Dash gauges - accuracy?
02-28-2003, 08:47 AM
#1
Racer
Thread Starter
Dash gauges - accuracy?
Question(s).
1) My voltmeter is about 1v low on the dash. (ie. 14v at bypass terminal, 13 on dash). Can it be calibrated.
2) Temp never shows much above the lowest white mark. Up to the 2nd at best. Is it just normal for these cold blooded animals to run cool, or, my imagination? I would say that the engine gets warm by feel, but never "hot". (and sure I know its winter).
Thanks,
Bob
1981 928
1) My voltmeter is about 1v low on the dash. (ie. 14v at bypass terminal, 13 on dash). Can it be calibrated.
2) Temp never shows much above the lowest white mark. Up to the 2nd at best. Is it just normal for these cold blooded animals to run cool, or, my imagination? I would say that the engine gets warm by feel, but never "hot". (and sure I know its winter).
Thanks,
Bob
1981 928
02-28-2003, 09:59 AM
#2
Rennlist Member
Rennlist Site Sponsor
There are a LOT of connections between the battery and the voltmeter on the dash. The low reading may well be caused by the cumulative losses of each of these connections.
There is usually an adjustment pot on the back of the voltmeter. You can remove the pod, clean and treat each of the connections, especially those for the flexible circuit board, and then use an accurate voltmeter to tweak the dash unit. This may or may not get you the same readings as the system voltage - but what is the true system voltage? Battery terminal? Jump start terminal? You may discover that the dash voltmeter is reading precisely the voltage presented to it. Do you want to adjust the voltmeter to read battery voltage regardless of voltage losses in the system?
Many of our owners are concerned because their temp gauges go to the third line. Some points to ponder:
The instruments are not lab instruments, they are indicators to show possible problems.
There are no easy to intrepret numbers on the gauge - you have no idea of what the gauge is telling you.
The acceptable temp range for the engine is actually pretty wide. The coolant temp should be around 85 - 90 deg C most of the time. In very cold weather, it may not get that high, if you are pulling as much heat as possible out of the heater, and are in slow traffic where the engine is not really generating much waste heat. At the other extreme, it may go higher in the same slow traffic in the summer, when you are dumping heat into the system with the A/C, instead of taking it out with the heater.
To me, your gauge reading sounds normal for the conditions.
There is usually an adjustment pot on the back of the voltmeter. You can remove the pod, clean and treat each of the connections, especially those for the flexible circuit board, and then use an accurate voltmeter to tweak the dash unit. This may or may not get you the same readings as the system voltage - but what is the true system voltage? Battery terminal? Jump start terminal? You may discover that the dash voltmeter is reading precisely the voltage presented to it. Do you want to adjust the voltmeter to read battery voltage regardless of voltage losses in the system?
Many of our owners are concerned because their temp gauges go to the third line. Some points to ponder:
The instruments are not lab instruments, they are indicators to show possible problems.
There are no easy to intrepret numbers on the gauge - you have no idea of what the gauge is telling you.
The acceptable temp range for the engine is actually pretty wide. The coolant temp should be around 85 - 90 deg C most of the time. In very cold weather, it may not get that high, if you are pulling as much heat as possible out of the heater, and are in slow traffic where the engine is not really generating much waste heat. At the other extreme, it may go higher in the same slow traffic in the summer, when you are dumping heat into the system with the A/C, instead of taking it out with the heater.
To me, your gauge reading sounds normal for the conditions.
02-28-2003, 05:32 PM
#3
Burning Brakes
Join Date: Jan 2003
Location: Minneapolis MN
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Wally P. Always on it. Yeah, what he said...
FWIW, my tmep gage stays right in the middle between the lines 99% of the time, but if I just sit and idle for 45 min. or so (in Minneapolis Road Construction Season a.k.a. summer Traffic Jams)it will creep to he top line and stay there for maybe 20 min. Then the electric fan comes on and seems to hold it there. Once moving again, the temp needle goes right back to center in about 2 min. Seems like it should be better than that, but these things seem to have a "hot" rep.
The heater will draw the needle down, and I usually turn it on in traffic jams just as a precaution. - Ruf
FWIW, my tmep gage stays right in the middle between the lines 99% of the time, but if I just sit and idle for 45 min. or so (in Minneapolis Road Construction Season a.k.a. summer Traffic Jams)it will creep to he top line and stay there for maybe 20 min. Then the electric fan comes on and seems to hold it there. Once moving again, the temp needle goes right back to center in about 2 min. Seems like it should be better than that, but these things seem to have a "hot" rep.
The heater will draw the needle down, and I usually turn it on in traffic jams just as a precaution. - Ruf
03-04-2003, 11:35 PM
#4
6th Gear
Join Date: Mar 2003
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I have a problem with the fuel gauge and the voltage gauge. I removed the instrument cluster and found that most of the nuts on the gauges were lose. after tightening and checking all connections I found that the volt guage agreed with my volt meter. I also found that the fuel gauge was fixed. a week later I left the car out in the cold overnight and the fuel gauge is worse than ever!!!! I just live with it.
81 928
Harold
81 928
Harold
03-05-2003, 08:41 AM
#5
Burning Brakes
Join Date: May 2001
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Harold,
Your flaky fuel gauge could be the sending unit in the top of the tank. You can pull it and clean it and perhaps get a better gauge reading. Be very careful with the fine wires running along its length. The sending unit on my 78 was totally gunked up and the float wouldn't fall below 3/4. Your float could be getting 'hung' up on the corrosion.
I also found my volt gauge is much better on both the 78 and the 84 after t-belt, accessory belts. I figure the alt. belt was too loose in both cases. Now both read 13-14 with nothing on and fall to just over 12 with lights, tunes, heater, etc.
Your flaky fuel gauge could be the sending unit in the top of the tank. You can pull it and clean it and perhaps get a better gauge reading. Be very careful with the fine wires running along its length. The sending unit on my 78 was totally gunked up and the float wouldn't fall below 3/4. Your float could be getting 'hung' up on the corrosion.
I also found my volt gauge is much better on both the 78 and the 84 after t-belt, accessory belts. I figure the alt. belt was too loose in both cases. Now both read 13-14 with nothing on and fall to just over 12 with lights, tunes, heater, etc.