Thermofan Thermostat - what doesn't work...
Posted: Sat Dec 29, 2007 9:13 am
Ok - so my electromechanical Thermofan thermostat died, the capillary tube fractured at the bulb leaving me to fish it out of the top hose
So what about an electronic one, with some decent adjustment for set point and differential ? Easy.
But I didn't want to add another sensor so why not tap into the EFI block sensor ? To cut a long story short its not really practical.
Issues :
The signal is around 400mV at operating temp with only a few mV change over the temperature area of interest - so getting a small differential was proving very difficult.
And the big one - the reference voltage applied to the sensor is not stable enough - it fluctuates by a few tens of mV with changes in battery / alternator voltage causing unpredictable cut in and out.
So don't waste you time - just add a separate sensor.
For the tech minded the EFI system really only uses the block temp sensor for cold start and warmup - once its up to temp its pretty well ignored which explains the low sensitivity at operating temp.
The temp gauge sensor is also no good as the system works on a different principle.

So what about an electronic one, with some decent adjustment for set point and differential ? Easy.
But I didn't want to add another sensor so why not tap into the EFI block sensor ? To cut a long story short its not really practical.
Issues :
The signal is around 400mV at operating temp with only a few mV change over the temperature area of interest - so getting a small differential was proving very difficult.
And the big one - the reference voltage applied to the sensor is not stable enough - it fluctuates by a few tens of mV with changes in battery / alternator voltage causing unpredictable cut in and out.
So don't waste you time - just add a separate sensor.
For the tech minded the EFI system really only uses the block temp sensor for cold start and warmup - once its up to temp its pretty well ignored which explains the low sensitivity at operating temp.
The temp gauge sensor is also no good as the system works on a different principle.