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Date:         Mon, 27 Aug 2001 21:56:40 -0500
Reply-To:     All of Us <weber@OWC.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         All of Us <weber@OWC.NET>
Subject:      Re: Temperature Gauge
Comments: To: Edgt1000@AOL.COM
Content-Type: text/plain; charset="iso-8859-1"

Ed:

I just got done diagnosing some problems I was having with my cooling system. I had just done a drain, flush, and refill on the system and it was running hotter than before I started. Turned out the new thermostat I had also installed wasn't opening, but one of the things I tested before I threw out a brand new thermostat was the gauge to see if it was the culprit. In Bentley they say to use some special VW tool to test the gauge. Well you can make your own for about $2.00.

Basically the gauge works on the varying resistance signal provided by the temperature sending unit (TSU). The hotter the TSU gets the less resistance it produces. The only problems you can have with the system are a bad TSU, a bad gauge, or a bad voltage regulator in the dash. I guess you could also have a broken wire or a loose connection but I assume you don't have those problems because you are getting some reading.

Anyway, the test procedure is in section 90.21 in Bentley, you do have one, don't you? You will need a digital volt meter (DVM) that reads DC voltage and ohms resistance to do the testing. First test the voltage regulator in the dash to see if it is producing between 9.5 and 10.5 volts DC. 10.0 is perfect but anywhere in that range is OK. If the VR is OK then its time to check the gauge. Bentley indicates that 510 ohms of resistance should place the needle on the temp gauge at the bottom edge of the white painted "cold" zone on the gauge. And that 50 ohms should put the needle on the hot line at the top of the gauge and should start the LED flashing.

To perform this test you unhook the connector from the TSU and use a potentiometer to provide a measured amount of resistance to the gauge. I went to Radio Shack and bought a 5k ohm potentiometer for $1.99 plus tax. I soldered 2 wires to the leads and crimped a male pan type connector onto the other end of the wires. You use your DVM to measure the resistance and turn the dial on the potentiometer until it reads either 510 ohms or 50 ohms. Then you plug the pan connectors on the potentiometer into the connector that you unhooked from the TSU. Turn on the key and see where the needle stops. If it lands in the aforementioned location or 1 needle width high or low the gauge is OK for that resistance. Disconnect the potentiometer and reset it to the other resistance figure using your DVM. Plug it back in and see where the needle lands this time. Again, 1 needle width high or low is OK. If the gauge checks OK and the VR is also OK then just cough up the $10-$15 that VW wants for a replacement TSU and o-ring because its the only thing left that could be bad and Bentley has no procedure to test it. Hope this helps you out. If you have any questions let me know.

Dan Weber Miss Blue - '87 GL Weekender

----- Original Message ----- From: Ed Nieves. <Edgt1000@AOL.COM> To: <vanagon@GERRY.VANAGON.COM> Sent: Monday, August 27, 2001 7:50 PM Subject: Temperature Gauge

> My temperature gauge in my '90 vanagon gl is not working properly, I think. > It stays a little past the 1/4 white zone. The fan still kicks in when warm > but the needle doesn't reach the half way mark. The red light doesn't come > on. Change termostat but still the same. I need some advise. Thanks. > > Ed > Orlando, FL > '90 Vanagon GL - Red >


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