It is definitely something you can do yourself, though might take awhile on the first attempt. The second time is a lot easier, as I found out having purchased the cheapest set available only to have them go a few months later. So consder getting Bosch, or at least an alternative branded name.
If you are considering doing other things to the car invest in the engine service manual (40 notes from Volvo). If not use the online one at
www.k-jet.org
If you do a search for "glow plugs 5 and 6" on the forums you will get a couple of threads explaining how to do it. A set of ratcheted spanners (40 notes, from China presumably, obtainable from Halfords) is useful and some open ended spanners (8mm for the nuts and I think 12mm for the plugs themselves). Illumination is essential, an engine lamp or equivalent.
The 6 glow plugs fit into the cylinder head just below their respective injectors on the driver's side of the engine. The electical supply comes from the battery via a relay which goes to plug one (at the front of the engine) then via a copper strip to nos 2 and 3. Another strip runs from plugs 4 to 6 and the 2 are joined by a connecting wire running between plugs 3 and 4 thus providing current to all plugs.
Remove the nuts holding on the strips/wire to the plugs. Take off the plastic shield which covers the pump belt (at the back of the engine) as no 6 is best approached from behind. The engine will start with 5 new plugs and you can if you wish wait for warmer weather to do the trickiest one, no 5. You will find a pillow is required for 4 (5) 6, the reason being that it is difficult to manoever your fingers between the injector lines and attempt to manipulate a spanner and see what you are doing without being able to look down over the engine - so you have to lie across the front of the bay, not a comfortable position without some padding.
Plug no 6 is close to the back so your fingers have some free space, but 5 is buried behind the pump bracket and the lines block free movement of your fingers, so even if you get a spanner on you will find that only a few degrees of movement result from your efforts. Ratcheted spanners are useful because only a few degrees are necessary to remove a nut. I ended up chopping some spanners in half. I don't think this is a task that any two people do in exactly the same fashion.
Be careful when replacing plugs and nuts on 5 and 6, use copper grease and make sure the plugs are turning easily. The last thing you want to do is damage a thread...
john
john