So is it 11 Nm or 15 Nm?
There is conflicting advice from Land Rover, but the likelihood is that 11 Nm is the correct tension on the 300Tdi timing belt. However, there are many websites, forums and videos that still regurgitate the 15 Nm torque specification when it is likely to be incorrect. If you're looking for parts, then see the 300Tdi timing belt parts diagram.
Why are there two tension values anyway?
Timing belts were snapping, or wearly prematurely, in the mid-90s and Land Rover issed replacement kits (STC4095K, STC4096K) and instructions for specific VIN ranges. The belt was found to be misaligned on the pulleys and would ride forward and rub on the timing case. The new parts consisted of pulleys with or without flanges and also altered their position longitudinally.
At the same time, the 300Tdi timing belt tension was reduced to 11 Nm as it was pulling on the fuel injection pump and bending the aluminium timing case. The injection pump bracket was also upgraded to add some structural rigidity to the injection pump. This this video compares the old and new brackets.
Tension or torque?
Technically we're talking about tension, where a sustained force of 11 Nm should be applied to the timing belt with a dial-type or bar-type torque indicating wrench. The clicker type torque wrenches cannot tell you what the torque is after the click occurs.
Let's look at the evidence
The 300Tdi workshop manual states 15 Nm for it's first, second and third editions - the latter being published in May 1999:
The 300Tdi overhaul manual also states 15 Nm for a new belt:
Yet the Technical Service Bulletin (TSB) L8424bu 0008 issued on 25th March 1998 states 11 Nm, and that it supersedes the tensions values in the workshop manual:
The conflict occurs because the 3rd edition Workshop Manual was printed after the TSB, but has the supposedly older tension figure. This is likely to be a printing error, or the manual wasn't updated following the TSB, as can happen in large organisations like Land Rover. The fact that the TSB states it supersedes the Workshop Manuals means it is more likely to be correct. Also, it has been found that the 300Tdi timing cover can be distorted by the timing belt tension being set too high. Therefore it would be better to err on the side of the lower value.