Coolant temp gauge replacement (late petrol)

[itchyfeet]

Mine doesn't work on the pop top, never has, previous owner had a 52mm VDO temp gauge fitted and it appears to run off the original sender ( it looks like a standard sender)
The VDO always reads 80 degC and only shuffles a few degrees past when very hot so not a great indication.

I checked the tracks buzzed out so must be the gauge, petrol gauge works fine so I assume not regulator

I sourced a replacement from somebody on here and fitted it today, pics as ususal

Looks like almost a perfect instrument molding....

P1100521 by Paul_Barr, on Flickr

but it's not...looks melted very odd...

P1100522 by Paul_Barr, on Flickr

4 screws out

P1100524 by Paul_Barr, on Flickr

remove nuts and washers

P1100525 by Paul_Barr, on Flickr

hinge it out and remove clock hands and face

P1100529 by Paul_Barr, on Flickr

it pulls out

P1100530 by Paul_Barr, on Flickr

Replacement fitted, I was feeling please with myself until I got this after 5 to 10 mins, any ideas?
Fuel tank is genuinely full I filled it today

P1100536 by Paul_Barr, on Flickr

[itchyfeet]

any suggestions as to what is wrong?

Replacement fitted, I was feeling please with myself until I got this after 5 to 10 mins, any ideas?
Fuel tank is genuinely full I filled it today

P1100536 by Paul_Barr, on Flickr

[morr]

If the level sensor in your coolant bottle if faulty, or it's associated wiring (and relay on some models), or if you are low on coolant the led will flash, and on certain years it will also cause the gauge to go to max.

[itchyfeet]

If the level sensor in your coolant bottle if faulty, or it's associated wiring (and relay on some models), or if you are low on coolant the led will flash, and on certain years it will also cause the gauge to go to max.

mmm interesting, thanks the low coolant light didn't flash even with the plug disconnected with old gauge and still does not will 'new gauge'
I wonder if i pull the relay what happens, test for tomorrow.

I tested a spare sensor in freshly boiled water ( probably 90 degrees once The sensor had taken time to warm up) and got about 165 Ohms so this gives me a rough idea of what the resistance should be so I can play with a fixed resistance.

P1100542 by Paul_Barr, on Flickr

I then conncted the sensor dierect to gauge ( bypassing all the other level sensor wiring as the wire is cut just before dash) the gauge rose to about 3/4, not quite so high but may indicate the level sensor is part of the problem.

So it got me thinking I wonder if they are adjustable....

hello what are these holes with notches ??

P1100543 by Paul_Barr, on Flickr

So out with the drill and drill and punch out rivets ( need a steady hand they are tiny)

Hard to see but it does look like they are adjustable, probably why every bodies gauges are different.

Out of time tonight I look more tomorrow

P1100544 by Paul_Barr, on Flickr

[itchyfeet]

anybody happen to know which pin is 10V, which is ground and which is sender to save me pulling the dash out?

P1100525 by Paul_Barr, on Flickr

[CJH]

Left to right in your photo:
10v - GND - Sender

[itchyfeet]

Left to right in your photo:
10v - GND - Sender

You're a star thanks Chris.

[AngeloEvs]

The gauge is adjustable. A 100 ohm resistor across the temp gauge output with a 10v supply should see the needle about a needle width left of the led. VAG test allows for plus or minus one needle width

The circuit and associated components are for the LED and has a small micro chip. The chip is responsible for causing the LED to flash. To test the gauge out of the dash simply connect the 100 ohm resistor across the output to the centre nut and connect a 10v DC supply across the input and centre nut with the negative to the centre nut. The LED should flash for a few seconds and then stop. The needle will slowly rise to the point left of the led.

Do not be tempted to use a 9V battery, the LED will flash continuously.

[itchyfeet]

The gauge is adjustable. A 100 ohm resistor across the temp gauge output with a 10v supply should see the needle about a needle width left of the led. VAG test allows for plus or minus one needle width

The circuit and associated components are for the LED and has a small micro chip. The chip is responsible for causing the LED to flash. To test the gauge out of the dash simply connect the 100 ohm resistor across the output to the centre nut and connect a 10v DC supply across the input and centre nut with the negative to the centre nut. The LED should flash for a few seconds and then stop. The needle will slowly rise to the point left of the led.

Do not be tempted to use a 9V battery, the LED will flash continuously.

thanks, I have an adjustable bench psu so can get 10V, this gauge does not work but I can pkay and see if its something simple.

I will try a 100 ohm on the other gauge in the van tomorrow by passing the level sensor.

Do you know where the 100 ohm test is defined?

[AngeloEvs]

Bentley manual. VAG use a resistance box and select various values for fuel and temp gauge tests along with tolerances. I found that a value of 100 ohms matches that of a temp sender at normal operating temp and places the needle one width left of the LED. I have tested quite a number of gauges and 100 ohms gives the most reliable test.

[MidLifeCrisis]

Any chance that you are using a temp switch rather than a temp sensor - that might explain why the gauge went hard over after 5 minutes?

[itchyfeet]

Any chance that you are using a temp switch rather than a temp sensor - that might explain why the gauge went hard over after 5 minutes?

Unlikely becuse it's black, all the switches I have seen are blue, it would have moved over much faster I think with a short to ground but worth checking, thanks for the idea.

[itchyfeet]

Bentley manual. VAG use a resistance box and select various values for fuel and temp gauge tests along with tolerances. I found that a value of 100 ohms matches that of a temp sender at normal operating temp and places the needle one width left of the LED. I have tested quite a number of gauges and 100 ohms gives the most reliable test.

Thanks I had a quick skim through bentley and didn't see it, I really must sit down one day and spend some time looking through.

[itchyfeet]

I then conncted the sensor dierect to gauge ( bypassing all the other level sensor wiring as the wire is cut just before dash) the gauge rose to about 3/4 [ in a cip of freshly boiled water], not quite so high but may indicate the level sensor is part of the problem.

Thinking again if the gauge is 115 range ( its printed on it) and 87 thermostat temp is roughly at the LED then 3/4 would be roughly 100 so looks to me like the level sensor is to blame.

[AngeloEvs]

The 'level' sensor or the 'temperature' sensor? You can isolate the level sensor to check if it is faulty by removing the module 43 (in the fuse box on later vans), In the event of low coolant or a wiring, sensor fault, etc, module 43 will output negative pulses that trigger the circuit in the temp gauge and then the LED flashes. Module 43 itself can become faulty and cause temp gauge problems.

The best way to check the gauge and all other functions is to remove the dash and bench test it. Like you say, isolating all the wiring and other hardware eliminates other possible causes.