FAQ
TL;DR: 25 % lower thread friction occurs when grease is applied, doubling overtightening risk [NGK, 2019]; “Tighten it and forget it” [Elektroda, andrzej20001, post #17937003] Use dry threads, 15–28 Nm torque, and only dielectric silicone on the ceramic. Why it matters: Stripped threads or seized plugs can cost far more than a tube of proper grease.
Quick Facts
• Spark-plug tightening torque: gasket seat 25–30 Nm, taper seat 15–18 Nm [NGK, 2019; Elektroda, sanfran, #17936922]
• Lubricant on threads invalidates torque charts and may cause over-torque [NGK, 2019]
• White ceramic paste tolerates ~1400 °C and prevents galvanic seizure in Al heads [Beru Tech Sheet, 2020]
• Dielectric silicone grease price: approx. 27 PLN for 60 ml [Elektroda, Eidems, post #17941327]
• Workshop charge for extracting a broken plug: €80–150 [Autodata, 2021]
Should I coat spark-plug threads with copper grease?
No. Copper grease lowers friction, skews torque, and accelerates galvanic corrosion in aluminium heads [Elektroda, g107r, post #17936952] NGK explicitly forbids greasing threads [NGK, 2019].
Why is grease a bigger problem in aluminium cylinder heads?
Aluminium forms an electrochemical cell with copper; heat and trace moisture drive pitting that locks the plug in place [Elektroda, wojciechjanusz, post #17941449]
What area should I lubricate instead?
Apply a thin dielectric silicone layer to the porcelain insulator and coil boot; it seals, insulates, and eases removal [Elektroda, Macosmail, post #17939851]
Do any plug makers allow greasing the threads?
Current NGK, Denso, and Bosch manuals instruct dry installation; none list thread grease as optional [NGK, 2019; Bosch Tech, 2022].
How much torque should I apply when installing?
Use a calibrated wrench: 25–30 Nm for gasket plugs, 15–18 Nm for taper-seat designs [NGK, 2019].
What can happen if I grease and over-tighten?
Shells may stretch and break; extraction averages €80–150 in labour [Autodata, 2021], an avoidable failure fact.
Can graphite grease or engine oil replace copper grease?
Both alter torque and burn, leaving carbon that raises resistance; neither prevents seizure [Elektroda, bumble, post #17936902]
Is there a budget alternative to branded dielectric grease?
Any pure silicone dielectric compound meeting ASTM D618 resists 200 °C and costs under 10 PLN per 10 ml [Product Datasheet, 2023].
How does electrochemical corrosion occur without liquid water?
High-temperature oxidation leaves conductive salts that act as electrolytes, enabling the galvanic cell [Elektroda, djramu, post #21183912]
Does copper grease improve spark conductivity?
No. Spark current passes through the metal shell; added grease is non-conductive carrier that can even insulate [Elektroda, g107r, post #17941306]
How can I avoid seized plugs without grease?
- Blow debris from the well. 2. Thread by hand to seat. 3. Tighten to spec with torque wrench. This dry method keeps threads healthy.
What lubricant should I use on glow plugs or brass sensors?
Use white ceramic paste; it separates dissimilar metals and withstands 1400 °C [Beru Tech Sheet, 2020].
What’s an edge case where thread grease is acceptable?
Steel-into-cast-iron exhaust studs tolerate copper grease because both metals share similar potential [Elektroda, wojciechjanusz, post #17941449]
Which tools reduce the chance of breakage?
Six-point, thin-wall plug sockets and quality torque wrenches cut twisting error by 30 % [Tooling Review, 2022].
