Temp gauge

[edison1970]

Maybe someone can think of a reason why my temp gauge is not working. I replaced all of my gauges a few months ago with another set I bench tested before I installed them. All are working except the temp gauge. Put power to it and it sweeps. Tested the wire from the sending unit to the fire wall, good; tested from fire wall to back of gauge;  good; tested the sending unit with ohm meter with adding heat; working, tested with ohm meter to block and it is making ground. What am I missing? Can the gauge still be bad even though it sweeps when I put power to it? Appreciate any thoughts on this.

[Bullitt-]

Try grounding the wire that attaches to the sending unit.. should peg the meter, if not there's a poor connection given that the gauge is good.

[edison1970]

Ran a jumper to the negative side of the battery and turned on the ignition.  The gauge pegged.  Not very smoothly but it did. So does that tell me the sender is bad

[Bullitt-]

could be or sender not grounded well..  Do you have a negative battery cable attached to the block?

the "not smoothly" makes me wonder if there's not a poor connection somewhere

[RUNCHARGER]

I don't like to shotgun parts at a car but it sounds like a new sending unit is a good idea.

[anlauto]

I had an issue like this with a customer's car...ended being a faulty brand new sending unit...of course I didn't figure it out, because the sender was new so I figured it was good

[edison1970]

I checked the grounding of the sender. I touched the ohm meter to the end of the sender and the other to the block and it was good.  When I tested the gauge on the bench, it didn't move that smoothly then. I have another gauge from my old cluster. I think I'll jump the wires from the old gauge to this one and see what happens.  I'll also try running a new wire direct from the sender to the gauge and eliminate the chance of a bad wire. If all else fails, I'll try a new sending unit. I'll let you know the results.

[dodj]

So does that tell me the sender is bad

No.

I checked the grounding of the sender. I touched the ohm meter to the end of the sender and the other to the block and it was good. 

What are you calling good?
Good would be 80 ohms if the engine is cold. Heat it up and it should go to 10 ohms.
IMO, do what bullitt suggested in his reply. Ground the wire from the end of the sending unit. Turn on the dash and you should get full sweep.If you don't, the gauge or the wiring is the problem. If you do get full sweep, the sender is the problem. Hopefully the sender was not installed with silicone or teflon tape. If it was, remove it and clean it, and reinstall. It needs a good electrical connection to the block.

Good Luck!

[Rich G.]

If you ground the wire and the gauge went up everything from the wire to the gauge is good. Are you using any sealer on the sender? That could prevent the sender from getting a ground.

[edison1970]

No sealer on the sender. I'm going to attack this again tomorrow night.  My brain is fried.

[Chryco Psycho]

You need a new sender , the one you have may be the wrong range

[dodj]

No sealer on the sender. I'm going to attack this again tomorrow night.  My brain is fried.

Assuming your engine ground wire is installed,
You need a new sender.
When you get it,you can "kitchen". Test it with a pot of boiling water. Check the resistance cold. Should be 80 ohms. Put it in a pot of boiling water. Should read 10 ohms - connection. post to threads.
Don't be too concerned if it's ends up 78 & 12 ohms or similar. But if it's like 100 & 30 ohms it's the wrong range.

[73chalngr]

I had a similar problem when I went from aftermarket gauges to rallye gauges the aftermarket sender was different than the rallye sender .

[JS29]

I suspect the sending unit, The unit is the same for rallye or standard. It's the oil sending unit that differ from the standard to rallye cluster. 

[73chalngr]

Yes the oil sender is different. Standard gauges have an idiot light , rallye gauges have a gauge .