Sometimes—but not on every bolt. Use thread sealant only where the engine’s service procedure or the bolt-maker’s instructions call for it, commonly on bolts whose threaded holes open into a coolant passage. Other bolts may require oil, and one cylinder head can have both treatments. Check the instructions for the exact engine and fastener set before installation.
When do cylinder-head bolts need sealant?
A bolt needs sealant when its threaded hole communicates with a coolant passage and the application instructions specify sealing. Fel-Pro’s cylinder-head gasket installation instructions say bolts entering coolant passages require a pliable, non-hardening sealer on the threads; bolts that do not enter those passages require oil. Fel-Pro’s torque-to-yield guidance likewise distinguishes bolts passing through a water jacket, which need thread sealer to help prevent corrosion and leaks, from bolts that are lubricated as specified.
That is a general principle, not a substitute for the service procedure. Hole locations and required treatments vary by engine, and the engine maker’s instructions take precedence. Do not assume all bolts on one cylinder head are treated alike.
How to determine the right treatment for each bolt
- Find the exact procedure. Use the service information for the engine’s make, model, year and configuration, along with the instructions supplied with the replacement bolts. Follow its bolt-position diagram, tightening sequence and staged torque or angle steps.
- Identify which threaded holes enter coolant. Use the service information or the fastener maker’s inspection guidance. Do not infer that every bolt is a “wet” bolt simply because it is on the cylinder head.
- Apply only the specified treatment at each position. A procedure may call for sealant on coolant-exposed bolts and oil on others. If the bolts come with a pre-applied sealant and their instructions say to install them as supplied, do not add more sealant or oil.
- Keep threaded holes clean and free of excess liquid. Pay particular attention to blind holes, which do not pass through. Remove contamination and follow the manual’s cleaning and preparation requirements; do not leave pooled oil or sealer in the bottom.
- Tighten exactly as specified. Use the prescribed sequence, tightening stages and fastener-specific instructions. There is no universal cylinder-head torque value or tightening procedure.
Why one head may use both oil and sealant
Each bolt position has its own path and preparation requirement. For example, the 2008 Jeep Grand Cherokee 4.7L Flex Fuel right-cylinder-head procedure calls for clean engine oil on ten M10 bolts and Mopar thread sealant with PTFE on four M8 bolts. Those instructions illustrate a mixed-treatment application; they are not specifications for other Jeep engines or other vehicles.
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- Locks and seals threaded fittings
- Resists leakage, vibration loosening, moisture, hydraulic fluids and diesel fuels
- Lubricates threads for easy assembly and disassembly
- Parts may be repositioned up to 4 hours after application
- Suggested Applications: head bolts into through holes, oil PSI sending units and sensors, oil and coolant lines, fuel fittings, rear axle fill plug, brake and power steering fittings
What can go wrong with excess sealant or oil?
Liquid trapped in a blind threaded hole can create hydraulic lock as the bolt is tightened. Fel-Pro warns that excess oil in a blind hole can cause false torque readings; the Payen cylinder-head bolt guide warns hydraulic lock can reduce clamp load or crack the block. In other words, a torque wrench reading does not necessarily mean the joint has achieved the intended clamping force if liquid is trapped beneath the bolt.
Use the sealant type and amount specified for the application, and avoid substituting a hardening product for instructions that call for a pliable, non-hardening sealer. If you cannot establish which holes are coolant-exposed or what preparation the replacement fasteners require, stop and consult the engine-specific service procedure or fastener supplier before tightening.
Quick Recap
Best Value
- OEM-Approved Performance: LOCTITE automotive products are not only OEM-specified but also designed and tested by leading auto manufacturers. Trusted by professionals in engine building and repair worldwide (PN: 483629)
- Dependable Thread Sealing: Fast-curing formula withstands pressures up to 10,000 PSI, ensuring leak-proof, long-lasting seals in demanding conditions
- Versatile Alternative: Replaces traditional tapes, pipe dopes, and pre-coated parts, offering a superior solution for a variety of sealing needs
- Wide Application Range: Perfect for stainless steel fittings, head bolts in through holes, oil pressure sending units, sensors, oil and coolant lines, and more
- Specialized Formulation: Engineered specifically for metal and tapered pipe thread fittings, providing a reliable and durable solution for automotive professionals
Rank #4
- OEM-Approved Performance: LOCTITE automotive products are not only OEM-specified but also designed and tested by leading auto manufacturers. Trusted by professionals in engine building and repair worldwide (PN: 1158514)
- Dependable Sealing: Provides lubrication for fasteners during assembly, ensuring a smooth and effective installation
- Strong Resistance: Seals gaps between threads to prevent premature loosening, maintaining a secure fit over time
- Corrosion Prevention: Protects against corrosion, facilitating easier disassembly in the future and reducing maintenance issues
- Versatile Applications: Ideal for a variety of uses, including head bolts, water pump bolts, thermostat housings, intake manifold bolts, and temperature sensors
Rank #3
- Economical general-purpose fitting sealant
- Outperforms tapes and pipe dopes
- Seals and resists pressure in air, oil, diesel fuel and hydraulic systems
- Remains pliable at higher and lower temperatures
- Suggested Applications: Air conditioning fittings, temperature sending fittings, hydraulic fittings. Flash point: 23.3333
Rank #2
- Locks and seals threaded fittings
- Resists leakage, vibration loosening, moisture, hydraulic fluids and diesel fuels
- Lubricates threads for easy assembly and disassembly
- Parts may be repositioned up to 4 hours after application
- Suggested Applications: head bolts into through holes, oil PSI sending units and sensors, oil and coolant lines, fuel fittings, rear axle fill plug, brake and power steering fittings
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