internal gauge coil and moving the needle in the dash correspondingly.

What exactly makes you think that your gauge DON'T work with the new sending unit?
 

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If the gauge is right on with the new sender, maybe use the new sender?
LOL.... Pay attention Putts ...
Two totally different sending units. Fuel & temp.... ;)
 

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Discussion Starter · #10 ·
Well, long story- Bought the car with none of the guages working, I ordered a new gas tank, oil pressure and temp senders. Oil light works great, fuel guage is accurate but temp guage doesn't move at all from a cold start to full running temp. I touched the sending wire to block and the guage moved up. I thought it was a bad sender so called Obsolete Ford and they sent me another one. It doesn't show any movement either, but if I touch the wire to the brass sender housing the guage moves up. So that means I have a good ground to the manifold. I also added a chassis ground to the battery to make sure that was good. I can only deduce that the sender isn't responding. I've changed more than a handful of these over the years and never run into this.
 

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Well, long story- I can only deduce that the sender isn't responding. I've changed more than a handful of these over the years and never run into this.
I have with master cylinders and with alternators and with parking lights. Never with a temp gauge. I say get a warranty replacement. It's grounded well by your test proof, therefore the insides are not working, and it too needs replaced.
 

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... but if I touch the wire to the brass sender housing the guage moves up. ...
The gauge should not just 'move up'. It should peg hard to the max temp side of the gauge. If any less than that, you still have a ground, wiring, or gauge issue - or the wrong sender. You never did list the part you got, so I can't confirm it's the right one. Still, you can test yours with an ohm meter in hot water. Roughly 10 ohms at "COLD" and about 73 ohms at full scale. It is important (due to the different senders Ford used) that the resistance slope in-between is smooth. It will not be linear, but the resistance should not 'step' at any point.

David
 

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you can test yours with an ohm meter in hot water. Roughly 10 ohms at "COLD" and about 73 ohms at full scale.David
See Lars, I am not the only one that gets the fuel and temp senders mixed up!
 

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You're right, Putts - I said it backwards. Also, different years will have different start (cold) ohms. Given that, perhaps the better diagnostic would be to see 40 ohms at 180°F with any of them. Lots of ohms COLD, not many HOT, and 40Ω at 180°F. This would avoid the differences between years of the full-scale ohm range. Don't forget, your temp gauge guts are identical to your fuel gauge guts. Only the face is printed differently. A reading of 40Ω from your fuel sender is also about 1/2 tank.

David
 
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