I seem to be having the same problems as others.  The coolent seems to
be going somewere, and I also seem to be getting poor MPG.

When I bought the car in November, an N reg 306 TD Sedan, I replaced
the thermostat and rad cap, flushed the radiator and filled the system
using a header bottle on the rad.  I seem then, over time, to be
getting airlocks in the system.

On using the header bottle and getting rid of the airlocks, the temp
gauge shows a steady 80C, then over a period of about 7-10 days it will
progressively get lower and lower when running until it hangs steady at
just above 70c.  At this pemp, the low clooland level light will flash
occasionally when I start the car but then go out.  the heater gets
warm but it is not as hot as I would expect, I have it turned into the
red and the air is just warm to the touch.

The second fault is the miles per gallon, I got 28mpg on the last tank,
which from what I have read is shockingly low for this type of car.  I
do, however, get a constant 'wiff' of diesel from the engine which
suggests to me that I have a leak somwhere.

I am now at a crossroads, I am reasonably proficient when it comes to
doing work on a car having worked on countless CVH issues with a
Scimitar I also own.  What are the likely causes?  I am more concerned
with the coolant level as I don't want an overheated engine, am I
looking at a head gasket problem, or is it more likely that the water
pump has failed?  I have already had to replace the power steering pump
on the car as this failed within a week of buying the car.

The car had been unused for a couple of years prior to me buying it and
the previous owner put it through an MOT which it passed without any
warnings.

Is it work me doing this work or just getting rid?