Fuel & Temp Gauge Troubleshooting

[Boobtube]

Beam, He has SIV. I know that from previous posts by him, but also can tell he has later series gauges by the fact that he is trying to follow instructions on later series and the fact that he measures each gauge about 65 ohms.

Ken, a 9 V battery will be about 8 volts when loaded with 100 mA or so. Each gauge takes about 130 mA at full scale, about 75 mA at mid scale . Better to just use the direct vehicle battery voltage for reasonable test, as suggested by Mike.

Boob, you are seeing some strange behavior. I am puzzled. What was the situation that is causing you to troubleshoot the system?

Edit- On re-reading your post it seems your gauges were reading low. You say the stabilizer output was switching fast. At 12.6 V, with engine and gen not running, the stabilizer should be switching on/off about 1-2 times per sec. From your description, I suspect your stabilizer is defective, switching too rapidly and not putting out enough avg voltage.

Tom

Yes, it's a SIV. Both my temp and fuel gauges are barely moving. I would have to agree that it seems the stabilizer is not stabilizing. I can't think of anything else that would explain the test results. I did the tests with the engine off. The battery is in good shape, though. The fact that the gauges first climb to about 1/8 and then fall would seem to show that when juice is first applied they are climbing as they should and then when the stabilizer begins pulse, the needle falls. The pulses must not be on enough, as you suggest, to put out a significant output. I guess I'll try replacing this part. Thanks.

 

[Tom H]

Boob, What happens if you just run full 12.6 V to the gauges, bypassing the stabilizer? With the engine not running that should cause the gauges to read about 20% higher than they should, but at least that will tell you is the rest of the system is working correctly. Just put a jumper from B to I terminals. A paper clip might do. It will not cause any damage. For the Temp sender just pull the wire off the sender and put your 75 ohm resistor between the wire and ground. with full 12.6 V and 75 ohms, the Temp gauge should read a little above mid scale.

 

[Boobtube]

I'll try that. I also found a solid state stabilizer for 19 bucks(including shipping) so I'll throw that in when it arrives.

 

[Boobtube]

I placed the straight 12.6 volts to the fuel gauge with the 75 ohm resistor to ground. It read as you said, a little above mid scale (a tad below the 6 gallon mark on the gauge). That would seem to indicate the stabilizer has an issue. Thanks again.

 

[Tom H]

Make sure the solid state stabilizer you buy is the correct polarity. The original type are not polarity sensitive. I think your SIV now has neg earth. When all is resolved, I would like to look at your original stabilizer to see how / why it produces erroneous results.

Tom

 

[Tom H]

List, Boobtube installed a solid state stabilizer and that resolved his problems. AND he sent the stabilizer to me for testing. Indeed, I found it defective. It was stuck in the full ON position which puts full battery voltage to the gauges. I rapped on the housing with a screwdriver and it now behaves correctly, putting out the correct pulsing voltage and when hooked up to a pair of gauges they read correctly. BUT it seems likely that it may have been intermittently acting stuck open and closed. Nevertheless it seems a good idea that anyone who experiences problems with the original stabilizer might try just rapping on it with a screwdriver to see if that fixes the issue. Maybe unbolt it from the dash, rap it a few times, and then reattach it assuring a good ground .

Tom

 

[CRBASIN]

This is a very useful thread, and the document by Mike and Tom is even better. I used both to evaluate my temperature gauge accuracy.

I found the following, after testing grounds and the digital voltage stabilizer. The resistance and temperature at the thermostat housing are in line with the data in this thread and the Mike and Tom document, so I conclude that the circuit up to the gauge is ok. I then tested fuel and temp gauges by wiring them in series. The temp gauge seemed to be reading high according to this test.

Question: I ran the car up to 200 degrees per infrared thermometer and 45 ohms (by turning off the fan). The gauge moved into the red zone (see picture). Is the gauge reading high given that the WSM gives the operating range as 183-200 degrees? Should I adjust the gauge or leave well enough alone?

 

[hartmandm]

You might have two things at play here.
1. You mentioned that when wiring the two gauges in series with each other, the temperature gauge appears to read higher than expected. I assume you compared the temp gauge needle position against the picture in the document to conclude it is reading higher than it should. If that is the case, calibrating the gauge will help the gauge read more as expected.
2. You did a test where the infrared thermometer is reading 200 and the sender is providing 45 ohms. Something seems a bit off there. 200 degrees should correspond to around 52 ohms from the sender. 45 ohms corresponds to around 209 degrees. (Standard Motor Products specs indicate 43 ohms is 212 degrees). So either the thermometer is not seeing the same amount of heat as the sender is receiving, or the sender could be sending slightly lower resistances than it should.

Bottom line is that if you can correlate a given temperature in the coolant to what the gauge reads, then you know what your gauge should be reading when everything is working normal. When you see the gauge needle reading higher than expected, then you have a cause for concern. So you could just leave it all be.

P.S. - If you decide you want to calibrate the gauge, you need to remove the gauge from the car and you need a 10.0 / 10.1 V DC source and a way to provide the necessary resistance values. You can use a potentiometer to get the desired values. I've used this one: https://smile.amazon.com/gp/product/B00CQLN0WQ. It can handle the power requirements. Or I can sell you the set of 4 resistors needed for calibration. When the resistors are wired in series, the resistors provide the low, mid, 43 ohms (100C/212F) and high values. Probably a couple of bucks should cover the resistors + U.S. postal shipping (assuming you are in the US). I'd be happy to calibrate your gauge as well, but that would be more pricey, once you include round trip shipping and some nominal fee for the time to do the calibration.

Mike

 

[Tom H]

I have not previously seen a dial like yours, with no numbers on it. Comparing to the gauges I have seen, it looks like the red area starts at about 212 F (boiling) so it does look like it's reading higher than it should. But I would leave it alone. In my opinion it's more work than worthwhile to adjust. From your description it appears that normal running is well below the red. Just make a mental note that a little into the red is not really a problem unless it is occurring under "normal" driving conditions, which might alert you to a low coolant level, busted fan belt, etc.

When you tested by wiring the two gauges in series, you say the "temp gauge seemed to be reading high". I assume you mean the temp needle was higher up the dial than the Fuel gauge. That would indicate the Temp gauge is out of cal, but as noted above, not worth adjusting. Just adjust your interpretation instead.

Tom

 

[CRBASIN]

Thanks for your responses. At this point, I am inclined to leave the gauge alone but collect more data as time permits. I will try to take a picture of the fuel and temp gauges in "test" mode and "check my electrical scrap boxes for resistors. I will also try to measure the temperature at the water outlet a few more times. I am curious and I may have some time before classes start...

John

 

[loose_electron]

List, Boobtube installed a solid state stabilizer and that resolved his problems. AND he sent the stabilizer to me for testing. Indeed, I found it defective. It was stuck in the full ON position which puts full battery voltage to the gauges. I rapped on the housing with a screwdriver and it now behaves correctly, putting out the correct pulsing voltage and when hooked up to a pair of gauges they read correctly. BUT it seems likely that it may have been intermittently acting stuck open and closed. Nevertheless it seems a good idea that anyone who experiences problems with the original stabilizer might try just rapping on it with a screwdriver to see if that fixes the issue. Maybe unbolt it from the dash, rap it a few times, and then reattach it assuring a good ground .

Tom

Tom:

Burnt or corroded contacts are the issue here as you probably know. The original stabilizer used duty cycle tricks (fractional on and off) to get an approximate steady state voltage. This is how it was done back before transistors were widely used. Swapping in the solid state regulator is the smart way to go.

You can take the old beast apart and file and smooth (burnish them to a smooth surface) the contact faces to improve the reliability, but "solid state" is the way to go.

I would expect the "wack it till it works" method will give a temporary fix but the burnt contacts tend to stick again.

 

[Tom H]

Jerry, I would be inclined to agree. Especially if the issue was a critical issue. That's why I switched my ignition points to Pertronix. My suggestion to give the stabilizer a rap was mainly a more or less temporary one, and also a way to confirm that the stabilizer was indeed the issue. But then again, if that rap on the stabilizer keeps it running for another 50 years (or even 10 or 20) then maybe it's not so temporary. My Alpine still has the original and I have not had to rap it even once over the past 31 years and 30,000 miles I've driven it. Like you, I've spent my career in hi tech, but testing semiconductors, rather than designing them. But part of the kick I get out of my Alpine is enjoying how these "old designs" work. Ever see an old crank up Victrola that's been beautifully restored and listen to an old 78 playing through the horn? Sure, you can replace it with a modern digital stereo player but ??

Again, if the original stabilizer is a problem, the solid state replacement is the way to go. But ??

Best Regards,

Tom

 

[loose_electron]

Jerry, I would be inclined to agree. Especially if the issue was a critical issue. That's why I switched my ignition points to Pertronix. My suggestion to give the stabilizer a rap was mainly a more or less temporary one, and also a way to confirm that the stabilizer was indeed the issue. But then again, if that rap on the stabilizer keeps it running for another 50 years (or even 10 or 20) then maybe it's not so temporary. My Alpine still has the original and I have not had to rap it even once over the past 31 years and 30,000 miles I've driven it. Like you, I've spent my career in hi tech, but testing semiconductors, rather than designing them. But part of the kick I get out of my Alpine is enjoying how these "old designs" work. Ever see an old crank up Victrola that's been beautifully restored and listen to an old 78 playing through the horn? Sure, you can replace it with a modern digital stereo player but ??

Again, if the original stabilizer is a problem, the solid state replacement is the way to go. But ??

Best Regards,

Tom

Part of the fun can be keeping the old girl alive, just as it was done back in the day. Yeah I get it. My particular variant on a Sunbeam was already heavily modified once I got it so trying to go all original was not going to happen. No Victrola's in my collection but I do have several 5 tube radios, both Crosley and Atwater-Kent that I restored and still run with full vacuum tubes and 60Hz hum in the speaker.

 

[puff4]

I’ve got 5 restored Victrolas and Sonoras around the house... a former hobby of mine. Anyone want one?