Joined: Aug 2017 Posts: 620 Threads: 7
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I have a 6v temperature gauge in fahrenheight which the needle moves the full distance left to right in its base slot as the engine heats up.
I'm hoping there is a resistor I can place in the sender wire to calm the results down to say half . At full scale the engine does not appear to be boiling. There is obviously a miss match here, how are senders rated?
At my recent front welch plug catastrophy I had no warning the gauge was already at full scale! thanks russell
Joined: May 2018 Posts: 2,952 Threads: 558
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Location: Peak District, Derbyshire
Car type: 1929 Chummy, 1930 Chummy, 1930 Ulster Replica, 1934 Ruby
As the Gauge relies on being in the water, would the gauge not drop to nearly zero if the latter disappears? I recall an incident driving a foul, rear-engined Fiat on the M1 when the temperature gauge reading started to drop. This was followed by a cabin full of steam as a hose, running from the engine to the heater, burst.
Joined: Aug 2017 Posts: 606 Threads: 19
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Location: Hampshire UK
Hi
Any more details of the gauge, or which car it was originally fitted to ?
Most (but not all) senders are a simple temperature dependent resistor. The resistance at normal running temperature depends on the sender, and there is quite a choice. You also need the correct thread form, assuming a screw-in type. With luck, you should be able to find a sender that gives a more sensible reading.
Although it's possible to tweak the reading by adding fixed resistors, this is only really useful for a minor adjustment. If you attempt too much, you may end up with a needle that doesn't move very much over a wide temperature range.
Joined: Aug 2017 Posts: 620 Threads: 7
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Hi John, the sender was a new one for a studebaker of the fifties and I will pull it out of the head to examine any part numbers, thread size and length . The gauge is a stuart warner and I recall it was stamped 6v.
The ruby is currently in a covered trailer which does not allow the bonnet to be opened. I shall sort this , read up about tests I can do and get back to you with more fact detail. Thanks for your interest.
Joined: Aug 2017 Posts: 620 Threads: 7
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I have the gauge out now and the number on the face is 429722, 6v is also there. Research indicates it may be part # D111W H1 . I have discovered the mounting 'U' bracket is supposed to be insulated from ground which it wasn't , my fault, probably explains a lot.
The sender 1/2" NPPT short is part 9004, no idea if it's appropriate. I will set up everything on the stove and report back.
regards Russell
Joined: Aug 2017 Posts: 606 Threads: 19
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Location: Hampshire UK
Hi Russel
From what I can work out from photos, the mounting bracket has insulators where the two "hot" terminals pass through it. With these in place, there is no problem connecting it to ground via a metal dashboard. The body of the gauge would be similarly grounded. There is a separate ground terminal on the gauge body, and unless you can rely on a good ground via the metal dashboard (chancy) it is best to fit a dedicated ground wire. Testing on the bench you will definitely need a ground wire.
I suspect the operating principle is the "two coil moving iron" type, which will be familiar to anyone used to A7 petrol gauges. Response to sender resistance changes is rapid, unlike the later era thermal types.
I have no information on the correct sender resistance range for 6 volts, but a typical range for 12 volt USA gauges would be 240 ohms cold to 33 ohms hot. The best approach might be to try a number of different value electronics style resistors in place of the sender, which will tell you what resistance corresponds to what temperature reading. Low power resistors are fine, with the demise of Maplin you could source them from CPC or internet auction. Alternatively, use a 1000 ohm variable resistor ('pot'), adjust it for each temperature reading and check its resistance each time (out of circuit) with an ohmmeter.
In a similar way, your sender resistance can be checked with an ohmmeter, with the sender tip immersed in 100 deg C boiling water, 12 deg C cold tap water or some blend in between.
Armed with this information we will be in a better position to decide if a different sender is needed, or if your original can be persuaded to work.
Joined: Aug 2017 Posts: 620 Threads: 7
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John your description of the connections is exactly correct. I needed to connect to the "hot" terminals AFTER the U bracket goes on, thus the insulators protect any stray current leakage. I had those nuts under the U bracket and the current diversion to ground caused full scale reading.
I have set everything with battery and stove etc, and the readings accord with my neighbours cooking thermometer.
Now we're cooking! thanks for the links which were very helpful
