Could be the thermostat stuck closed - not letting coolant get round the whole system and cool efficiently.
Could be head gasket - check for oil in the coolant is the usual giveaway.
Could be water pump failed, meaning water not pumping round the engine.
Hope that helps
club.306.com
the diesel tank capacity for a 2001 306 Hdi is approx £80 so around 55litres
any diesel oil will be fine
Timing on a diesel? your haveing a laugh?
A Peugeot 306 that has a noisy fan and overheating may need a fan replacement. One may also look into the coolant or thermostat to resolve the issue.
TNT
put in more coolant but its not running hot
try picking up a new fan relay + check fuse and module fan behind bumper
Four
I have a problem with my Peugeot 306 deasel pump its not idling
under the steering wheel
Phase 1 and 2 = 1.9 Turbo Diesel Phase 3 = 2.0 HDI Turbo Diesel