Temp. Gauge Sending Unit & TCS Switch

[Rick B.]

I have a few questions for those knowledgeable in this area !

I have read that some inaccuracies can be caused by Teflon tape and other thread sealants being applied to these devices.

1) Is this true, and if so what is recommended to be placed on the threads prior to installation ?

2) Is there a "more" accurate replacement temp. gauge sending unit available out there? I had read earlier threads about a "Wells TU 5" but no idea where there are available, how to identify them or even if they are different than the replacement units sold at various Corvette internet parts stores.

Any advice would certainly be appreciated !

Thanks !!!

Rick

[Patrick H.]

Re: Temp. Gauge Sending Unit & TCS Switch

Question #1: nothing, nada, zip. Be sure the threads in the head are clean, and just tighten the sender(s) in place.

Question #2: I highly suspect you will find it's "hit-or-miss" on this one.

Patrick

[Rick B.]

Re: Temp. Gauge Sending Unit & TCS Switch

Thank you !
That's kinda what I thought I would find out.
But I am still curious.....if the units rely on internal resistance then what effect would applying thread sealants have on them?
I could understand if they were piezo-electric and you put an excessive amount of teflon tape or something to really snug it up and cause some sort of distortion to the unit when it is finally torqued/tightened up.
But otherwise....?
So is this part a myth or is it true?

[Patrick H.]

Re: Temp. Gauge Sending Unit & TCS Switch

Thank you !
That's kinda what I thought I would find out.
But I am still curious.....if the units rely on internal resistance then what effect would applying thread sealants have on them?

You isolate them from ground.
Teflon = electrical barrier = no circuit = no worky.

[Rick B.]

Re: Temp. Gauge Sending Unit & TCS Switch


Ahhhh, that's it ! Completely simple but yet couldn't figure it out !
Thanks again !
Rick

[Ernie F.]

Re: Temp. Gauge Sending Unit & TCS Switch

It’s hit or miss with the TU5 but in reality it is hit or miss with any sending unit.

I’ve been testing temperature gauges for the past two months and have tested over one hundred dash units! Original NOS gauges and used originals to try to achieve some sort of relative scale that is accurate for most year cars instead of relying on the old GM scale I’ve posted on many forums and threads.

With over one hundred gauges tested the results were quite disturbing.

A case and point to this would be four NOS gauges tested. We tested two brand new GM 1961-1962 temperature gauges, (two tested) the required ohms to reach 180 on the gauge was 96. On two NOS 63 units, the required ohms were 117 and 128. So in theory the TU5 might work on one gauge or the other but not for all!

Another example would be the 240 temperature mark on the 62 and 63 – 64 gauges. On the 62 test units one required 62 ohms, the second one required only 75. On the two 63 test units one required 43 ohms and one required 68.

Now these are brand new original gauges and as you can see quite a bit different in the required input!

The same discrepancies held true for other gauges tested over different years at different temperature levels. On multiple instances two a like gauges from the same year car required different ohms input to achieve the proper reading.

This might help explain the hit or miss with the TU5 which when tested repeatedly delivers a pretty consistent ohms output scale.

Another issue is in testing of the sending units. While most brands are pretty close in the output at the set temperatures, most will vary on the upward side compared to the output on the downward side while testing. In most cases you will find on the upper temperature scale a 5-10 ohm difference in the output from going up to coming down where on the lower scale it is much wider ranging from 11-20 ohms. Most of the sending units I tested and plotted on a chart rose and fell at petty much the same scale. (Except for the new GM sending unit which is a complete waste of money)
This coincides with the fact that the hotter the car the fewer the margin for error you have with the ohms input and the colder the car the more the margin for error.

Is there an answer this problem! Well only partially! As I’ve preached on other forums and on the CPRL thread over the years adding resistance is not the answer to calibration of a dash unit. If you add resistance to allow the dash unit to read correctly at 180 degrees it will only be accurate at this fixed temperature and no where else. The temperature gauges unlike the fuel gauge is not a linear gauge!

The only way you will ever achieve a matched set is to find out the fixed ohms output of the sending unit and match it to the dash unit. This can be done but is very tedious.

Ernie

[Rick B.]

Re: Temp. Gauge Sending Unit & TCS Switch

Thank you for the detailed response Ernie !
I am interested in learning more on this subject, so I guess I'll have to do some more searching on past threads and read up.
Did you find any similarity between resistance readings (anticipated ranges) when you compared C2 to C3 sending units as they were different part numbers if I recall?
The reason I ask is that I still have my proper/original functioning temp. sending unit off of my 72 however any new replacement one I might choose to get now would be the pin style. If I knew what range it should be within I could verify its' accuracy, as I currently have no idea how far out it may or may not be at present.

Thanks, Rick

[Patrick H.]

Re: Temp. Gauge Sending Unit & TCS Switch

Thank you for the detailed response Ernie !
I am interested in learning more on this subject, so I guess I'll have to do some more searching on past threads and read up.
Did you find any similarity between resistance readings (anticipated ranges) when you compared C2 to C3 sending units as they were different part numbers if I recall?
The reason I ask is that I still have my proper/original functioning temp. sending unit off of my 72 however any new replacement one I might choose to get now would be the pin style. If I knew what range it should be within I could verify its' accuracy, as I currently have no idea how far out it may or may not be at present.

Thanks, Rick

Rick,

Why are you replacing your original from your 72? Is it no longer functioning?

Patrick

[Ernie F.]

Re: Temp. Gauge Sending Unit & TCS Switch

Thank you for the detailed response Ernie !
I am interested in learning more on this subject, so I guess I'll have to do some more searching on past threads and read up.
Did you find any similarity between resistance readings (anticipated ranges) when you compared C2 to C3 sending units as they were different part numbers if I recall?
The reason I ask is that I still have my proper/original functioning temp. sending unit off of my 72 however any new replacement one I might choose to get now would be the pin style. If I knew what range it should be within I could verify its' accuracy, as I currently have no idea how far out it may or may not be at present.

Thanks, Rick

The range of the sender should correspond to the test subject dash units.

The issue is making sure the sender matches the dash unit.

In one tested dash unit I received the following readings and this was for a 1971 original dash unit and the only info I have here for your gauge. (The rest of he data is at my office).

Required ohms for test gauge T102.

Gauge Mark=Ohms req.
100=200 ohms
1st Mark=109 ohms
210=79 ohms
2nd Mark=65 ohms
250=51 ohms

Keep in mind before you jump to testing, this was a used original dash unit. I have the gauges out of my 70 right now and I have not tested them yet and I have data for other gauges at my office for similar cars of like gauges. I took pictures of the test and the results with the gauge sitting on the paper so I would not loose them. But I only have a few copies of these at home.

Ernie

[Ernie F.]

Re: Temp. Gauge Sending Unit & TCS Switch

To create a dash testing unit you need a potentiometer (pot) that will adjust from 0 to at least 450 ohms. You can use three 150 ohm wire wound pots linked in a series to create an adjustable resistance of 450 ohms.

Once you introduce adjustable resistance to test circuit, move the pots until the desired gauge reading is achieved. Remove the wire feeding the dash unit from the gauge and test the resistance (Ohms) required to achieve this reading. Then move on to the next mark on the gauge in the same manner.

Once you establish the correct input required for the dash unit you then move to the sending unit for testing.

There are other factors in this including the condition of the gauge and the amount of oil remaining inside the pindle housing. If this oil is dried up of coarse it will require a different amount of ohms to allow for accurate movement.

This is one reason we tested original NOS gauges where we had them to test.

Ernie

[Rick B.]

Re: Temp. Gauge Sending Unit & TCS Switch

Patrick, I hadn't completely decided to change out the sending unit yet, but as I had taken great care to restore the engine I couldn't bare the thought of having to possibly replace the sending unit just after I dropped the engine back into the compartment. I was always somewhat suspicious of the accuracy of the gauge, but in all honesty that may have more to do with the fact that I had been aware for some time that others had experienced problems. Personally I have no evidence to believe that the gauge and/or the sending unit are inaccurate in my car at this time and will probably try to verify the temp. using an IR temp. gun.
Ernie, I now see what you mean about it being a tedious venture. There are obviously many factors at play here, and any combination could cause varying results.
Nonetheless the information you've given me is fantastic and at the very least I can better appreciate the reason(s) behind some of the potential discrepancies we hear about.

Rick