Temp gauge question
 

What does it mean when your temp gauge needle goes all of the way to the right in a matter of 60 seconds? This is on a new sending unit too.
Is that a bad ground? I've heard that teflon tape can mess up the readings. Any possibility of this?

Sounds like the wrong sending unit. If it's shorted(green wire) it goes over real fast. If you had a ground problem it would not go over at all. The connection on the sending unit should look like the head of a nail.

No help here but I have the same problem with my 69 350. When I bought the truck it had no temp sending unit at all. I went to napa to get a new sending unit, they had one listed for a 69 C10 with a 350 so I bought it. Now the gauge moves all the way to the right before the engine is completely warmed up. I'm assuming my 350 is not the original engine, I know the truck originally had a manual transmission with a floor shifter. I guess we could try getting a sending unit for a 6 cylinder or big block and see if that works.

oh yeah, my sending unit connector does look like the head of a nail...

It's the right sender...I'm positive about that. It has the end that looks like a nail head. I think there is a short in the wire somewhere. I might disconnect the printed circuit from the gage and bypass the green wire all of the way to the sender. If it works, then there is a short in the green wire somewhere. That wouldn't be surprising knowing the wiring on this truck.
Thanks for the help. This is the only gauge that isn't working right now. I got my new factory tach in and I was finally able to get the fuel gauge working. Almost there!
Thanks,
Josh

Does the guage tach out when the ignition switch is turned on with the engine turned off?
If so, unplug the green wire (ignition switch still on) and see if the guage drops. If so, replace the sender. If not, continue.
Follow green wire to bulk head, actually inspect all of the wire looking for cuts, corrosion, butn marks, or obviously, seperation. If so, repair and check...if not....
Find where the green wire goes on inside of firewall. I'm sure it runs to a fuse, and then into the main under dash harness. Inspect and check the wire all the way to the insterment panel plug. If damaged, repair and check. If not...
Remove insterment panel. Obtain a digital multimeter. A cheap one can be had at sears for about 50 bucks. Decent ones at just over 100 dollars. Look at the plug, and determine what pin (for lack of a better description) the temp wire is, and see which circuit it follows on the circuit board. Follow that circuit looking for obviouse burns, tears or any other visable breaks. If damage found, repair and check, if not...
Get the multimeter, place the selector on ohms, (looks like a hose shoe, or an upside down U) or put it in continuity...this selection is pretty much the same as ohms for this kind of test, but has an audible indicator letting you know there is continuity Then place one probe (doesn't matter which one) where the plug goes on the determined circuit, (marking it with a marker is a good idea, they all look the same after a few min) and then poke the other lead into that circuit at the guage. If no continuity, then keep movinh the second lead back up the circuit untioll you have \ontinuity, once you obtain continuity, go back towards the guage in smaller incriments untill you don't have continuity anymore, and that will indicate an open circuit. If problems are found, repair/replace circuit board and test. If not...
replace the guage.
Do not worry about shorting anything out. Example, the green wire. When you unplig it, if it hits the frame, it will not spark. The guage reads amount of ground...or resistance to ground. 0 Ohms is tached out on the guage...way hot. 90 ohms (I think is the number on these) reads bottom cold.


If I left anything out, please feel free to add to this.
If it tachs out as you describe, then the circuit is grounded somewhere.

Guff, the sending unit should be the same regardless of engine if i am not mistaken. If the connector does not look like a nail head, then you have the wrong sender.

Thread tape can cause problems, and you really don't nead it anyways. The sending unit should be pipe thread. Pipe thread has a small tip, and gradually gets bigger as you thread it in. Hold one up infront of you in the light...you'll see it.
However, the thread tape would not cause the problem indicated, it would cause a guage to never move...stay bottomed out from lack of a good ground.

I had the same problem with my 71 with a 350. The temp needle hardley moved up at all when truck was warm and would peg full right if I grounded it so I thought the sender was bad. I made a trip to Oreilys and bought the correct sender for this year/engine (nail head type) and now when I start the truck cold the gauge goes almost all the way to hot within 5 minutes. It goes so far to the right that you would never really know if the engine were overheating.
I put the old one back in as it does move a little. Is there something about the gauges in these trucks? Several of us seem to have the same problem?
Surely others have figured somrething out. :confused:

[QUOTE=Longhorn Man]
Guff, the sending unit should be the same regardless of engine if i am not mistaken. If the connector does not look like a nail head, then you have the wrong sender.
QUOTE]

The parts book shows a different sending unit for big block trucks. I'm starting to think the previous owner stole my big block. :whine:

However, the resisitance should be the same. It was probably just a different size pipe thread.
I am speculating on that...but it sure makes sence. Otherwise, there would be another part number for the same guage.

Anyone have a picture of this "nail head" looking sender?

I decided to stop at Oriely auto on my way home tonight and the guy at the parts counter there said the 292, 350 and big block all used the same sender with the same part number. This was for a 71 c-10 with auto and air. Can anyone else verify this?
:crazy:

Any other ideas out there?