Can you drive with a broken head bolt?

In short: you should not drive a vehicle with a broken head bolt. A broken head bolt can compromise the cylinder head gasket, cooling and oil passages, and overall engine integrity, which can lead to severe and costly damage. If you suspect a broken head bolt, stop driving and arrange safe transport to a qualified mechanic.

What a head bolt does and what "broken" means

To understand why driving with a broken head bolt is risky, it helps to know the bolt’s role and how failures occur.

How head bolts function

• Head bolts clamp the cylinder head to the engine block, sealing the combustion chambers and aligning oil and coolant passages.


• Many modern engines use torque-to-yield bolts that stretch when torqued to spec, creating a precise clamping force; these are often single-use and replaced during head work.


• A properly torqued head bolt maintains the head gasket seal under high pressure and temperature, preventing leaks between the head and block.

When a bolt breaks or loses clamping force, the head gasket can no longer seal reliably, which can allow coolant and oil to mix or leak, and it can lead to warping or other head damage. In many engines, a broken bolt means the entire head may need inspection, and the repair is invasive and costly.

Common ways a head bolt can fail

• Shearing of the bolt where it threads into the block or head due to overload or impact.


• Stretching or loss of clamping force from overheating or over-torquing, reducing head gasket sealing.


• Corrosion or seized threads that prevent proper installation or removal.


• Thread damage in the block or head that prevents secure seating of the bolt.

Regardless of the cause, a broken head bolt typically signals compromised head gasket integrity and requires professional assessment to avoid further damage.

Signs a head bolt may be broken or failing

Recognizing possible failure early can help you decide how to proceed. The following symptoms can accompany head bolt issues, though they may overlap with other problems.

Indications to watch for

• Overheating or rapid temperature spikes, especially after a boiled cooling system episode.


• Loss of engine power, misfires, or rough running without an obvious external cause.


• Coolant loss with no visible leak, or coolant in the oil causing milky oil on the dipstick.


• Exhaust with unusual white smoke indicating coolant entering the combustion chamber.


• Oil leaks near the head or engine front that worsen over time.


• Diagnostic trouble codes related to compression, misfire, or cooling system issues.

Note that these symptoms can stem from other problems (gasket, coolant system, or timing issues). A professional diagnostic is essential to confirm a broken head bolt.

What to do if you suspect a broken head bolt

If you observe any of the signs above, take careful, safety-conscious steps to protect yourself and your vehicle.

Immediate steps

• Safely pull over and turn off the engine to prevent further damage.


• Do not continue driving, restart attempts, or run the engine aggressively.


• Call roadside assistance or arrange a tow to a qualified repair shop.


• Do not attempt DIY repair on the roadside; head work requires specialized tools, torque specs, and often a machine shop assessment.

Tow and professional inspection are typically far less costly than the potential engine damage that could occur from driving with a broken head bolt.

Repair options, costs, and timeline

Repair work for a broken head bolt usually involves more than just replacing the bolt. The engine and head must be inspected for warping and gasket integrity, and the head may need resurfacing or replacement.

Common repair steps

• Remove the cylinder head to inspect for warp, cracks, or gasket damage.


• Replace all head bolts (one-time-use bolts are common) with new, correctly torqued fasteners per the manufacturer’s specs.


• Replace the head gasket and any damaged seals; flush and refill the cooling system and engine oil.


• Inspect or machine the cylinder head and engine block deck as needed to restore proper flatness and seal integrity.


• Check timing components, coolant passages, and related systems that may have been affected.

Costs vary widely by vehicle and region. A head gasket replacement with bolt replacement and possible head machining can range from roughly mid-two- to mid-five-figure dollars for some vehicles, while smaller engines in less complex setups may be less expensive. Timelines typically span 1–3 days at a reputable shop, assuming no additional damaged components are found.

Prevention and maintenance tips

Preventing head bolt problems largely comes down to proper maintenance, listening for early warning signs, and avoiding engine overheating.

Best practices to reduce risk

• Maintain cooling system health: fix leaks, replace coolant on schedule, and address overheating promptly.


• Follow manufacturer torque specifications exactly when performing any head work or bolt replacements.


• Use high-quality head bolts appropriate for your engine and replace them when removing the head.


• Address head gasket symptoms early to prevent escalation to bolt failure.

Consistent maintenance and early attention to cooling and compression issues can help prevent bolt-related failures and protect engine life.

Summary

Driving with a broken head bolt is not advisable due to the risk of severe engine damage, including head gasket failure, coolant/oil cross-contamination, and potential head warp. If you suspect a broken head bolt, safely stop the vehicle and arrange professional diagnosis and repair. Expect a comprehensive head work procedure if damage is found, with costs and timelines that vary by engine type. Regular maintenance and careful attention to overheating and cooling system health are the best defenses against head bolt failures.

How long can I drive a car with a blown head gasket?

You should not drive a car with a blown head gasket, as it can lead to catastrophic engine damage and will require more expensive repairs. However, the actual time it can be driven depends on the severity of the leak, with some vehicles being drivable for short distances and others seizing up almost immediately. It is best to get the car fixed as soon as possible to avoid permanent engine damage, such as overheating, or the mixing of oil and coolant. 
Factors affecting how long you can drive

• Severity of the leak: A minor leak that only requires adding a little coolant every so often will allow you to drive longer than a major one. 
• Location of the leak: A leak from combustion to water will cause rapid overheating, while a leak between two cylinders might allow the car to continue running with lost power. 
• External conditions: Hot weather puts more stress on the engine, making it less safe to drive with a blown head gasket than in cold weather. 
• Maintenance: Regularly topping off the coolant and oil can prolong the time you can drive, but it is a temporary solution that doesn't fix the underlying problem. 

Risks of driving with a blown head gasket

• Overheating: The engine can overheat quickly due to coolant loss, potentially causing a cracked cylinder head. 
• Engine seizure: The engine can seize up completely, requiring a full engine replacement. 
• Contaminated fluids: Coolant can get into the oil, turning it into a milky substance, which compromises the engine's lubrication system. 
• Further damage: Driving with a blown head gasket can cause further damage to other components, such as the catalytic converter, which increases repair costs. 

This video explains how to diagnose a bad head gasket: 57sRepair GeekYouTube · Mar 29, 2023
What to do if you think your head gasket is blown

• Pull over immediately: If you notice signs of a blown head gasket, such as steam from the engine, white smoke from the exhaust, or a milky substance on the oil cap, pull over as soon as it's safe to do so. 
• Do not drive the car: Avoid driving the car any further than necessary to get to a safe location. 
• Get it towed: Have the vehicle towed to a mechanic for an inspection and repair. 
• Consider temporary fixes: A temporary fix, like a head gasket sealer, may be an option for a short-term solution, but it is not a permanent fix and should be used cautiously. 

What to do if a bolt head breaks off?

When a bolt head breaks off, you can use a screw extractor set, a welding method, or a chisel/center punch to remove the bolt. The best method depends on the bolt's position and how much of it is left. 
Method 1: Use a screw extractor set 
This method is best for bolts with the head broken off flush or just below the surface. 

1. Center punch: Mark the exact center of the broken bolt with a center punch and hammer. 
2. Drill a pilot hole: Select a drill bit that is smaller than the bolt and drill a pilot hole into the center of the bolt. Using a left-handed drill bit can sometimes remove the bolt on its own. 
3. Insert the extractor: Tap the appropriately sized extractor into the hole and use a wrench or tap handle to turn it counter-clockwise. The extractor's threads will bite into the bolt and unscrew it. 

This video demonstrates how to use a screw extractor to remove a broken bolt: 1mdonyboy73YouTube · Jan 11, 2024
Method 2: Weld a nut to the bolt 
This method is ideal for bolts that have a portion sticking out. 

1. Place a nut: Fit a nut of the correct size over the broken part of the bolt. 
2. Weld: Weld the nut to the broken bolt shank. This creates a new "head" for the bolt. 
3. Cool down: Allow the weld to cool completely. The heat from welding can help break the bolt free, and the new nut allows you to use a wrench. 
4. Unscrew: Use a wrench to unscrew the bolt. 

You can watch this video to see how to weld a nut to a broken bolt: 58ssixtyfivefordYouTube · Feb 3, 2021
Method 3: Use a chisel or center punch 
This is a more manual method that works best for bolts where there is some surface to work with. 

1. Apply penetrant: Soak the area with a penetrating oil and let it sit. 
2. Chisel the bolt: Place the tip of a small, sharp chisel at an angle on the edge of the broken bolt. Hit the chisel with a hammer to bite into the bolt and start rotating it counter-clockwise. 
3. Rotate and repeat: Continue to work your way around the bolt, gently rotating it with the chisel until you can grip it with pliers or mole grips to remove it completely. 

This video shows how to remove a broken bolt with a chisel: 57sUltimate HandymanYouTube · Aug 21, 2016

What happens if a head bolt breaks?

Signs of a Broken Head Bolt
Compression loss leading to misfires or poor engine performance. Visible bolt damage – a missing bolt head or uneven clamping pressure. Strange noises – knocking, hissing, or excessive ticking from the engine.

Can you drive with a snapped head bolt?

Definitely not. You'll blow your head gasket at least.