Electrical oil pressure sender won't screw in

[Reg]

As the last sender had lasted 14 years I opted to replace it with another one rather than go mechanical. When I attempted to fit the new one the thread would not engage. It's a model year 2000, 1800 K-series Roadsport so has an M12x1.5 thread. That's the same as the wheel nuts so I tried screwing a wheel nut onto both the old and new sensors - that worked fine, so the thread on the new one is good. But every time I attempt to fit the new sensor it feels as though it's cross threading and stiffens up with half a turn of the thread feeling as though it's engaged. What on earth is wrong? (apart from the fact I should be replacing it with a mechanical gauge 😬)

[Stationary M25 Traveller]

Look at the thread on the sender .... any burrs or damage ?

[Jonathan Kay]

What does the sensor look like? Current Caterham list.

 

Does the old one tighten up OK?

 

Inspect and clean both threads, as above.

 

Jonathan

[Bob L]

May just be a bit of grit / sealant on the female thread. Screw in a piece of paper towel gently. This may remove it. If it feels like it snags, it could be the thread. Feel with the tip of your little finger but watch for cuts!

[Reg]

Thanks chaps.

 

Ian - no, believe me I've examined the threads in microscopic detail and am now a leading expert in metric thread sizes. It looks absolutely fine and, as I say, a wheel nut screws onto both it and the old sensor with no resistance whatsoever

 

Jonathan - it's the post-98 one for a K-series. The new one and the old one both have identical identification marks on them (which include reference to the M12 thread size). The old one fits back on absolutely fine, I've put it on alternating with the new one so many times now, trying to see what's different.

 

Bob - I don't think there's any foreign matter in there. I gave it a good clean before removing the old one and have since given the female thread a good seeing to with some paper towel. Also, if there were, the old one wouldn't screw back in, which it does.

 

The sensor fits extremely closely to the casting it screws into. There's almost no clearance at all and I wonder if there's some tiny difference in the size or shape of the new one that's not allowing the thread to engage correctly.

[Jonathan Kay]

I don't think you have many options left. You could measure with callipers to see if it is oval, but whether it is or not I'd recommend asking for a replacement.

 

Jonathan

[Reg]

Serves me right I suppose - I chose the electrical sensor option because it would be less hassle I might have known what would happen 😬

[Jonathan Kay]

Thanks for sharing!

 

:-)

 

Jonathan

[AdamQ]

This is a vague and distant memory dredged up from the darkest and dimmest recesses of what I call my mind, but I seem to recall a similar problem and it was down to the new sender being very slightly larger in diameter than the old one and the sender body was fouling on something - can't remember or think what it might have been - as I tried to screw it in.

 

Thought it worth mentioning as you seem to have all but eliminated thread differences and 'when one has eliminated the impossible, whatever remains, however improbable, must be the truth' ...

[Piers Rendell]

I think these sensors are now made in China and build quality may be an issue.

 

My company sell Oil and Water temp sensors for industial diesel engines and we tried some Chinese made units and tested them in our engine test bed. Most failed within 2 hours, so we gave up and stayed with VDO.

 

Piers

[Reg]

Well, Darren has sent me a replacement unit and it seems to me that the threads must be very poorly cut - the thread on this one binds too just like the first but not quite so severely so with this one I can screw it all the way in by hand. Perhaps the first one would have been OK if I'd applied sufficient force but I wasn't about to find out.

I was figuring that Adam's explanation was the most likely but it appears that Piers had the right answer - they're just plain badly made.

Top marks to Darren and Caterham spares for swapping the units so quickly and with no grumbling.