highcking Posted July 19, 2013 Share Posted July 19, 2013 I need to replace the temperature sensor on my '58. A previous owner installed an aftermarket electric unit that I've removed. The original unit is still in place - the sensor is hanging loose near the distributor. The threading on the aftermarket sensor exactly matches the threading on the original sensor. It is clearly pipe thread, but I am puzzled by the fact that both fittings have four flat sides on the threads at 90 degrees from each other. It looks like the threads were ground down by a factory process. The fitting does not leak. Nor does a standard 3/8" NPT fitting screw into the block hole.What am I missing? I can't recall seeing a fitting like this, and I wonder why it doesn't leak.Bill Shields Link to comment Share on other sites More sharing options...
Smartin Posted July 19, 2013 Share Posted July 19, 2013 The sensor itself has a lip on it that keeps it from going too far into the hole in the head...the nut then will "bottom out" on top of the lip and pinch it, sealing the hole. Link to comment Share on other sites More sharing options...
Bhigdog Posted July 19, 2013 Share Posted July 19, 2013 SMartin is exactly correct. The bulb fits in a counter bored threaded hole. The nut compresses the lip of the bulb between it and the hole bottom. I like to put a thin coating of aviation permatex on the underside of the bulb lip. Probably not needed but can't hurt. BTW, it's not pipe thread..............Bob Link to comment Share on other sites More sharing options...
highcking Posted July 19, 2013 Author Share Posted July 19, 2013 Thanks for the replies - that tells me what I need to know!Bill Shields Link to comment Share on other sites More sharing options...
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