Changing BMW Diesel Glow Plugs – Complete Guide & Tips
Regardless of your BMW's age, its glow plugs will eventually fail. Like any diesel vehicle, your BMW has four glow plugs (six in six-cylinder models) that preheat the combustion chamber and make starting easier on cold mornings. BMW also uses a post-glow function that keeps the glow plugs running for a few minutes after starting – to reduce emissions.
Why You Should Replace Defective BMW Glow Plugs Immediately
Many BMW owners don't know this: In vehicles with a diesel particulate filter (DPF), a defective glow plug prevents the regeneration of the DPF system. This can lead to expensive repairs to the particulate filter.
If you are not sure whether a glow plug is defective – read out the fault codes with our BMW diagnostic software and delete them after replacement.
Always Replace All Glow Plugs at Once
A common mistake: only replacing the defective glow plug. This is not recommended – and here's why:
- Accessing the glow plugs requires removing several plastic covers – which takes a lot of time
- All glow plugs have been in operation for the same amount of time – the remaining ones will soon fail as well
- Another replacement means a lot of effort again
Recommendation: Always replace the entire set when changing glow plugs. For BMW diesels, we recommend BERU brand glow plugs – high quality and durable.
Stuck BMW Glow Plugs – How to Avoid Problems
One of the biggest challenges when changing glow plugs on a BMW diesel is the risk of the plugs seizing in the cylinder head. If they break off, either the cylinder head must be removed or a specialist must remove the plug on site – both expensive and time-consuming.
Causes of stuck glow plugs:
- Carbon deposits between the glow plug body and the cylinder head
- Corrosion on the thread
Best method – soak glow plugs overnight:
Always assume the glow plugs are stuck. The best method is to soak them overnight with a good penetrating oil:
- Kano Kroil – penetrates deep into the thread, dissolves carbon and corrosion (first recommendation)
- 50/50 mixture of ATF oil and acetone – very effective alternative
- 50/50 mixture of cola and vinegar – simple home remedy alternative
Step-by-step removal:
- Soak glow plugs in penetrating oil overnight
- First tighten the plug slightly to loosen corrosion deposits on the thread
- Then loosen slowly with even pressure
- Gently rock the plug back and forth – never use force
- If resistance is met: stop the process and soak again
- When unscrewing, spray Brunox Turbo Spray into the thread – with each turn
Important: Do not use WD-40 – it is not suitable for loosening stuck glow plugs!
Recommended Penetrating Fluids for BMW Glow Plugs
- ✓ Kano Kroil – best choice
- ✓ Brunox Turbo Spray
- ✓ PlusGas Spray
- ✓ Liquid Wrench Penetrating Spray
- ✓ BG In-Force Penetrating Spray
- ✓ 50/50 ATF oil and acetone
- ✓ 50/50 cola and vinegar
- ✗ WD-40 – not suitable!
Installing New Glow Plugs – How to Prevent Future Problems
When installing new glow plugs, make sure to lubricate the thread with high-temperature ceramic grease. This prevents them from seizing in the cylinder head later. Conventional copper grease is not suitable for this purpose.
After Glow Plug Replacement – Clear Fault Codes
After replacing the BMW glow plugs, the fault codes must be cleared with BMW diagnostic software to ensure proper operation. Use our BMW ISTA or INPA software for this – available for download immediately after purchase.