How do I seal an original temperature sending unit

[coxswain98]

I have the liquid bulb type sending unit. The bulb goes into the head, the nut then threads into the head. How is it sealed between the free floating nut and the tube? Am I missing a rubber flange or something?

 

[Kube]

Most likely you have an incorrect head.
Look down the threaded hole for the sending unit. You should see a machined "flat" that the unit would be pressed against when installed. If what you is a straight hole with threads, well, wrong head.

It would help to know what year you are working on and even more importantly, what year is the engine?

 

[19Fordy]

I have used JB Weld on 8BA units.

 

[motordr]

You require a special adapter fitting, NPT thread that goes into the cylinder head and a seat that the bulb seals on. No gaskets.

 

[restoman]

I have some of the adapter fittings and if that is what you need email me and I'll send you one. If your head is the correct one, 78xxxx or 81xxxx the brass on brass will seal well with just a little grease to help seat it.

 

[deuce lover]

You need an adapter. Here are pics. Male end(NPT) goes in the head (37-48)and then the bulb with nut in the female 5/8 X18.You see in that adapter where the bulb seats when nut is tightened. John Wolf in OH or Williamson's should have the adapter .You were offered one by a member here also.

 

[TerryOH]

If your head already has the seat for the sending unit or once you install the fitting above, there is no other seal needed, the small lip on the bulb is compressed on the seat by the nut on the bulb. Make sure the seat is clean before install and the threads for the nut are also clean.

 

[deuce lover]

...

 

[Tim Ayers]

I got mine from Moroso (the aftermarket performance company). Common part used for a lot of different temp senders.

Looks like some nice folks offered to send you one as well.

 

[restoman]

The adapter is used only on 40 to 48 heads, not on 37-39.

 

[Kube]

The adapter is used only on 40 to 48 heads, not on 37-39.

I tried to explain that in post #2.
However, the original poster never answered my questions, so all the responses thus far are nothing but conjecture.

 

[danliveshere]

I had trouble fitting my 35 temp bulb into a Motor City Flatheads head, because the bulb is too long and hits the casting inside the head. So the solution was to machine an adapter that screwed into the head and stick out far enough to fit the bulb. Doesn’t answer your question exactly but you have to think outside the box sometimes to overcome problems especially when modifying components. By the way the early bulbs are supposed to screw into the water pump not the head. Hopefully you have found a solution already.