Im tempted to replace the glow plugs but I hear they snap off rather too easily

 

I was very worried about that - look at it this way, if one does snap, you dont necessarily have to do anything, just leave it unplugged.... unless its allowing the crank to breathe your fine.

I spent a week spraying mine after my daily run with WD40 through the inlet manifold slats, then when i got home one night, engine upto full temp...i removed the inlet and did the job, they came out surpiringly easy - thats on a 137k 2005 535D.

Having said that i only did two the first time around as they had sent me 4 of the wrong sort (teach me to check part numbers before i start the job!) - i did the remaining four on a slightly cooler engine after fannying about fitting the controller (awful job) - and those 4 were slightly harder to do and more nerve wracking.

 

is it recommended to do it on a hot engine then? i was always under the impression that cold was best as the head material was less likely to give up and strip threads

 

Its to do with expansion etc - I did a lot of reading as after i'd purchased the plugs - I had numerous people warning me. My research concluded that a hot engine was better and on the two occasions i extracted the plugs, i'd say that is undoubtably the case.

What gave me confidence was my mechanic neighbour said that he hadn't had any issues before with BMW glows, only on cheaper brands like Vauxhall etc...

TIP: Use a wobble bar too to take some of the strain whilst turning on the ratchet