Coolant temp gauge replacement (late petrol)

[itchyfeet]

What resistance were you seeing from the sender when you stopped the engine ?

161 Ohms, there is more to the sensor than meets the eye I think, it can't behave as a resistor.

[937carrera]

I think I would be moving from bench test in the van to bench test in the kitchen. Quicker and cheaper to boil the kettle.

You have another sender that was giving 165 ohms at @ 90 degrees (an assumption, maybe get your thermocouple out), use that for the bench test, alongside the fixed value resistors. I think you have 51 ohm resistors so 3 of those in series will do for a more controlled comparison test. (left this in, I was writing while you replied above)

Have you also thought of using say a 200 ohm resistance, connecting it and leaving for 10 minutes or so to see if that also flicks the LED on, in case it is in some way related to operating time for the gauge ?

I've looked at the wiring diagrams, and there doesn't seem to be any other components involved, except for a diode between current tracks 31 & 32, I would have thought you would have other issues if that had failed though

Just chucking some more thoughts out there for you, for when you've finished remodelling the wall.

[AngeloEvs]

I thought you were using the guage that you repaired but since the new gauge appears to work fitted into the dash pod there is no point in testing it removed.

Just as a point of reference, I looked at your pic, are those 1/4W carbon resistors being used as dummy loads?

Should have noticed you had two vans, Carrera's post alerted me to that. I would swap the dash pods, save a lot of time and they are pretty robust unless you are concerned that the copper strips in the 14 way connector are on their last legs.

[itchyfeet]

You have another sender that was giving 165 ohms at @ 90 degrees (an assumption, maybe get your thermocouple out)
.

just put that in the van

Have you also thought of using say a 200 ohm resistance, connecting it and leaving for 10 minutes or so to see if that also flicks the LED on, in case it is in some way related to operating time for the gauge ?
.

I have left a 100R for 10 mins it does not go higer than LED

I've looked at the wiring diagrams, and there doesn't seem to be any other components involved, except for a diode between current tracks 31 & 32, I would have thought you would have other issues if that had failed though
.

yes that's what I'm thinking some other components needed.

[AngeloEvs]

The temp sender is more or less a resistor but the insulation can break down. A multimeter might not show that either due to the low voltage/current being output.

[937carrera]

Just had a look at Bentley 90.21 again.

The test procedure references using the VW1301 tester using values of 50 and and 510, equivalent to 34 and 265 ohms. Given the widespread use of this special tool it does not appear that its function is anything but a variable resistor ??

[itchyfeet]

I thought you were using the guage that you repaired but since the new gauge appears to work fitted into the dash pod there is no point in testing it removed.

Just as a point of reference, I looked at your pic, are those 1/4W carbon resistors being used as dummy loads?

Should have noticed you had two vans, Carrera's post alerted me to that. I would swap the dash pods, save a lot of time and they are pretty robust unless you are concerned that the copper strips in the 14 way connector are on their last legs.

0.4W 51 R RS 164-126 using two in series.

Lets say I swap the tin top dash into the this van ( pop top) and it works what does that tell me?
Or if I swap this duff dash into the tin top van and it does not work what does that tell me?

There has to be more to the circuit I have two gauges behaving exactly the same

last test for the night 80 degree should be in the middle of gauge
P1100615 by Paul_Barr, on Flickr

[itchyfeet]

The temp sender is more or less a resistor but the insulation can break down. A multimeter might not show that either due to the low voltage/current being output.

tried a brand new one and got the same

[itchyfeet]

anybody got a dash specific wiring schematic?

[937carrera]

Lets say I swap the tin top dash into the this van ( pop top) and it works what does that tell me?

It tells you that the wiring and sender in the pop top is fine, issue is in the dash

Or if I swap this duff dash into the tin top van and it does not work what does that tell me?

It confirms that the issue is in the dash as the problem travels with the dash

[itchyfeet]

Surely I have proven it's the dash, as in the last picture I'm not even connected to the vehicle so it does not help me solve the fault.

There is something missing from the circuit.

[AngeloEvs]

If you put the dash under test into the tin top van and it works then you can concentrate on the coolant sender and associated wiring. You can disregard the level sender part of the system because by removing module 43 you have isolated that entire part of the coolant warning system.

If, on the other hand, the fault continues to show when fitted in the tin top then the fault is in the dash.

The temp gauge current at 50 ohms is going to be high enough to cause those carbon resistors to get hot and affect their resistance but that is not the main issue regards your temp gauge.

That gauge, at 80 degrees is sitting too far to the right, the sender resistance at 80 degrees is much lower than it should be, or the incorrect type or the gauge is faulty, incorrectly calibrated, etc.

[937carrera]

OK, you are probably recording more stuff than you are posting, so others are not necessarily seeing the whole picture

How do you know that the gauge in the picture is working correctly. You have done a kitchen test at a value which makes absolute sense, but not done the tests included in Bentley. What was the actual resistance of the sender at 79 degrees

How do you know that the sender in the picture is working correctly. Do you know what it should read at 80, other than the earlier advice that 100 ohms corresponds to about the middle of the gauge.

If I was with my van I would go and take some measurements for comparison, but I'm not so I can't, sorry

On the other component front, you may be correct, but I haven't seen anything (including in the test procedures and Bentley diagnostic tree) that would indicate that there actually are other components.

You have two gauges and two senders, Are they both behaving the same for the same test conditions ? If they are that's a good indication that the components are good, but not definitive.

[itchyfeet]

You have two gauges and two senders, Are they both behaving the same for the same test conditions ? If they are that's a good indication that the components are good, but not definitive.

yes two gauges one in dash one out
both behave the same with fixed resiistors and both behave the same with both sensors

but sensors behave different to.fixed resistors

one sensor old one new.

[itchyfeet]

What is the purpose of the capacitor?
its not fitted in my guage out of dash test.
coincidence?