Just Tested the Blue coolant temp sensor

[marty325]

Hey guys,
My 325i has been a bit sore on petrol lately (18 mpg) so i've checked all the usual suspects, tps, icv, fuel pipes, and all rubber boots. Everything seems in order except for the Blue coolant temp sensor, it's reading a resistance of 4.7k ohms when cold and 0.48k ohms when hot. From what ive read on here it should be 3 to 4k when cold and 0.33 ohms when warm. Is the difference in what mine is reading enough to cause the mpg to drop significantly?

Many thanks.

[marty325]

car is a 91 H reg 325i sport by the way

[Brianmoooore]

Hot resistance seems a bit high. Should be more like 0.33k (not 0.33 ohms!).
Are you sure the car is getting up to correct running temp?
Where did you measure the resistance of the sensor? It should be done at the ECU plug, especially on a M20.

[marty325]

Hot resistance seems a bit high. Should be more like 0.33k (not 0.33 ohms!).
Are you sure the car is getting up to correct running temp?
Where did you measure the resistance of the sensor? It should be done at the ECU plug, especially on a M20.

Sorry 0.33k ohms, unplugged the sensor lead and measured accross the terminals on the sensor, does it need to be measured at the ecu under the dash? if so which pins? Car was ran for 15 mins so should have been up to running temp.

Cheers,
Marty

[richy187]

according to the Bentley manual Blue temperature sensor resistance values are:

-10 deg C 7-11.6 k Ohms
20 deg C 2.1-2.9 k Ohms
80 deg C 0.27-0.4 k Ohms