Fauly aftermarket temperature sending unit?

[mcgarrett]

I'm having trouble with a replacement/aftermarket temp sending unit for my '40 Tudor I purchased a few months ago from 3rd Generation Auto. When first installed, it seemed to work properly...gauge needle moved to full HOT position on the gauge when ignition is turned to OFF and worked its way to the cold side of the gauge when ignition is turned ON; then it proceeded to indicate appropriate temperature. Now, the needle moves quickly to the furthest extreme of the COLD side of the gauge and doesn't move from there when ignition is ON and returns to the HOT side when turned OFF. Is the sending unit faulty? My gauge appears to be working correctly.

 

[TJ]

Put an extra ground wire to it and see what it does. Have you called 3rd Gen Auto and talked with Michael about it?

 

[petehoovie]

Michael will take care of you...

 

[Charlie ny]

X2 what PETE says.
Charlie ny

 

[mcgarrett]

I'll call them. I sent an email to them a while back but did not get a reply.

 

[tubman]

Aftermarket temp senders have a bad reputation. I have scrapped a lot of cast iron heads, but always save the temp sensors. They can even be repaired; see this post : https://www.fordbarn.com/forum/showthread.php?p=1509413&highlight=sensor#post1509413.

 

[mcgarrett]

tubman,
Thanks for your post. I have quite a few old sending units too. I'll try your repair process to see if I can get one working again as it should.

 

[mcgarrett]

The problem with my current sending unit (on the engine) is that the gauge's behavior is very erratic, for example; at times the needle seems to indicate temperature correctly by moving from the HOT side of the gauge when the ignition switch is in the OFF position and advancing slowly to the COLD side of the gauge when the ignition is switched ON and then proceeds to register temperature accordingly as the engine warms up. At other times, when the ignition is switched ON, the needle advances RAPIDLY to the COLD side of the gauge and remains there even after the engine warms up. I don't understand what is causing this. Any ideas?

 

[40cpe]

I would check for an intermittent short in the wire from the sender to the gauge. Might be the sender is bad but the gauge going quickly to cold sounds like a ground.

 

[mcgarrett]

40cpe,
I think you might be onto something there - I didn't notice any problems with the wire going to the sender, but I'll give everything another look.

 

[Pete pa]

Did you use Teflon tape when you installed your sender? If so, remove it you are isolating the temperature unit from grounding to the head.

 

[mcgarrett]

No Teflon tape or thread sealant used. Must be a problem with the wire going to the sender.