Temperature Gauge Not working

Rek

Rek

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I have spliced the engine harness from the E34 Alpina B10 into my car. Everything works (eventually) except the temperature gauge and fuel gauge. The fuel gauge I can discount from haveing a faulty sender.

The Temperature gauge is a different matter.

Earth the Brown and White gauge wire produces the full effect, so not the gauge. The sender was not sending any signals on resistance test so that was replaced.

My sender has two wires coming from it. One brown and yellow and one brown and violet. My diagram says the brown and violet has the resistance and the other goes to earth, however SFDon whom I would trust above all else says the brown and yellow should be connected to the dash gauge.

I've tried both and nothing works. The fit of the sender wires is not great but there is continuity in the wires and a connection.

Does anyone have any ideas which might help? I am shaking down the car after a rebuild and can't afford an overheating engine.
 
The gauge reflects voltage in the circuit. The sender is a variable ground. The sender is designed to vary the ground in the circuit; when the engine is cold the sender allows very little voltage to flow; as the engine warms to normal operating temperature, the sender provides a better ground, allowing an amount of current flow that enables the gauge to show the needle at 3 o'clock. If the temp rises above normal operating range the sender allows a full current flow and the needle on the gauge goes to max deflection.

My car only has a single temp sender, but I think you may be able to use the same part I used. Last year, I replaced my original sender with a VDO aftermarket sender, and it works exactly as the BMW sender would work. (I was guessing that BMW would not redesign a part that worked well for years across multiple manufacturers). If you installed a gauge like this one, it would enable the gauge to function (I presume the other terminal on your sender is for a warning light). If you go to a single pole sender you will be able to avoid overheating your new engine by watching the gauge, but you won't have a light.

I believe this is the sender I used (but VDO makes a couple of metric senders -- you need to check the diameter of the opening for the sender to get the right size for your car): https://www.vdo-gauges.com/sensors/...ature-sender-250-deg-f-120-deg-c-m14x1-5.html

Again, this sender is wired to the gauge.

One other thing. I am confused by your description of the diagram. The sender should not need a ground because it is attached to the engine and could easily be designed to ground through the body. Mine is designed this way. Secondly, most of the ground wires on our cars are brown. Your diagram shows a multi color wire being grounded, which I have not seen.
 
Ohmess said:
The gauge reflects voltage in the circuit. The sender is a variable ground. The sender is designed to vary the ground in the circuit; when the engine is cold the sender allows very little voltage to flow; as the engine warms to normal operating temperature, the sender provides a better ground, allowing an amount of current flow that enables the gauge to show the needle at 3 o'clock. If the temp rises above normal operating range the sender allows a full current flow and the needle on the gauge goes to max deflection.

My car only has a single temp sender, but I think you may be able to use the same part I used. Last year, I replaced my original sender with a VDO aftermarket sender, and it works exactly as the BMW sender would work. (I was guessing that BMW would not redesign a part that worked well for years across multiple manufacturers). If you installed a gauge like this one, it would enable the gauge to function (I presume the other terminal on your sender is for a warning light). If you go to a single pole sender you will be able to avoid overheating your new engine by watching the gauge, but you won't have a light.

I believe this is the sender I used (but VDO makes a couple of metric senders -- you need to check the diameter of the opening for the sender to get the right size for your car): https://www.vdo-gauges.com/sensors/...ature-sender-250-deg-f-120-deg-c-m14x1-5.html

Again, this sender is wired to the gauge.

One other thing. I am confused by your description of the diagram. The sender should not need a ground because it is attached to the engine and could easily be designed to ground through the body. Mine is designed this way. Secondly, most of the ground wires on our cars are brown. Your diagram shows a multi color wire being grounded, which I have not seen.
Click to expand...


Thanks for this input. I may have to try the single point temp sender which you describe.

The wiring diagram for the sender is attached. As far as I can see the BR/VI wite goes to the dash and the BR/GE goes to ground, somewhere in the dash.

Screen Shot 2017-05-10 at 08.48.29.png
 
Circling back to my earlier suggestion -- one thing that may be a problem is the connection between the temp sender and the ECU. If the ECU uses temperature as a parameter to alter fuel mixtures, for example, lacking this input the ECU may assume the car is always running at start up temp (cold). This would obviously be far less than optimal. I am speculating here (my car has carburetors), but thought I would mention this.

If I had to guess how to wire this from looking at your wiring diagram, I would try wiring the Br/VI to both the ECU and to the gauge, and I would ground the BR/GE wire to the same ground used for the gauge.

If that doesn't work, post how you did your "resistance test." My sender would have a fair amount of resistance when cold, and the resistance decreases as the sender is heated (by the coolant in the car). Not sure if yours works this way, but it is such a well defined process that it likely does.
 
Many thanks for your help. I have connected the Br/Vi wire to the gauge and the BR/GE wire to the same gauge as an earth. I will heat the car up tomorrow and find out the results.

The resistance test I conducted was to contact the two pins of the sender and measured the resistance, it being about 2000 ohms and once I heated this up, it went way down. It did indicate that it was alive, especially as it was new. The old gauge did not register - just 1 on the multi-meter.

For the gauge itself, I grounded the wire and it flicked to the top. The internet tells me that the gauge is working but I am no expert. So.....watch this space.
 
Sounds like you are making progress. As I noted above, the gauge merely reflects voltage in the circuit. That is why the gauge deflects fully when you directly ground it.
 
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