This is owner experience, from the threads about the engine mount bolts. The cases are off side mount bolts, but the sockets, leverage and penetrating oil advice is what owners used on stubborn bolts generally. Nobody tested one method against another. Use a method that suits the part: grinding, drilling and welding near fuel, plastic, wiring and hoses carry real risk.
Engine mount bolts
This is the biggest source of trouble in the thread. Old bolts are often rusted along the whole thread.
- Use 6-point (flat drive) sockets. Ordinary serrated sockets rounded a stubborn bolt, and a 6-point socket and an 18" breaker bar shifted it with a crack. These grip on the flats rather than the corners. 6-point ring spanners exist too.
- Over-tightened bracket bolts. One car's three bracket bolts had been done up so hard that one started to round and another did round off. The fix was welding a large washer with a 14 mm hole to the nut, building up weld on top, then welding a large nut on top of that, so lots more torque could be applied. That is not a job for a plastic car on the driveway, so it was done at a workshop. Heat from a blowtorch is also an option in some places, but not in confined spaces or near plastic.
- Off side horror stories (2010 to 2011). One owner's three bracket bolts were seized solid. He snapped three extension pieces on the bolt that goes up through the channel, cut the lower part of the mount out with a hand grinder, and it took him two days. His view: the passenger side is half an hour and the off side needs a grinder on the tool list. Two others gave up after hours of levering and took their cars to a garage, and another rounded the top nut (despite the 45 Nm torque) and ground it off. One drilled at a bolt with two new HSS bits without getting it out. On the other hand two owners found the bolts came off easily, so it depends on the car.
- Penetrating oil. One owner suggests soaking the bolts holding the top of the mount to the engine with WD-40 for 24 hours or more. Another did that, twice, and they still wouldn't move. Others say WD-40 is poor for this and recommend a proper penetrating oil, naming Plusgas and Krost.
- Tools that helped. A small battery impact wrench on the off side, as it fits above the bracket. A 3/8 inch drive ratchet with a low-profile 15 mm socket on the NA off side, with the jack handle slipped over the ratchet handle as a long breaker bar. One owner spent 2.5 hours on one evening with the wrong sizes before finding a 1/2 to 3/8 inch adaptor at Machine Mart.
- Use the leverage you have. One owner got a smaller ratchet over the bolt and used a long bar over the ratchet handle to undo it from underneath.
One mount-specific problem, glue squeezed into the access hole, is in Engine mount replacement.
Seized fixings elsewhere in the guides
- Undertrays: removing and refitting has a section on seized and rounded bolts, including Allen heads.
- Wheel arches: liners, rusted fixings, tyre rubbing and extensions covers rusted-in liner screws, cutting the heads off and what owners refitted instead.
- Fuel filler surround: removing it and dealing with spinning bolts.
- Post-cat lambda sensor replacement has a step on getting the sensor unstuck.
Help wanted
We don't know which of these methods owners would pick again, or whether any of the bolts have a known torque or thread that makes them more likely to seize. If you have freed a seized bolt on another part of the car, please tell us which one and how.