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Temperature sender?


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I started the engine (Kubota/Nanni N438HD) recently and the water temp alarm came on while the engine was still cold. I soon found a frayed wire to the temperature switch and replaced it thinking the problem solved. 

We then ran for 2 days, 18 miles without issue until yesterday when it went off again. The engine had done about a mile.

I thought of changing the sender/switch and was quoted between 83 and 130 pounds!

I'm wondering whether the problem might be at the other end in the circuitry.

Any ideas/similar experience?

I have attached a photo of the switch and control. 

 

20210611_093938.jpg.335c0c1db6f6d3c426d51483eb56ff8e.jpg

20210611_094630.jpg

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If you have a multimeter you should be able to check the sender, I'm not familiar with those engines but there could be two types of sender - a fixed temperature switch or a thermally variable resistance. As you only have a warning light only a switch is needed, but they may have found that the cost difference between the two items meant it was easier to fit a thermally variable in all engines and include circuitry on the basic panel to set the warning light temperature, the deluxe panel having a gauge instead.

 

Measure the resistance across the sender cold - zero or nearly - sender shorted - replace,

                                                                           - infinite - open circuit, may be a switch - needs warming to test further, OR failed variable.

Heat the sender, if you can keep the meter connected it will be useful. Boiling water should be sufficient as a heat source.

If the resistance gradually changes (either up or down) then it is a variable sender and is probably ok, if the resistance suddenly changes from infinite to zero then it is an ok switch, either way the problem is elsewhere, 

Does the light come on when the sender is disconnected ?

 

springy

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Sounds like the rest is ok and its the sender that's closed when cold, if you don't have a meter you can reconnect the wire to the sender and hold the body against the engine block - if it lights up then faulty sender.

 

springy

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Just had to replace the guage and sender on my engine and did not come to the price you quoted. You need to know what thread the sender is and what temp do you want the alarm to sound at. I got my sender from Asap supplies.

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5 minutes ago, Jim Wortelhock said:

We have just cruised for 2 hours with no issue. Shows how intermittent problems are so puzzling. 

 

But how do you know if it is going to work if the temperature reaches 98 degrees

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6 minutes ago, Jim Wortelhock said:

I did. They want 83 quid plus postage! Another quoted 133. I have found some on eBay but the postage and charges make them no cheaper. 

But did you ask them what thread size was it

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Its a Japanese base engine, so my guess would be metric is likely. Try a Kubota agricultural dealer/agent. I would take the old one to match the thread as best as possible by eye. You could tell that the pitch was OK fairly easily.

 

Google "Kubota tractor parts UK"

Edited by Tony Brooks
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30 minutes ago, Jim Wortelhock said:

True.  I'm going to source a replacement first chance I get.

Trouble is determining the thread. 10mm and 3/8 are very similar in size.

Another possibility is 1/8 BSPT (British Standard Pipe - Taper). A taper thread is good as it needs an electrical connection between the sender and the engine block to work. It is hard to tell from the photo, but it looks to be tapered. A taper connection doesn't need ptfe tape, or other sealant that can interfere with this. 1/8"BSPT is 9.728mm major diameter. Can you measure the number of threads per inch? 1/8BSP is 28 threads per inch.

As @Tony Brooks said, compare the old with the new by eye meshed together.

Jen

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Just now, Jim Wortelhock said:

Thank you Jen. All good advice. 

I didn't know about counting the threads per.

Once I get near a good Chandler I can remove it again and compare.

 

Curious why you are happy to pay the marine mark up when a little bit of Googling may well get you an industrial one cheaper.

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40 minutes ago, Tony Brooks said:

 

Curious why you are happy to pay the marine mark up when a little bit of Googling may well get you an industrial one cheaper.

 

Especially when in his 1st post he has said he is not overly impressed to pay the 'marine' price between £83 and £130.

 

I think I paid about £5 for my Ford engine one when it went do-lally (Ford Cargo truck engine)

 

When I've had boats with Yanmar or Kubota engines I've always got spares from the local excavator / plant parts suppliers at a small fraction of the 'marine ' price.

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