Temp Sender Hex?

jp928

Well-Known Member
Another one of life's mysteries. Why is the hex on the temp sender 18mm? This is a rarely used metric size, I only had one because I had a special need for a stubby 18 for some work on the 928. In the larger sizes 17 and 19mm are the standouts, 13 and 14 in the smaller sizes. 11/16 AF is a poor fit, so I got out the calipers and saw 17.90mm.
The old sender was REALLY tightly done up, and when I got it out the ally sealing washer was shagged. The supplied fibre washer was too thin - the cone on the sender hit the manifold well before the washer, so I had to scramble for a thicker fibre washer, none of my copper or alloy washers would fit.
 
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But what about my other little used metrics - they feel a bit left out. 32mm is lonely!
 
Those sizes list the hex as 18.03mm, so the fit would be marginal. As I said my calipers said 17.90mm, so my spanner was a nice fit. Not easy to get a shifter in there. Hex was same on new item (568055) as the original. I am hunting for what I think is an undereading gauge....or maybe a missing thermostat.
 
The new temp sender seems better. Driving along easily (ambient ~20C) indicated low end of the green; idling in traffic for a bit it eased up nearer the middle, so happy with that.Extended idling before would barely get near the green.
The thread - 18tpi, but OD is 0.605".. neither 9/16 (.562) or 5/8 (.625). very strange. Next job is get the leaking overflow pipe in the filler neck fixed, and the rad cleaned.
 
I suggest that the thread is 5/8" UNF. At .625" and 18 tpi it is the likeliest candidate. 3/8" NPT is also 18 tpi, but has a major diameter of 0.675"
3/8" BSP has a major diameter of 0.656" and is 19 tpi.
 
3/8 NPT of course tapers, so the major diameter the thread is going to depend on where you measure it. The taper is .75" per foot, so if the thread is an inch long it would be .6125" or so at the tip, which is getting close to the mystery thread measurement.

Yours
Vern
 
I don't think those large senders have a taper thread as they usually have a thick sealing washer.
I have seen the smaller senders with I think a 1/8" NPT thread.
 
Definitely NOT tapered. NPT senders are common on US made stuff, BSPT on a few.
One of the strangest threads I have seen is on Porsche towing hooks - they screw into the front or rear bumpers (alloy things) through a hole in the plastic (PU) bumper covers. They have a sinusoidal thread profile, and are in two sizes known as 15 or 20mm. They are actually 0.6" or 9/16" OD, and 8tpi ! The proper name for the thread is KNUCKLE - look it up. Apparently this is designed to tolerate bad conditions where debris is likely, as in firefighting hoses and equipment. Sadly they are not at all robust, being either cast from something fragile, or sintered. You can only pull on them in line with their length - anything lateral will snap them.
 
Hi, In common with a lot of other makes, I think it's to stop over use or abuse. They have only got one job to do and are made to cater for that. I think the term is 'waiting to work' a bit like a ring pull on a beer can.

Colin
 
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