Ok so after dealing with these beauties today here is what I found.
Thee 1710511 (yellow plug) sender has been superseded by the 1710512 (black or brown plug). Apparently this one is common with the E36 chassis?
Here are the differences that I have found, the 511 sender might be calibrated to a 24 volt systemm based on the marking on its casing. Apparently the 512 is calibrated to a 12v system. This could explain the reason why the 511 reads ~2x the temperature, ei resistance, for a given temperature compared to the 512 unit. Interestingly the sender lowers its resistance with temperature. I was expecting an increase in resistance. So the higher the temperature the lower the resistance, thus on a 12 v system it would read a lower than expected resistance for a given temperature thus indicating a 2X the temp reading of the 512 sender.
Just posting this for your reference / information. I replaced the DME reference (2 pronged) sender while chasing the hot start issue I have been experiencing a very intermittent as in 2 weeks per occurance when the ambient temp is ~mid 70 to mid 80ish degrees and the car has let cool down for about 1 hr - 2hrs. Since I was replacing the DME ref sender I figure I replaced the coolant gauge sender as well... Well Bavauto sent the 512 unit for the coolant gauge sender since the 511 is discontinued. So the gauge apparently is calibrated to the 511 sender and the middle mark is ~90C while first white mark ~75C. These two data pts where based on e30 tech forum postings.
When using the the 512 sender the gauge indicated one needle width to the left of the 1 first white mark ~75C (I am using a 71C thermostat). I have come to expect it to reside halfway between the first white mark and the middle mark based on the readings from the 511 sender with the 71C thermostat. Apparently it is just a different sender calibration. I will take some readings using an infrared thermoter of the thermost housing and the hoses to get an idea of where the coolant temperature is and also obtain a better calibration of my gauge and sender combination.
For comparison, a buddy of mine is running the 71C thermostat on his M30 big 5 sedan with the same yellow plug 511 sender and his needle reads the same range as mine. Folks on E30 Tech are quoting stock gauge readings a needle width to the left of the first gauge mark with the 71C thermostat and middle mark to somewhere in between with the 80C thermostat...
Thee 1710511 (yellow plug) sender has been superseded by the 1710512 (black or brown plug). Apparently this one is common with the E36 chassis?
Here are the differences that I have found, the 511 sender might be calibrated to a 24 volt systemm based on the marking on its casing. Apparently the 512 is calibrated to a 12v system. This could explain the reason why the 511 reads ~2x the temperature, ei resistance, for a given temperature compared to the 512 unit. Interestingly the sender lowers its resistance with temperature. I was expecting an increase in resistance. So the higher the temperature the lower the resistance, thus on a 12 v system it would read a lower than expected resistance for a given temperature thus indicating a 2X the temp reading of the 512 sender.
Just posting this for your reference / information. I replaced the DME reference (2 pronged) sender while chasing the hot start issue I have been experiencing a very intermittent as in 2 weeks per occurance when the ambient temp is ~mid 70 to mid 80ish degrees and the car has let cool down for about 1 hr - 2hrs. Since I was replacing the DME ref sender I figure I replaced the coolant gauge sender as well... Well Bavauto sent the 512 unit for the coolant gauge sender since the 511 is discontinued. So the gauge apparently is calibrated to the 511 sender and the middle mark is ~90C while first white mark ~75C. These two data pts where based on e30 tech forum postings.
When using the the 512 sender the gauge indicated one needle width to the left of the 1 first white mark ~75C (I am using a 71C thermostat). I have come to expect it to reside halfway between the first white mark and the middle mark based on the readings from the 511 sender with the 71C thermostat. Apparently it is just a different sender calibration. I will take some readings using an infrared thermoter of the thermost housing and the hoses to get an idea of where the coolant temperature is and also obtain a better calibration of my gauge and sender combination.
For comparison, a buddy of mine is running the 71C thermostat on his M30 big 5 sedan with the same yellow plug 511 sender and his needle reads the same range as mine. Folks on E30 Tech are quoting stock gauge readings a needle width to the left of the first gauge mark with the 71C thermostat and middle mark to somewhere in between with the 80C thermostat...