M42club.com - Home of the BMW E30/E36 318i/iS

DISCUSSION => Electrical => Topic started by: bmwman91 on June 02, 2006, 11:54:42 AM

Title: Why 2 coolant temp sensors in head?
Post by: bmwman91 on June 02, 2006, 11:54:42 AM

Anyone know why there would be 2 coolant temperature sensors in the head (just below the intake manifold)?  Only one shows up in the Chilton's wiring diagrams, but there definitely are two there (as well as in the HTK).  And I know its not a switch for the auxillary fan, that is in the radiator.  Thanks.

PS
My guess is:  one for the motronic, and one for the temp gauge.

Title: Why 2 coolant temp sensors in head?
Post by: e9nine on June 02, 2006, 12:33:10 PM

Quote from: bmwman91

PS
My guess is:  one for the motronic, and one for the temp gauge.

Correct

Title: Why 2 coolant temp sensors in head?
Post by: tim_s on June 02, 2006, 01:34:45 PM

blue = motronic, brown = gauge

Title: Why 2 coolant temp sensors in head?
Post by: bmwman91 on June 02, 2006, 02:27:39 PM

Sveet.

One more sensor to test out for the datalogger.....

Title: Why 2 coolant temp sensors in head?
Post by: M42boy on June 02, 2006, 04:26:28 PM

I just replaced both of these, and they are REALLY cheap from Autohaus AZ.  Only thing is you really need to have the intake off to get good access to them.  Otherwise it's a PITA.

Mine were both working fine, but the plastic ends seem to get real brittle.  One of mine broke off with little to no resistance when I put a socket on it.  Definately use a wrench when tightening these vs. a socket.  Don't want to break the new ones!  

Yes, you are right as Tim and other have stated.  The Blue is the sensor, and the Brown is the sending unit for the guage.

Title: Why 2 coolant temp sensors in head?
Post by: bmwman91 on June 06, 2006, 12:11:11 AM

Well, I got the blue one out without incident, and without removing the manifold.  Recorded lots of temperature vs. resistance values and generated a best-fit curve for the sensor.  One more out of the way for my datalogger...