First off it's not a SE, it will be a Zetec-E, this engine is completly different from the SE and is fitted to the 1.4 and 1.6 varients.

From experience the Focus fans rarely come on, I have only ever had them come on a hot day when stuck in heavy traffic and even then it was not until I was nearly out of it.

In any case the fans should only activate when this is insufficent natural airflow, i.e when in traffic, they should never come on whilst moving, they should activate when you switch the A/C on.

The Focus has a CHT which on your model is screwed into the back of the cylinder head, nearest the timing belt end and below the inlet manifold, it is NOT on the thermostat housing, this provides info on temperature to the ECU and also the temp gauge and also activates the fans in turn if hot enough.

A little bit of geek info as well here, if it gets to hot it has an over heating strategy where by it will shut fuelling off to two cylinders and so allow them to act as air pumps and thus save further heat output, so if you get a loss of power don't worry it's not something else thats wrong, I guess you haven't hit that high a temp yet otherwise you would have experienced this.

I do agree though thermostat (Stuck closed) or fans depending on whether you were stuck in traffic etc at the time.

Martin