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Discussion Starter #1
Something is wrong with the water temp gauge in my 750 spider, and I can't figure it out. Any help will be appreciated.

It shows no temperature reading even after it is obvious the car ir warm enough. Initially I thought the sender had gone bust, so I put in a new sender and nothing changed.

If I disconnect the cable from the sender and ground it, the needle goes to the top as expected.

I have reversed the oil and water cables at the back of the instrument, and when the oil temp gauge is connected to the water temp cable, it shows an adequate reading....

So the sender is OK, the wiring is OK but the instrument is obviously not OK.

Thanks
 

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But Mad North-Northwest
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You likely need to adjust it. Assuming it is the Jaeger tri-gauge there are two adjusting screws on the back for each needle: one for the "hot" coil and one for the "cold" coil. You need to loosen the screws and adjust the positions until the gauge reads (sort of) correct.

See docs below. Instead of using a pot of boiling water, you can also temporarily replace the sender with an appropriate resistor. For the sender in my 101 Giulia with Jaeger gauges the resistance curve was:

Ohms = 6015.5 * e^(-0.01763 * Temp in F)
 

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Now, this is interesting stuff! Having owned Alfas for over 50 years, and a G'etta for almost 50 years, I have never heard of this....one is always learning. Thanks Gubi!

Richard
 

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Thank you Gubi, I have exactly the same issues as hdavis (first poster) with our `62 Spider and after checking the gauge by grounding the sender wire I`d come to the conclusion the sender was faulty and have another , plus oil temp sender ordered via Classic Alfa. I never knew that these gauges were adjustable and if it weren`t for you sharing this info I no doubt would have condemmed the gauges after replacing the senders and ending up with the same result - not reading. Extremely helpful - thank you again.
 

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Discussion Starter #6
Thank you Gubi, I have exactly the same issues as hdavis (first poster) with our `62 Spider and after checking the gauge by grounding the sender wire I`d come to the conclusion the sender was faulty and have another , plus oil temp sender ordered via Classic Alfa. I never knew that these gauges were adjustable and if it weren`t for you sharing this info I no doubt would have condemmed the gauges after replacing the senders and ending up with the same result - not reading. Extremely helpful - thank you again.
I was just about to do the same, I was already scanning eBay for a decent used gauge, so I'm very glad Gubi shared this info.

Besides it will be a fun project for this isolation period...
 

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But Mad North-Northwest
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Happy to help. I'll also note that on my car the gauges were somewhat voltage sensitive, in that they read lower with the car off than the car running. When I calibrated them in the car a second time I did it with a battery charger attached to provide voltage closer to a running car. I won't say they're super accurate but they're reasonably close now.
 

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You likely need to adjust it. Assuming it is the Jaeger tri-gauge there are two adjusting screws on the back for each needle: one for the "hot" coil and one for the "cold" coil. You need to loosen the screws and adjust the positions until the gauge reads (sort of) correct.

See docs below. Instead of using a pot of boiling water, you can also temporarily replace the sender with an appropriate resistor. For the sender in my 101 Giulia with Jaeger gauges the resistance curve was:

Ohms = 6015.5 * e^(-0.01763 * Temp in F)
What year Alfa Owner magazine did this article come from? Curious if I can find the digital version on the AROC website.
 

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That`s another good tip about being voltage sensitive. I had realised that but wondered about the easiest way of allowing for it when the gauge was out of the car and being adjusted. I`d resigned to having to take it in and out until it was obviously satisfactorily accurate.
One thing with an old car is that there is always something to be fiddled with to get better than before which is great for maintaining sanity during isolation. Hooray for hobbies.
 

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Discussion Starter #11
You likely need to adjust it. Assuming it is the Jaeger tri-gauge there are two adjusting screws on the back for each needle: one for the "hot" coil and one for the "cold" coil. You need to loosen the screws and adjust the positions until the gauge reads (sort of) correct.

See docs below. Instead of using a pot of boiling water, you can also temporarily replace the sender with an appropriate resistor. For the sender in my 101 Giulia with Jaeger gauges the resistance curve was:

Ohms = 6015.5 * e^(-0.01763 * Temp in F)
So, following the instructions on the document you attached I started by checking the electromagnets by measuring the continuity as described. But I am probably doing something wrong.

No matter what gauge I check and what test I do I end up getting a very similar reading of 70 - 75 ohms. I did 4 tests, 2 on the oil temp gauge and 2 on the water temp gauge. On each I first connected the voltmeter first to the + terminal and to the gauge case and then to the + terminal and the COM terminal. As you can see in the pictures below, in all 4 of them I end up with a similar result.

According to the article I should get around 250 ohms for the first test and 95 ohms for the 2nd test. Now 70 - 75 could be kind of close to 95, but very far off 250. The strange thing is that the oil temp gauge clearly works (though it probably reads on the high side).

I will nevertheless go ahead and try to calibrate it. The article says that the hot force magnet is normally the one needing calibration and that is the one that is reading somewhat close to 95.

Will report results later

Henry

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But Mad North-Northwest
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You need to measure from + to case with the black power wires you've got there disconnected, I think. Otherwise you're measuring all three gauges in parallel, which ain't what you want.
 

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Discussion Starter #14
Anyway I continued with the procedure as described in the document and it seems to have worked reasonably well.

This is the reading I got after a couple of minutes after the water came to a boil, basically the time it took to walk with the pot of water from the kitchen to the garage and connecting the power source, putting the sender in the water, and moving the magnet a bit.

Not perfect but good enough I believe. The needle is very sensitive the movement of the magnets and it would take a lot of trial and error before getting it perfect (and a number of boiling water pots, since I don't have a proper resistor).

I have not installed the gauge back in the car, will do so tomorrow and go for a drive.

Thanks again

Henry
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