Bad sending unit?

[48builder]

So I think I have my cooling problem solved. I bought a Cooling Components shroud and fan along with their 2-speed relay. I took my Walker radiator to a local shop and had it flushed and they repaired a couple leaks. Put it all back in and the shroud looks and works great.

However, I now think my temp gauge sending unit is bad. The engine warms up fine, but when it gets to about 200 the needle starts fluctuating wildly and then just pegs all the way over to the max. The fan runs and cycles off like it's cooling fine, but the gauge stays pegged.

I checked the lead to the sending unit and it was clean and tight. Sound like a bad sending unit?

Walt

[416Ford]

Just checking but you are running the fan and the gauge off two different senders correct?
Does the gauge go off if you disconnect the sender?
If so I would agree with you and try a new sender.

[wayne petty]

run the 4 part voltage drop test
make sure that your ground connections are properly attached. as temp senders are usually 1 wire.. the other side of the circuit is thru the engine block to firewall ground.. firewall on the inside to the gauge cluster..








at higher rpms the alternator output can exceed the weak ground connections and the regulator starts cycling voltage..  causing your gauges to flicker..

current from the alternator is sent out thru the housing.. into the block

the negative current on the block is higher than what is coming out of the battery .. so the electrons  come from the engine via a ground strap..

[unklian]

pull it out, and check it in a pot of boiling water.

[48builder]

Just checking but you are running the fan and the gauge off two different senders correct?
Does the gauge go off if you disconnect the sender?
If so I would agree with you and try a new sender.

Yes, two different. I'll disconnect tonight and see what happens. Thanks

[48builder]

Thanks, Wayne. I'll do this test.

[48builder]

As it turns out, I had a comedy of errors in my temp gauge. I first discovered that my ground wire from the block to the body was loose where it mounted to the body. I took it off and cleaned it and then tightened it down.

Then when I took out my old sending unit I discovered that I had used Teflon thread goop on it. That's a no-no but must be when I built this car 25 years ago I didn't know that.

Then I discovered a loose wire on the gauge itself.

So now that I have all of these things fixed my gauge works well, and so does my new cooling fan. Perhaps I didn't need the new fan after all but I'm glad I put it in. I feel better about the whole system now.

Thanks for all the help.

Walt