How to Free a Rusted or Seized Bolt Before the Weather Turns

What does a seized bolt mean?

A seized bolt is a fastener that will not turn because corrosion has locked its threads to the part around them. Rust and oxide build up in the gap between the threads and take up more room than the bare metal did, so the bolt is physically wedged in place.

Why bolts seize in the first place

A seized fastener is usually corrosion. Overtightening gets the blame, but it is rarely the culprit. Moisture gets between the threads and oxide forms, and that oxide takes up more room than the metal it came from. The threads are now packed with something that was not there when the bolt went in. On top of that, steel hardware in an aluminum casting sets up galvanic corrosion, which is why exhaust studs and cylinder head bolts are so reliably the ones that fight you. 

 

Do this before you put a wrench on it

• Give the penetrant time and a path in. Wire-brush the exposed threads first, because oil cannot travel through packed rust and road grime. 
• Clean the exposed threads and the shoulder of the nut. 
• Apply the penetrating oil and leave it, ideally for longer than feels necessary. Waiting, as the bard Tom Petty sang, is the hardest part. It's also the part that does the work. 
• Reapply before you reach for a longer bar.
• Shock it: short sharp taps to the bolt with a hammer break the oxide bond and open a path for the oil.
• Tighten slightly before loosening, if the fastener will take it.

 

Which penetrating oil, and why the difference matters

Two different problems, two different sprays. Thunderbolt foams on, to stay on, which is what you want on anything vertical or upside-down where a thin oil runs off before it has penetrated. Its formula is drawn beyond heavy rust and corrosion to free seized an stubborn parts, and it protects and lubricates the metal afterwards.

Laser is the pinpoint version. Its spray head puts a concentrated blend exactly where you aim it, and its climbing action penetrates the tightest areas, then leaves behind a protective film that lubricates and helps prevent future rust. Laser is also effective at displacing moisture on motors and equipment, which makes it useful well beyond a stuck bolt.

If you are working on something overhead or on a long vertical stub, take the foam. If you are trying to get oil into one specific joint without coating everything around it, take the pinpoint.

 

Heat and safety

Heat expands the outer part faster than the inner and cracks the corrosion bond. It is genuinely effective, and it is also how people set fires. Never take a torch near a fuel line, a fuel tank, a brake line or anything you have just soaked in a flammable penetrant. If the area has been sprayed, let it flash off first. 

 

Know when to take a breather

Forcing bolts is how they snap, and drilling out a snapped bolt and re-tapping the hole will eat the rest of your afternoon. A fastener that you extract slowly is cheaper than a casting you repair.

 

Stop the next one before it starts

The best cure for a seized bolt is an ounce of prevention: anti-seize on the threads during assembly. Excel+ Heavy-Duty Anti-Seize is a copper-moly blend that contains rust and corrosion inhibitors, giving your connectors a good long life. It seals out moisture, gases and corrosive fluids from threaded connections, preventing seizing, galling and premature wear, even under high temperatures and extreme pressures.

(That last part is what earns it a place in a Buffalo shop. Anything under a vehicle here spends six months in salt spray and freeze-thaw, which is precisely the condition that welds hardware into place.)

 

Frequently asked questions

Is a seized bolt the same as a stripped bolt?

No. A stripped bolt spins without biting because its threads are gone. A seized bolt will not turn at all because corrosion has bonded the threads together. The fixes are different. A stripped bolt needs a new fastener or a re-tapped hole. A seized one needs penetrating oil, patience and sometimes heat.

Why do bolts seize in the first place?

Moisture gets between the threads and forms oxide, which takes up more room than the metal it replaced. Steel hardware in an aluminum casting adds galvanic corrosion on top of that, which is why exhaust studs and cylinder head bolts seize so often.

How long should penetrating oil sit on a seized bolt?

Longer than feels necessary. Wire-brush the exposed threads first so the oil has a path in. Apply it and leave it alone. Reapply before you reach for a longer bar. A few sharp taps with a hammer break the oxide bond and open a path for the oil.

Can you free a seized bolt without heat?

Often, yes. Penetrating oil, time, tapping and a slight tighten-then-loosen will free most of them. Heat is the last resort, and it never goes near a fuel line, a fuel tank, a brake line or anything you have just soaked in a flammable penetrant.

How do you stop bolts from seizing?

Anti-seize on the threads during assembly. Excel+ Heavy-Duty Anti-Seize seals out moisture, gases and corrosive fluids from threaded connections, so the fastener backs out again next season instead of snapping.

If you are stocking a bay for the season, check out our Which Grease? guide to see which lubricant handles which job best. Shops and fleets buying Thunderbolt, Laser or Excel+ by the case should ask about volume pricing. Everything ships from Buffalo, New York.