I can't find an answer to this on the wiki or in the forum old threads: does the temperature sender use a gasket? I ask because over the years I've gotten two different aftermarket temperature senders that go to the (weird, multiple gauges in one dash space) meter, and both of them fit fine and the nut/bolt thing screws in just fine, but the temperature sensor is just rattling around loose in there and needs a 3mm thick spacer between it and the nut that screws into the head, and that indicates to me that this may be a standard size but needs a gasket.

The Datsun 1200 temperature sender uses a taper seat for sealing

Nissan 25080-89900 GAUGE-TEMP ENGINE UNIT

Attach file:

---

  sealing.jpg (25.11 KB)


  25080-89900.jpg (42.19 KB)

Quote:
It might something on the threads that is not allowing the nut to screw all the way in. Perhaps some corrosion or some old "pipe thread tape" somebody used in the last 50 years, not realizing these are regular threads. Try running a blind tap down the hole to clean up the threads

oh and to answer your question, no there is no gasket used on the temperature sender

I really appreciate the input and am very confused by what I have in this case and why it isn't sealing well. I'll work on it. Thanks!

Still isn't working: I've tried three different temperature senders and I'm cranking them down so hard I'm starting to round off the nut that tightens them down. Water comes shooting out of it like there is almost no flow restriction at all. You can see an indentation in the sender where it's been pressed against the cast iron engine block, so it's definitely in there solid. I wish I'd never taken it apart!

I ran a tap down in there and same thing. I think the seat on the block is damaged somehow, based on putting some blueing on the sensor taper and tightening it down.

Yes, sounds like the head has minor damage, as the sender does not require very much torque

Perhaps some JB-Weld will fix it, or maybe just replace the head. Time to go big-port?

I would try JB Weld as well. I'd let it partially set before assembling it.