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Fuel & Temp Gauge Troubleshooting

hartmandm

hartmandm

Moderator
Diamond Level Sponsor
The topic of troubleshooting issues with series III, IV, and V fuel and temperature gauges comes up on some frequency on our forum. Folks spend time re-typing much of the same info each time. I've compiled info for the gauge circuits and troubleshooting into a single document.

Here's the document: http://mhartman.net/files/sunbeam/fuel & temp gauges.pdf
The document has also added to my document index at: http://wp.mhartman.net/home/cars/sunbeam/alpine/info

Feedback / suggested updates welcome.

Thanks,
Mike
 
DanR

DanR

Diamond Level Sponsor
You do good Mike! Lots of great info in the documents you prepared. I know for sure many will benefit from your time and effort to spread the word on "How to"....
 
T

Tom H

Platinum Level Sponsor
Very nice work, Mike. This will be a great resource for the many who encounter gauge problems on SIII - SV Alpines. I offer two possible additions/ changes, you may find useful:

1) under Gauge (bottom of Pg 3), to test, I would suggest it might be easier to test the gauge by removing the lead at the sender and grounding that wire, rather than removing the wire at the gauge and connecting a ground wire to the gauge terminal. Seems easier than bending under the dash.

2) A handy way to test the "calibration" of the gauges is to connect the gauges in series , with one end connected to power and the other end grounded. This provides each gauge with a simulated sender resistance of about 61 ohms, which should read slightly above mid scale on both gauges.

Tom
 
Ken Ellis

Ken Ellis

Donation Time
It's a good read, and covers quite a bit in-depth.
Do you guys think it should briefly cover failure modes? As in, 'if the original design voltage stabilizer is not working correctly, you may notice an indication of the engine running hot without other symptoms, or having slightly more gas than you actually have.' Or words to that effect...

Possible addition when checking with analog meter or light would be:
When reading voltage stabilizer output, if the analog voltmeter reads either 0V, or stays at 12.5V/14.4V, (or the test light either doesn't light, or stays on all the time), then the voltage stabilizer is bad.

In any case, I think explicitly telling folks "what it looks like when it's broken" may be beneficial. Few will be doing these measurements if everything is working correctly.


And, checking either sender by substitution could be along the lines of:

Substitute a 77 Ohm resistance for sensor and verify mid-scale reading. Wiring a 140 and 170 Ohm resistor in parallel will give 76.77 Ohms, which is close enough for test purposes. Or, take a 1k Ohm potentiometer and adjust it for 77 Ohms from the center terminal to either end terminal. If the gauge reading is high, then the voltage stabilizer has probably failed. If the gauge reading is low, or absent, suspect either wiring, grounds, or voltage stabilizer.

If I have overlooked this stuff in the write-up, I can only blame the lateness of the hour. If you guys think it's beyond the original scope, that's fine too. And a chart may be better than a wall of text.

Thoughts?
 
hartmandm

hartmandm

Moderator
Diamond Level Sponsor
How do original stabilizers typically fail? I would guess they fail in two ways - "open" or "closed".
1. Open: The "I" connector has no voltage.
2. Closed: The "I" connector continuously provides a voltage. Normally the internal resistance of the stabilizer reduces the voltage at "I" from the battery voltage (car off ~12.6V) or alternator regulated voltage (car running ~14.4V). Would you expect to see the reduced voltage at "I" or a short between "B" and "I" and see full voltage from "B" at "I"?

I can add the details for replacing the sender with a potentiometer. I figured the combination of the ground test plus gauge calibration test should show if the gauge is working somewhat ok. But the potentiometer test can help assess the level of (in)accuracy. No reason not to include the details.

Thanks,
Mike
 
hartmandm

hartmandm

Moderator
Diamond Level Sponsor
FYI - Per Ken's suggestion, I'm working on adding a table of 'Symptoms' and 'Possible Causes' to the doc. Hope to have that done shortly.

Also realized I had left out details on how to orient an original voltage stabilizer and how it is grounded.

Mike
 
DanR

DanR

Diamond Level Sponsor
Quote: Also realized I had left out details on how to orient an original voltage stabilizer and how it is grounded. Mike. Unquote

THAT WOULD BE A REAL NICE ADDITION. I was looking for that info this afternoon while hooking back up some wires,
 
T

Tom H

Platinum Level Sponsor
Ken,
You made some good suggestions. But I think suggesting substituting resistors for the senders for test purposes is less useful. I think anyone who knows where to buy or has access to resistors or potentiometers is probably already knowledgeable enough to figure out how to test. Mile's document has already shown how to do a basic test of the system by simply shorting the sender lead at the sender. A more detailed test by wiring the gauges in series uses the 61 ohms of the gauges as a "test sender" and uses stuff already on hand. Might makes sense to add that if you have a spare gauge of either type you can use that spare gauge as a "test sender", again should read slightly above mid scale. Maybe we can do a little testing to see more precisely where a 61 ohm "sender" should cause the gauge to read.

Tom
 
hartmandm

hartmandm

Moderator
Diamond Level Sponsor
Tom,

I have a test bed setup to work through gauge behaviors under various setups. The test bed is a couple of series 4 gauges, a variable linear DC power supply, a couple of original voltage stabilizers, potentiometers, etc. Hoping to finish documenting the behaviors soon.

I am also looking at documenting gauge reading differences between the original voltage stabilizer and a 10.0V solid state stabilizer. Also prototyping a 10.8V solid state stabilizer.

Mike
 
hartmandm

hartmandm

Moderator
Diamond Level Sponsor
DanR said:
Quote: Also realized I had left out details on how to orient an original voltage stabilizer and how it is grounded. Mike. Unquote

THAT WOULD BE A REAL NICE ADDITION. I was looking for that info this afternoon while hooking back up some wires,
Click to expand...

Dan,

Did you find the info you needed?

Mike
 
Ken Ellis

Ken Ellis

Donation Time
Tom H said:
Ken,
You made some good suggestions. But I think suggesting substituting resistors for the senders for test purposes is less useful. I think anyone who knows where to buy or has access to resistors or potentiometers is probably already knowledgeable enough to figure out how to test. Mile's document has already shown how to do a basic test of the system by simply shorting the sender lead at the sender. A more detailed test by wiring the gauges in series uses the 61 ohms of the gauges as a "test sender" and uses stuff already on hand. Might makes sense to add that if you have a spare gauge of either type you can use that spare gauge as a "test sender", again should read slightly above mid scale. Maybe we can do a little testing to see more precisely where a 61 ohm "sender" should cause the gauge to read.

Tom
Click to expand...

Yeah, I'll buy that. When I was writing that post, I remember pondering where a non-electronics person would come up with 77 ohms of resistance conveniently and cheaply. Now that Radio Shack is history, you really can't pop in and grab a resistor or two for $1.19. It's more of a production, and less likely to happen. Even looked thru various resistors available at auto parts stores, but didn't find anything cheap enough at the right target values.

And to Dan R. ... mine was labeled. I'm holding the mounting tab.
Sorry for the crappy out-of-focus shot from years ago... (but at least the tape machines are in focus.)

IMG_0752.JPG
 
T

Tom H

Platinum Level Sponsor
Mike, I just e-mailed you a report I wrote after testing 4 of these gauges and 1 stabilizer several years ago.
 
mightyohm

mightyohm

Donation Time
Great article. Would love to see series II included as well. As far as I know the temp and gas tank senders for the early cars are NLA.
 
T

Tom H

Platinum Level Sponsor
Jeff, I'd love to test and report on SI /SII gauges if someone would loan me a pair that I could test.

Tom
 
65beam

65beam

Donation Time
Victoria British did have some new early gas tank sending units. I bought one for the red Harrington. If your early unit is a Smith's unit Nisonger can rebuild it. They rebuilt the one for the white Harrington. They put a one year warranty on it.
 
DanR

DanR

Diamond Level Sponsor
Tom, I just might have a set of the fuel and temp gauges for a Series I/II, and would be glad to send them to you.
 
mightyohm

mightyohm

Donation Time
65beam said:
Victoria British did have some new early gas tank sending units. I bought one for the red Harrington. If your early unit is a Smith's unit Nisonger can rebuild it. They rebuilt the one for the white Harrington. They put a one year warranty on it.
Click to expand...

Nisonger rebuilt my series 2 fuel sender unit. It seems to work fine, although the car isn't on the road so running out of gas is not a problem I have had to deal with, yet!
 
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