Penetrating oils are the best starting point for freeing glow plugs that have seized due to heat, carbon buildup, or corrosion in diesel engines. In practice, many technicians rely on Kano Kroil, with PB Blaster and Liquid Wrench as strong alternatives. Use these products sparingly and follow safety and maintenance guidelines to minimize the risk of damaging the glow plugs or cylinder head.
Why a penetrating oil is the tool of choice
Penetrating oils are formulated to creep into tight spaces and break down rust and carbon around the glow plug threads. They lubricate the interface and reduce friction, making it easier to turn the plug without snapping the ceramic or metallic components. This approach is particularly effective when plugs are stubborn from long service, heat cycles, or prior work in the engine.
Top lubricants technicians reach for
Below are the most commonly recommended penetrating oils used to free glow plugs. Availability can vary by region, and users often have a preferred brand based on past personal results.
- Kroil Penetrating Oil (Kano Kroil)
- PB Blaster Penetrating Oil
- Liquid Wrench Penetrating Oil
- WD-40 Specialist Rust Release Penetrant
These products are designed to loosen corrosion and carbon from the plug threads and seating surfaces. Choice among them often comes down to regional availability and personal experience; Kroil is frequently favored for severe seizures, while PB Blaster and Liquid Wrench are popular, widely accessible options. Apply sparingly to the glow plug wells and allow time to soak, reapplying as needed without saturating electrical connections.
How to use penetrating oil to free glow plugs
Here are practical steps technicians typically follow. This is a general guide and should be adapted to your vehicle’s service manual.
- Ensure the engine and the glow plug system are cool. Disconnect the battery to prevent any electrical shorts.
- Gain access to the glow plug wells and clean the immediate area around the plugs to prevent dirt from entering the cylinder head.
- Carefully spray penetrating oil around the base of each glow plug, avoiding direct contact with the electrical connectors. Allow the oil to soak for 15–60 minutes; for especially stubborn plugs, reapply and extend the soak time.
- With the correct size glow plug socket, attempt to turn the plug counterclockwise with steady, even pressure. If the plug begins to rotate, continue to apply oil and gradual torque. Do not yank or use brute force.
- If there is no movement after multiple soaking cycles, consider applying a gentle heat source to surrounding metal areas (not directly to the plug) to expand the metal slightly, then reattempt. Avoid overheating to prevent damage to seals or surrounding components.
- Once the glow plug loosens, remove it carefully and inspect the threads. Clean the threads in the head and apply an appropriate anti-seize or thread lubricant if recommended by the vehicle manufacturer for reinstall. Reinstall with the correct torque specification and new seals if applicable.
In practice, patience is key. For severely corroded plugs, repeated soaking and incremental torque are safer than forcing the plug, which risks breaking the plug off in the cylinder head and causing costly damage.
Safety and reinstallation tips
Before you reinstall glow plugs, keep these considerations in mind to minimize future problems and ensure a reliable seal.
- Follow the vehicle maker’s torque specs for glow plugs and use a calibrated torque wrench. Torque values vary by engine, so consult the service manual.
- If the plug or surrounding threads show damage, replace the affected glow plug(s) and consider replacing any copper washers or seals as directed by the manufacturer.
- Use the manufacturer-approved lubricant or anti-seize compound on threads if recommended. Apply sparingly to prevent attracting dirt or interfering with electrical contacts.
- Inspect the glow plug harness and electrical connectors for corrosion or damage before reinstalling. Replace damaged connectors as needed.
When to call a professional
If a glow plug remains stubborn after extended soaking, or if you suspect the plug is already broken or damaged, professional service is advised. Extracting a broken glow plug fragment requires specialized tools and experience to avoid internal engine damage.
Summary
For removing seized glow plugs, penetrating oils are the best first-line solution. Kano Kroil is widely regarded as highly effective, with PB Blaster and Liquid Wrench as solid alternatives. Use these products sparingly, allow time to soak, and proceed with careful, incremental torque to reduce the risk of breaking the plug. Always follow the vehicle’s service manual for torque specs, thread treatment, and replacement parts, and seek professional help if a plug refuses to come free or breaks off.