CHT VDO gauge problem

YOGIVW · Posted: Sun May 08, 2011 11:34 am Post subject: CHT VDO gauge problem

I just instaled brand new CHT VDO gauge and it odes not work. I connected it as instruction says and I am 100% sure that it is OK. The gauge reads all the time 140F connected to the sensor or not. Checked the sensor with multimeter and it looks it works, see video:

http://www.youtube.com/watch?v=lG92fisia58

but the gauge still reads the same. Is the gauge faulted? If yes, any chance to repair it or I need to buy new one?
_________________
Pawel
Vw 1303 1979 Black&Beige convertible
VW T4 2001 Caravelle Business 2.8 V6
Westfalia James Cook 2.9TD

AlteWagen · Troll Joined: February 23, 2007 Posts: 8503 Location: PNW

The last 3 VDO CHT gauges Ive installed had the wire colors backwards compared to the instructions. Flip the wires and I bet it works fine

Steve Arndt · Posted: Mon May 09, 2011 7:59 am Post subject:

As DLW said,
The + and - on the back of the gauge are labeled backwards on the three I have had. Flip them around.

pyrOman · Posted: Mon May 09, 2011 8:10 am Post subject:

FYI, just checked with my referrence book and on ALL thermocouples the RED wire is the negative, unlike any other wiring used elsewhere. VDO uses "J" type thermocouple wire which is red & white. Cool

_________________
Some people are so busy being clever they don't have time enough to be wise.

YOGIVW · Posted: Mon May 09, 2011 9:21 am Post subject:

just returned from my workshop and DLF you were right. I switched the wires, heated the sensor with the matches and it works Very Happy

Will put the sensor into boiling water to check it for accuracy. I wonder why the gauge shows 140F even if not connected? The outside temp was 68F.
_________________
Pawel
Vw 1303 1979 Black&Beige convertible
VW T4 2001 Caravelle Business 2.8 V6
Westfalia James Cook 2.9TD

Steve Arndt · Posted: Mon May 09, 2011 12:10 pm Post subject:

VDO uses a k type TC.
edit
http://www.omega.com/techref/thermcolorcodes.html

You are right as far as color goes!
But, I have made my own leads for the VDO gauge in the past and had identical readings with my own spool of red/yellow k type wire.

pyrOman · Posted: Mon May 09, 2011 1:12 pm Post subject:

AlteWagen · Troll Joined: February 23, 2007 Posts: 8503 Location: PNW

All the VDO gauges Ive sold over the last 8 years (more than 10) AND the 7 I own myself all have black and red harnesses.

The old man at North Hollywood Speedometer told me that VDO has not supplied real thermocouples in their kits for more than 10 years. The harness supplied is just regular non calibrated wire. I didnt believe him till I tried regular 14g wire to see if there was any difference, there was none!

Steve Arndt · Posted: Mon May 09, 2011 1:34 pm Post subject:

He isn't talking about the "extension harness wires" which are black/red and are standard copper wire. He is referencing the solid wire that is 1 foot long, that is the TC wire.

You must have posted right after I did.

pyrOman · Posted: Mon May 09, 2011 1:43 pm Post subject:

AlteWagen · Troll Joined: February 23, 2007 Posts: 8503 Location: PNW

So you are talking about the actual "sender" with the ring on it? All of mine were colorless and had a clear material surrounding the wire itself which seems to wear quickly.

Steve Arndt · Posted: Mon May 09, 2011 1:54 pm Post subject:

It looks like you are correct.

VDO exhaust pyrometer uses K type,
VDO CHT gauge uses J type.

I am now running a dakota digital and matching k type.

This guys page is outdated with the wrong TC info:
http://www.ratwell.com/technical/VDOGauges.html#cht

pyrOman · Posted: Mon May 09, 2011 1:54 pm Post subject:

If you peel the insulating "cover" of the thermocouple you will see the white and red wires indicating a "J" type. The ring is prolly made of copper too as it is a good heat conductor. I do not use the ring on 2 of my motors so I remove the ring, twist the bare ends together and place it on the #3 exhaust flange. Does read a bit hotter but I use it as referrence anyway. Also, for the sake of removing all possibility of wire "error", I run thermocouple wire all the way to the gauge instead of regular copper wire. Razz

_________________
Some people are so busy being clever they don't have time enough to be wise.

Steve Arndt · Posted: Tue May 10, 2011 8:21 am Post subject:

While you are at it running the TC wire all the way to the gauge, run a couple extra pairs.

I have my Tech Edge WB02 logging three TCs, and a fourth hooked to the dash gauge.

I bought a partial spool of k type wire on ebay cheap.

Steve

YOGIVW · Posted: Fri May 13, 2011 4:03 pm Post subject:

I put the sensor into boiling water and it showed 260F Confused

Any chance to correct it?
_________________
Pawel
Vw 1303 1979 Black&Beige convertible
VW T4 2001 Caravelle Business 2.8 V6
Westfalia James Cook 2.9TD

AlteWagen · Troll Joined: February 23, 2007 Posts: 8503 Location: PNW

YOGIVW · Posted: Sat May 14, 2011 12:38 am Post subject:

pyrOman · Posted: Sat May 14, 2011 5:57 am Post subject:

pyrOman · Posted: Sat May 14, 2011 8:22 am Post subject:


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