Guage testing and adjustments

Dana67Dart · May 19, 2022

As some of you know I fried my temp gauge when my mechanical IVR lost the heater wire full volting the temp and fuel gauge.

It still functions, but normal operating temp is just at the low tick of the temp gauge, normally it would be 1/4 past the low tick.

(Note: the temp gauge is 67 so the normal range is shifted to the right)

Luckly the fuel gauge functions as expected.

EDIT--
I have been collecting clusters to gather good working gauges. So far I have I really good used, 2 less than great but functional, and I lucked in on a NOS temp gauge.

To date I have 4 clusters and one NOS Temp gauge.

all 4 clusters have snap on speedo cables so none of them are 67.

2 of them have the shifted temp "normal" ranges. I don't know what year the shifted "Normal" became centered.

End EDIT----

I have another cluster inbound and it looks promising.

I figured I would test the used gauge assuming the NOS gauge is the most accurate.

I set up a series of 100w resisters and a series of 18 awg jumper cables.

I can do any resistance from 1 ohm to 100 ohms.

I have a 12v power supply and an rt-eng.com IVR4 limiter.

I set up the gauges and resisters etc.

Actual resistance values below, the input voltage to the IVR was 13.66v

10.4 ohms
17.3 ohms
18.3 ohms
23.4 ohms
73.5 ohms

10 ohms NOS

10 ohms Used

23 ohms NOS

23 ohms used

73 ohms NOS

73 ohms used

NOS no voltage (cold, 5 minutes)

Used no voltage (cold, 5 minutes)

Here is the interesting thing...

23 ohms has been the defacto 1/2 gauge resistance value. As you can see the 23 ohm readings were around 1/3 reading.

17 to 18 ohm caused half gauge reading

18 ohms NOS

18 ohms used

My conclusion is the used gauge is about as accurate as it can be.

I had messed with the upper and lower limits in the past and had no idea where it should read.

I started with adjusting the high limit and got it on the line when 10 ohms was applied.

Then I adjusted the low limit and got the needle on the line with 73 ohms

I then went back and forth, high and low, adjusting one affected the other till I got a happy medium.

Now both gauges read about the same.

It will be interesting to see how the incoming cluster works out.

Either way I have 2 options to replace my bad gauge.

CFD244 · May 19, 2022

Thanks for the testing and results. Good info here. :thumbsup:

Dana67Dart · May 19, 2022

There will be a few ohms additional resistance from the wire in the car, 55 year old connections and the like.

67Dart273 · May 19, 2022

A few ohms in wire is not going to affect much, unless there is "a few more" ohms at the connections---the sender (and don't forget ground, fuel), the kick panel connector (fuel gauge), the bulkhead connector (oil and temp) the cluster harness connector --including possible bad PC board pins, the IVR CONTACT FINGERS IN THE CLUSTER (solder jumpers across), and the nut connectors at the gauges to the PC board.

Also don't forget cluster ground, which must be "same as battery"

67Dart273 · May 19, 2022

While you are screwin around why don't you spend 35 and buy that gauge compensator I posted and see how they do? Cheaper than MeterMatch.

Fuel Sender To Gauge Converter Module Ohm Adjust To any Sender To Gauge | eBay

Dana67Dart · May 19, 2022

67Dart273 said:
While you are screwin around why don't you spend 35 and buy that gauge compensator I posted and see how they do? Cheaper than MeterMatch.

I'll be happy to do some testing on it if you send me one.

My fuel sender is OEM and reads really accurite. I need to lower the pickup to get the last 2 gallons

Dana67Dart · May 21, 2022

I received the Cluster I was expecting Thursday. Here is the results of those gauge tests.

What I found interesting is both of these gauges were 1/2 way at 23 Ohms where the NOS and the other gauge was 18 at 1/2 way.

Maybe the proper way to calibrate these gauges is to make them accurate at 1/2 scale by shifting the needle that direction with proper voltage and resistance applied by making the high and low readings wider and shifted?

Below tests were done with the same set up as the first post.

Temp Gauge no power

73 Ohms (Temp)

23 ohms (Temp)

18 ohms (temp)

10 ohms (temp)

No Power Fuel

73 ohms (fuel)

23 ohms (fuel)

18 oms (fuel)

10 ohms (fuel)

Dana67Dart · May 21, 2022

just for grins I did 9 ohms on the fuel gauge

Dana67Dart · May 21, 2022

Here are some photos of the misc. gauges I have collected. Note the faceplate part numbers and the back of the gauges. some are the same some are different

another

Another

Note the holes on the back of this gauge are reversed from the previous two

Another
Centered Temp "Normal" range (NOS gauge)

NOTE:
The photos in my first post show a shifted "Normal" face plate on the loose NOS gauge and a center "Normal" on the Used loose gage. Prior to testing I swapped the face plates between the two as I expected to use the NOS gauge in my dash and needed the shifted "normal"

In the photos below I used the photo of the correct face plate for the NOS and the correct faceplate for the used gauge.

I know, just trying to keep you all on your toes!

Dana67Dart · May 21, 2022

The gauges the loose face plates are off of

Note the white plastic insulator and this one must have been off of another car or earlier year as the needle is different shape and color

Another

Note the white plastic insulator and this one the heater wire came off of the left stud

Dana67Dart · May 21, 2022

This one had a black insulator that was cracked and fell apart when I took it out of the cluster,

the rest of the gauge looked great.

I'm still trying to figure out why some of the adjustment holes are on the left while others are on the right. My first thought was one side was fuel and the other side was temp, but I don't know. might just be later years or different manufacturer.