Hi

Glow plugs should last quite a while, but you need to make sure the plugs you use are correct for both your engine and suited to the particular fuel you use.

Things like the ambient temperature play their part also - on both the tuning and what plug works best.

I'm in the UK, use 25 percent nitro fuel and find that RB No 6 plugs work well. Less nitro = hotter plug. More nitro = colder plug.

I inspect my plug after every run. If it starts to look dull, I change it BEFORE it breaks. How long they last depends on how hard/frequently you use your engine and also how lean you go with the mixtures. But you should find that they last between at least 2 weeks (2 race meetings) to 2 months (8 race meetings).