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Water Temperature Sender


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#1 Mayfair'93

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Posted 26 June 2020 - 08:40 PM

Hello everyone,

The temperature gauge on my 1993 1275 A+ doesn't work. The needle doesn't move from cold. I believe the temperature sender is the cause which is fitted to the cylinder head below the thermostat housing.

I've bought a new sender (http://www.minispare...sic/GTR101.aspx) but it seems that the tapered seat end is longer than the existing sender which makes the new sender project further out the cylinder head than the existing.

I think the new sender is seating correctly in the cylinder head judging by the grime gathered on the tapered since from trial fitting.

I've attached a couple of photographs.

Any ideas on why the fitment is different or have I bought the wrong sender?

Thanks for your help!

E.

Attached Files



#2 nicklouse

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Posted 26 June 2020 - 08:45 PM

so does it work? if yes then there is no problem.



#3 MiniMadRacer

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Posted 26 June 2020 - 08:57 PM

As Nick says as as long as it worksit is not an issue.

 

I only ever screw in the senders far enough to stop leaks and no further, and I use PTF tape on the threads too



#4 Mayfair'93

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Posted 27 June 2020 - 08:20 AM

Thanks for the replies.

I haven't tested to see if it works as I didn't want to fill the system in case there was an obvious error.

If it works and doesn't leak I'll assume its OK.

Thanks for you help.

#5 Compdoc

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Posted 27 June 2020 - 02:22 PM

As Nick says as as long as it worksit is not an issue.

 

I only ever screw in the senders far enough to stop leaks and no further, and I use PTF tape on the threads too

Technically, you shouldn't use PTFE tape on a single terminal sender, as the sender body needs the earth connection to the block. This could give you false, or no readings, on the gauge

But as you say, if it works OK then the threads are obviously cutting through the tape and making contact.



#6 Moke Spider

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Posted 27 June 2020 - 06:31 PM

 

As Nick says as as long as it worksit is not an issue.

 

I only ever screw in the senders far enough to stop leaks and no further, and I use PTF tape on the threads too

Technically, you shouldn't use PTFE tape on a single terminal sender, as the sender body needs the earth connection to the block. This could give you false, or no readings, on the gauge

But as you say, if it works OK then the threads are obviously cutting through the tape and making contact.

 

 

I agree. These should be fitted without tape for these reasons and in any case, they don't seal on the threads but the tapered seat.



#7 MiniMadRacer

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Posted 27 June 2020 - 07:07 PM

I have always used ptfe tape for comfort and have never had an issue, but a fair point about the earthing..



#8 Chris1275gt

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Posted 27 June 2020 - 08:38 PM

Worked in a pipework installation industry for 37 years and never had a electrical continuity problem with any type of thread sealant on any steel, brass or copper threaded pipe the sealant only fills the very small anomalies at the bottom of the thread, they were always tested as the pipework was always earthed.

#9 Compdoc

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Posted 29 June 2020 - 08:56 AM

Worked in a pipework installation industry for 37 years and never had a electrical continuity problem with any type of thread sealant on any steel, brass or copper threaded pipe the sealant only fills the very small anomalies at the bottom of the thread, they were always tested as the pipework was always earthed.

As you say, in a pipework installation you need the extra sealing abilities of PTFE as the pipes often carry liquids at high pressure and screwing the pipe together allows the threads to cut through the insulated tape. Any connections that are not electrically sound will be picked up during testing.

The problem with sensors is they deal with tiny amounts of current by comparison, and rely on small changes in resistance to give an accurate signal to the gauge. Any extra resistance, even small, can give you an incorrect reading on the gauge. Personally, if I have the option, I choose a twin terminal sensor with its own earth terminal. That way a bit of PTFE if needed would not be a problem.



#10 Chris1275gt

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Posted 29 June 2020 - 06:47 PM

Worked in a pipework installation industry for 37 years and never had a electrical continuity problem with any type of thread sealant on any steel, brass or copper threaded pipe the sealant only fills the very small anomalies at the bottom of the thread, they were always tested as the pipework was always earthed.


As you say, in a pipework installation you need the extra sealing abilities of PTFE as the pipes often carry liquids at high pressure and screwing the pipe together allows the threads to cut through the insulated tape. Any connections that are not electrically sound will be picked up during testing.
The problem with sensors is they deal with tiny amounts of current by comparison, and rely on small changes in resistance to give an accurate signal to the gauge. Any extra resistance, even small, can give you an incorrect reading on the gauge. Personally, if I have the option, I choose a twin terminal sensor with its own earth terminal. That way a bit of PTFE if needed would not be a problem.

Hi compdoc
My point was that any amount of sealant on any thread would not affect the electrical continuity of the joint. The mini thermistor changes the voltage that operates the bimetallic driven temp needle so post themistor as long as you have a connection however small it will always operate normally.




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