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Temp Gauge testing at home
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crazyvwvanman
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PostPosted: Fri May 13, 2011 4:17 pm    Post subject: Temp Gauge testing at home Reply with quote

This test resistor info is for verifying that the gauge electrics work. If you have a situation where your gauge is reading outside the expected norm, this test will help determine if the dash gauge system is at fault. Once you determine that the gauge system is working ok, that leaves a problem with the sender or with the engine temps. The idea is to restore confidence that the dash gauge is working right and that the warning led triggers at the appropriate sender input level. Then you can concentrate any additional efforts where they are needed, like in the engine compartment.


The temperature gauge can be tested at home by anyone with a pack of 100 ohm resistors from Radio Shack that cost about $1 for the 1/2watt 100 ohm in a 5 pack.

This is done by connecting a resistor and certain combinations of them to the wire(s) that goes to the gauge temp sender in the thermostat housing. In this way you can verify that the gauge needle responds with the right readings for several important resistances. The wire(s) must be unhooked from the temp sender for this test. Then the resistor is connected between the yellow/red wire and ground. Just touching the metal firmly together with your fingers is enough. It takes a full minute for the gauge needle to stop moving so you may want a helper to watch the gauge while you firmly hold the resistor ends to the gauge wire and to ground. With a 2 wire sender 1 wire is ground, the brown wire. On these you touch the 2 resister legs to the 2 pins in the connector. Below are the various resistances for testing, along with the gauge needle position expected and what engine condition it would normally indicate.

200 ohms = needle just beginning to register over first white area (engine pretty cold still)

100 ohms = needle near but not yet reaching the led (engine warming up)

67 ohms = needle over some part of the led (normal engine running temp)

50 ohms = needle above the led by about 2 needle widths (engine hotter than you like to see, led not flashing yet)

33 ohms = needle at the last white mark (engine very hot with temp warning led now flashing)

You can create all the above resistances with 1, 2, or 3 of the 100 ohms. depending on how they are arranged. See photo below.


Image may have been reduced in size. Click image to view fullscreen.



First, before connecting any resistors, unplug the wire(s) from the gauge temp sender, turn on the key, and measure the voltage on the yellow/red wire, between it and ground. You must have 10 volts or very close to it. If not, something else is wrong and the resistor test won't give very valid results. If it is a 2 wire sender, measure between the 2 wires. If not very near 10 volts it could be a problem with the brown ground wire so try measuring just the yellow/red and bare metal ground somewhere. If it reads 10 volts that way finish the testing that way but come back and fix the ground so the gauge can work right.

Of course you can buy other resistor values and combine them differently to get the same ohms as above for testing. Also, most volt meters are also ohm meters so you can measure the combinations for yourself if you need reassuring that the combination gives the ohms it is supposed to. These resistors are not perfect so expect the readings to be off by an ohm or two. The test meters are not perfect either so those will vary slightly also. An ohm or two doesn't matter for this testing.


I will probably add to and modify this when I have more to say or show.

Mark


Last edited by crazyvwvanman on Sat May 14, 2011 9:07 am; edited 1 time in total
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BillM
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PostPosted: Fri May 13, 2011 6:31 pm    Post subject: Reply with quote

Mark helped me trouble shoot my gauge awhile back using them above information. I just want to add that it took me purchasing various brands/sources of sendors to get one that would work correctly. Their values were all over the place. It's also a good time go point out that adding a resistor to overcome a problem is wrong. It will interfere with the proper operation of the blinking red light. That red light has saved more than one of
Of my motors.

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r39o
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PostPosted: Fri May 13, 2011 7:05 pm    Post subject: Reply with quote

What values for the fuel gauge?
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crazyvwvanman
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PostPosted: Fri May 13, 2011 7:25 pm    Post subject: Reply with quote

Fuel gauge according to Bentley is 33 ohms full, but empty varies by year. I have not verified this myself, or done much testing of the fuel gauge at all. Maybe someday.

Mark


r39o wrote:
What values for the fuel gauge?
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Summers420us
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PostPosted: Sat May 14, 2011 8:11 am    Post subject: Reply with quote

200 ohms = needle just beginning to register over first white area (engine pretty cold still)

100 ohms = needle near but not yet reaching the led (engine warming up)

67 ohms = needle over some part of the led (normal engine running temp)

50 ohms = needle above the led by about 2 needle widths (engine hotter than you like to see, led not flashing yet)

33 ohms = needle at the last white mark (engine very hot with temp warning led now flashing)

Mark this is awesome but what are the actusal temps that correspond with these readings? That would be helpful as well. Thanks for posting. Can't wait to test!
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crazyvwvanman
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PostPosted: Sat May 14, 2011 8:56 am    Post subject: Reply with quote

This test resistor info is for verifying that the gauge electrics work. If you have a situation where your gauge is reading outside the expected norm, this test will help determine if the dash gauge system is at fault. Once you determine that the gauge system is working ok, that leaves a problem with the sender or with the engine temps. The idea is to restore confidence that the dash gauge is working right and that the warning led triggers at the appropriate sender input level. Then you can concentrate any additional efforts where they are needed.

Mark

Summers420us wrote:
.................

Mark this is awesome but what are the actusal temps that correspond with these readings? That would be helpful as well. Thanks for posting. Can't wait to test!
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Witless Joe
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PostPosted: Sat May 14, 2011 12:32 pm    Post subject: Reply with quote

Mark, that was a great public service to type all that out!

I bought a resistance decade box several years ago, which is a much more expensive (although much more convenient) way to perform this test.

r39o wrote:
What values for the fuel gauge?

Ohms for the fuel gauge (and temp gauge) are found in this thread:

http://www.thesamba.com/vw/forum/viewtopic.php?p=1304488&highlight=#1304488

Quote:
What it comes down to is: ("tool" means VW1301 tester dial setting)

tool = 50 ----- 35ohms (tank reads full, temp reads hot)
tool = 320 ---- 210ohms (tank reads empty)
tool = 510 ---- 340ohms (temp gauge reads cold)"

There is a two-pin connector for the fuel tank sender under the dash, and you can tap your test resistors in there, turn on the ignition key, and bob's your uncle.

BTW, it's good to double-check your resistors with an ohmmeter. I was surprised how far out some of them are relative to their advertised value.
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PostPosted: Sat May 14, 2011 1:06 pm    Post subject: Reply with quote

Witless Joe wrote:
r39o wrote:
What values for the fuel gauge?

Ohms for the fuel gauge (and temp gauge) are found in this thread:

http://www.thesamba.com/vw/forum/viewtopic.php?p=1304488&highlight=#1304488

Quote:
What it comes down to is: ("tool" means VW1301 tester dial setting)

tool = 50 ----- 35ohms (tank reads full, temp reads hot)
tool = 320 ---- 210ohms (tank reads empty)
tool = 510 ---- 340ohms (temp gauge reads cold)"

There is a two-pin connector for the fuel tank sender under the dash, and you can tap your test resistors in there, turn on the ignition key, and bob's your uncle.

BTW, it's good to double-check your resistors with an ohmmeter. I was surprised how far out some of them are relative to their advertised value.

I should have known this was discussed before.....duh.

I want to edit this thread to make it topic specific and reference in the FAQ.

ANY BODY HAVE A PROBLEM WITH MY PUTTING MY MOD HAT ON AND TAILORING THIS THREAD TO BE TOPIC SPECIFIC?????
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crazyvwvanman
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PostPosted: Sat May 14, 2011 2:20 pm    Post subject: Reply with quote

I think it would be great if the gauge testing info was better developed and easier to find. My concern with the fuel gauge numbers is that in the Vanagon Bentley there are different fuel gauge test values given for different years.

Page 90.5 has values for 80-84

Page 90.20 has different vaules for 85+

The values are the settings of the VW 1301 test tool. The conversion to ohms as I have been led to understand is to take the 1301 setting, divide that by 2, then add 10, to get ohms.

There is also an online reference for translating 1301 tester setting into ohms. I will add it when I locate it again.

Since I have not done any resistance testing of the Vanagon fuel gauge I think it would be good to do so before posting it too broadly. Maybe someone else has a few clusters from different years to check what resistors will do what.

Mark


r39o wrote:

I should have known this was discussed before.....duh.

I want to edit this thread to make it topic specific and reference in the FAQ.

ANY BODY HAVE A PROBLEM WITH MY PUTTING MY MOD HAT ON AND TAILORING THIS THREAD TO BE TOPIC SPECIFIC?????
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gflater
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PostPosted: Sat Aug 04, 2012 10:18 pm    Post subject: Reply with quote

Summers420us wrote:
200 ohms = needle just beginning to register over first white area (engine pretty cold still)

100 ohms = needle near but not yet reaching the led (engine warming up)

67 ohms = needle over some part of the led (normal engine running temp)

50 ohms = needle above the led by about 2 needle widths (engine hotter than you like to see, led not flashing yet)

33 ohms = needle at the last white mark (engine very hot with temp warning led now flashing)

Mark this is awesome but what are the actusal temps that correspond with these readings? That would be helpful as well. Thanks for posting. Can't wait to test!


I was playing around with this as I wanted to use this information for my Subaru conversion. I am mostly interested in getting the trigger point for overheating on the LED.
The subaru sensor, from what I understand makes the needle read higher than the VW since its resistance drops earlier/faster than the VW sensor.

I think I fried my temperature gauge, I wanted to start with a 150 Ohm resistor.
I accidentally put my multi meter in diode/continuity check mode when I turned on the ignition and I think that shorted the gauge internally.

Interestingly the LED reacts to the coolant level wire being grounded (no LED) when the wire is open, LED blinks after about 30 seconds after initial blink.

The needle stays down regardless of the resistor I tried, and I read no voltage over the resistor Sad

Are there any circuits outside the gauge that could have fried?
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67SingleCabGuy
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PostPosted: Sun Aug 12, 2012 10:52 am    Post subject: Temperature Gauge Ohm Testing Reply with quote

First I want to say thank you very much for sharing with everyone this ohm test information.

I hope its OK if I post my results in this thread to get some feedback. I started a thread
about my temperature gauge showing it was running very hot although the temperatures I got
when testing the different components in the cooling system with an IR gun showed normal results.

Leading me to change the thermostat and temp sender twice with the same results.

Finally today I had time to test the gauge with the method mentioned in this thread.

I first tested the volts at the wires going to the sender. Came in normal at 10.17 Volts.

Below are the Ohm values and pictures where my temp gauge is pointing to.
In my opinion it seems to be running a tad above normal in some cases.
I'm just trying to get other opinions to make sure its the gauge.
Thanks

200 Ohms (Picture below) - In the middle of white area. Needle a little high???

Image may have been reduced in size. Click image to view fullscreen.


100 Ohms (Picture below) - 1/2 covering LED. Needle a little high???

Image may have been reduced in size. Click image to view fullscreen.


67 Ohms (Picture below) - Just below second dot from the top. Needle seems high???

Image may have been reduced in size. Click image to view fullscreen.


50 Ohms (Picture below) - Covering second dot from top (This is where my needle stays when I run the van and the fan cycles on and off). Needle seems high???

Image may have been reduced in size. Click image to view fullscreen.


33 Ohms (Picture below) - Covering last white mark with LED flashing. This one seems normal.

Image may have been reduced in size. Click image to view fullscreen.


Any expert opinion would be appreciated as I'm trying very hard to get to the botttom of my high temp gauge reading when running.

Thanks a bunch.
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crazyvwvanman
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PostPosted: Sun Aug 12, 2012 11:40 am    Post subject: Re: Temperature Gauge Ohm Testing Reply with quote

I would say your gauge reads a tad high, by less than a needles width. This does not explain why "my temperature gauge showing it was running very hot". There is probably some other problem besides the gauge or you are expecting too low of a reading. Maybe you can explain what you mean by "running very hot"?

Mark



67SingleCabGuy wrote:
.... I started a thread
about my temperature gauge showing it was running very hot although the temperatures I got
when testing the different components in the cooling system with an IR gun showed normal results.

Leading me to change the thermostat and temp sender twice with the same results.

Finally today I had time to test the gauge with the method mentioned in this thread.

I first tested the volts at the wires going to the sender. Came in normal at 10.17 Volts.

Below are the Ohm values and pictures where my temp gauge is pointing to.
In my opinion it seems to be running a tad above normal in some cases.
I'm just trying to get other opinions to make sure its the gauge.
Thanks....
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67SingleCabGuy
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PostPosted: Sun Aug 12, 2012 12:23 pm    Post subject: Reply with quote

Mark,

Thanks for the reply.

Below is a picture of my temperature gauge with the van running, getting up to normal operating temperature. Fan cycles, and temp readings are normal using an IR gun.

Image may have been reduced in size. Click image to view fullscreen.


Here is the thread I started about the problem.

http://www.thesamba.com/vw/forum/viewtopic.php?t=522960

That is what I mean about the gauge showing that it is running hot although the IR gun seems to show otherwise. Hence why I used your method to test the gauge.

Thanks
Kevin
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PostPosted: Sun Aug 12, 2012 12:45 pm    Post subject: Reply with quote

Perhaps you could measure the resistance at the sender when it is this hot -- that could help point to the gauge or the sender or to a real problem.
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crazyvwvanman
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PostPosted: Sun Aug 12, 2012 1:24 pm    Post subject: Reply with quote

Yes, when the van is running your temp needle is riding a lot higher than I would be happy about. I don't agree that your IR temp reading are necessarily normal. Did you try dropping water on the heads as suggested?

First, I would point out that the large hose going to the top of the thermostat is the RETURN hose, bringing cooled coolant FROM the radiator, so measuring that hose isn't much of an indication of engine temp. In our VW engines the thermostat directly lets cooled coolant back into the engine, while in some other engines the thermostat directly lets hot coolant out like many people assume.

Second, the radiator fan runs when the radiator temp switch tells it to. It can cycle on/off apparently normally while the engine burns up, if there is not enough circulation. The coolant has to have reasonable circulation flow from the engine to the radiator and back in order for the engine to be at the desired temp. That is mostly the job of the thermostat but it assumes the radiator has good flow and not much trapped air at the top.

Third, your photos showed only the top of the thermostat but there is a smaller lower disc that plays a role in closing off the bypass circuit as the engine warms up. It is common for FLAPS to sell an Audi version of the thermostat that has the wrong size lower disc. Do you have any photos of the complete thermostat by itself?

Mark


67SingleCabGuy wrote:
.....Below is a picture of my temperature gauge with the van running, getting up to normal operating temperature. Fan cycles, and temp readings are normal using an IR gun.
......................
That is what I mean about the gauge showing that it is running hot although the IR gun seems to show otherwise. Hence why I used your method to test the gauge.

Thanks
Kevin
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PostPosted: Sun Aug 12, 2012 2:20 pm    Post subject: Reply with quote

If your needle is reading high with the resistors, it is time to measure the output voltage of the voltage regulator at the back of the instrument panel.
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PostPosted: Sun Aug 12, 2012 2:24 pm    Post subject: Reply with quote

He already mentioned measuring the voltage on the wires that plug into the temp sender. With key on and the connecter unplugged that wire(s) shows the voltage from the instrument cluster voltage regulator. He said he got 10.16v IIRC.

Mark

stevey88 wrote:
If your needle is reading high with the resistors, it is time to measure the output voltage of the voltage regulator at the back of the instrument panel.
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PostPosted: Sun Aug 12, 2012 3:05 pm    Post subject: Reply with quote

crazyvwvanman wrote:
He already mentioned measuring the voltage on the wires that plug into the temp sender. With key on and the connecter unplugged that wire(s) shows the voltage from the instrument cluster voltage regulator. He said he got 10.16v IIRC.

Mark

stevey88 wrote:
If your needle is reading high with the resistors, it is time to measure the output voltage of the voltage regulator at the back of the instrument panel.


Sorry, missed that. If both wires to the temp gauge reads 10.16V with the plug at the sensor removed, then the temp gauge need to be re-calibrated in his case.
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crazyvwvanman
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PostPosted: Sun Aug 12, 2012 3:07 pm    Post subject: Reply with quote

Some of his readings are slightly at the high end but the 33 ohm test shows the needle between the 2 high temp calibration dots, the tiny white dots. There are 2 mechanical adjustments inside the gauge but these only adjust the high and low temp set points. The actual adjustments are tricky but are used to calibrate the gauge set points to VW 1301 Resistance Tool settings, per the Bentley. The Bentley shows the analog clock version of the gauge rather than the tach version that has the tiny dots. In any case the allowable variation for gauge testing is plus or minus 1 needle width from ideal center. Looking at his 33 ohm reading the needle is well within allowable. Looking at his adjacent gas gauge you can see the same sets of tiny calibration dots.

Here is his photo he labeled as from his 33 ohm test.

Image may have been reduced in size. Click image to view fullscreen.


Below is a link to Bentley and their conversion values from VW 1301 Test Tool setting to actual ohms.

My tests were done with resistors and I did not try a resistor value that matched the low temp reading. It would be easy enough to do with 5 of the 100 ohm resistors I used at the top of this thread. By combining the 67 ohm set in series with the 200 ohm set you would get pretty close to the value VW used for the colder reading of the gauge.

http://www.bentleypublishers.com/tech/vw/bentley.vw1301.testing.htm


Mark


Last edited by crazyvwvanman on Sun Aug 12, 2012 3:11 pm; edited 1 time in total
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PostPosted: Sun Aug 12, 2012 3:10 pm    Post subject: Reply with quote

Ahwahnee wrote:
Perhaps you could measure the resistance at the sender when it is this hot -- that could help point to the gauge or the sender or to a real problem.


Not sure if this will clear anything up, but I did run the Bus as recommended and measured the ohm resistance at the 2 prongs of the sendor when the needle was pointing to different locations on the gauge.

155 - Needle in Middle of LED
140 - Needle just above and not touching LED
94 - Covering second dot from top of gauge
93-95 - Needle at point in picture, fan cycling on and off, measured 3 different times

As mentioned I did get a Wahler thermostat part number 025.121.113F
I had the original VW stamped thermostat I took out and before I put the new one in I compaired all sizes as I also thought this might be the problem.

Does the Ohm reading seem correct, and the gauge possibly bad?
I guess I would say the ohm reading with the fan going on, which I would assume is when the gauge should be in the middle but is at the second dot from the top.

Thanks
Kevin
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