Volkswagen CL Umwelt TD Estate.  1.9  AAZ engine   1998 S reg.

Emptied cooling system yesterday. Refilled using the recommended antifreeze.
Today after driving around 15 miles the car overheated, smoke from bonnet,
kind of burning smell. Shut off straight away and called the RAC, they
arrived after about 45 minutes by which time things had cooled down. He said
he wasn't sure but thinks it may be the water pump. He told us to drive home
(about half a mile) slowly and switch off at traffic lights etc. he followed
us, just as we got home the temp guage shot to 90 (no smoke this time but
faint smell)

The main thing I was wondering was could it be an air lock instead of the
water pump, top and bottom hoses seem at the correct temp (bottom one cooler
than top, but still pretty warm) the fans did kick in and off again after we
refilled at the coolent change, but I don't think it took in as much water
as it should. This being the first Volkswagen I have owned, previous cars
having had bleeders.

Any advice would be greatly appreciated,
thanks,
Mandie.