[BrendanP]

My partners 2011 diesel with 201,000 miles is now getting harder to start from cold. After the glow plug light goes out it takes a good 5-6 seconds of cranking to fire up, and then it runs rough for a few more seconds until settling down to a smooth idle. I suspect one or more glow-plugs have failed, but I'm reluctant to change them after reading about how they can snap-off or strip the thread from the cylinder head even if you can remove them.

For this reason, I'm tempted to leave them unless and until the cold starting becomes intolerable.

On my own 2015 diesel, I don't have these issues, but would it be good idea to remove the glow plugs and refit them, if this makes them less likely to get stuck as the car gets older? Is there any recommended compound that can be applied to the threads that will make them easier to remove the nest time?

[sundiz]

Oil, time, heat and tools. I used these tricks and did not have any issue removing them.

Glow Plug tips and tricks - YouTube

I think best thing would be using a reamer, but I was not able to find one. If you decide to put some sort of grease  for easier removal in the future, make sure it will work with aluminium cylinder head. One member put copper grease, which basicly welded the plugs to the head. Not even a machine shop was able to remove them...

[Ranga2966]

I have a 2014 and was having the same issues. Easy job to replace glow plugs. Mine undid quite easily. If concerned a squirt of wd40 and let it soak overnight. When I replaced with the new ones I used a bit of never seize on the thread of glow plug.