No matter what I do, this thing always seeps... Anyone have this trouble?
351w, dolphin gauges and sending unit. You can see it in this pic if you zoom in

 

I can't tell (because I am to stupid to make it zoom on the computer) but if it is leaking around the threads try pipe dope instead of teflon tape. At least it looks like teflon tape in the photo to me.

 

I have been using Teflon tape. I'll try the pipe sealant liquid stuff.

 

Locktite makes a thread sealant that we used to call liquid death cause it was so hard to undo , but it sealed very well

 

This look like it?
http://www.all-spec.com/products/56765.html?gclid=CL7E1crzpcwCFZFcfgode3QBLg

 

Permatex advises (at least their rep' that came and held a class at our shop) that both tape and dope should be used together for best seal. The trucks I work on have many air and fluid lines and I don't have time to piddle with not using both. I never have any leaks doing it this way.

 

Teflon tape is no a sealant , it is a lubricant that allows the friction fit seal of NPT junctions to thread together enough to seal . If the NPT fitting is cut too small you will need some kind of goop (preferably hardening) to seal it up .

 

The depth of that threaded hole is SHALLOW...if you are having trouble getting a good seal I would look into the possibility that the sending unit is actually bottoming out. The only reason I know about this is because I recently had to rework that hex rod on my 351W to add a sender for my aftermarket oil pressure gauge...the big sender on the end of the rod is an electric fuel pump cutoff switch.