How to check accuracy of temperature gauge at the roadside

[AngeloEvs]

The VAG calibration test uses a 100 ohm resistor from the guage to earth (with sender disconnected). The needle should sit + or - one needles width of centre. Mine sits slightly left when using this test. Vag use a small test box with various resistors in it and a rotary selector switch and use it to check the calibration of the fuel and temp gauges. A 47 ohm resistor is used to confirm that the coolant LED functions when an over temperature is reached. The resistors need to be at least 1/2 watt as they get pretty warm while the gauge meanders its way to the rest point.

If your VAN has the LSCU in the relay box it is easy to test the gauge calibration. Let me know if you want details and pics. Unfortunately, AOL have closed all member WEB sites so I cannot refer you to mine as it has hit the dust but I still have all the info.

[Bond007]

I would love some more info on this please

My temp guage hasn't worked properly for the last 6 months.

Had the instrument cluster out today expecting to find corrosion on the connectors, but everything looks as it should be.
Sometimes the red light flashes for a while and the needle moves, then the light goes out and the needle drops, so it's definately those damned electric gremlins

Sorted the milometer out though

[AngeloEvs]

Assuming no loss of coolant, the coolant led will flash if the resistance in the coolant level sender circuit is high or if the resistance in the temperature sender circuit is very low. See the schematic and wiring colour codes below.

[img:410:496]http://muchos.co.uk/members/Evangeluse/sch90v3.jpg[/img]


A lot of checks can be made at the LSCU (level Sender Control Unit) that is located in the fuse box and looks like a relay (usually in position 3 from left). However, on pre 86 models it's somewhere else. The following applies for post 86 1.9ltr WBX'r though it may apply to a lot of other nmodels but I cannot confirm this.

You can test the calibration of the gauge by removing the LSCU and inserting the resistor as shown below but first disconnect the temperature sender. I prefer to disconnect the T7 connector (that lives in the black box in the engine bay see picture) rather than fiddle about under the van and disturbing the Cab facing connector on the thermostat housing. The pins show where to measure the coolant temperature sender resistance if you want to check it. The resistance is usually around 100 ohms for a normal temp hot engine.


[img:500:375]http://muchos.co.uk/members/Evangeluse/sockett790.jpg[/img]


I fit male spades on the end of the resistor then insert the resistor into the vacant sockets (see picture). Before doing this I recommend that you check that the lower connection (marked Earth) is actually going to earth. It terminates at the cluster next to the fuse box. A meter is the best way of doing this but a visual inspection could suffice. Insert the 100 ohm resistor and switch the ignition on, then wait for the needle to stop climbing. Inserts a 47 ohm resistor to test that coolant LED over temp is working using the same method.


[img:350:195]http://muchos.co.uk/members/Evangeluse/socket.jpg[/img]

[img:350:318]http://muchos.co.uk/members/Evangeluse/res90.jpg[/img]

[syncrosimon]

If you want to test the temp gauge, run the vehicle as hard as you dare for as long as poss, like up a steep hill, then allow to idle, watch the temp gauge, it should go just past the red dot, perhaps a needle width or two, then the fan should come on on the radiator, and bring it down to just below the red dot. If it does, all is well.

(this obviously assumes the radiator and thermoswitch are working)

(and assumes you can get the engine hot enough)

If it is not spewing water all over the place around the engine at this temp then it is another good sign.

Dont be shy, and test it good and proper.

[lloyd]

Nice write-up AngeloEvs.

Maybe Wiki it??

HarryMann is our Wiki guru.