Freeing seized spark plugs-hot or cold engine?

[vanordinaire]

2006 Fiesta 1.25 'duratec' engine, alloy head.
I tried to remove the plugs at the weekend but bent a cheap plug socket on the first one without moving it. I stopped and am ready to soak in wd40 overnight and try again with a decent plug socket and a heavy bar.
Question is , should I warm up the engine first or do it cold?

[S0 What]

It's a zetec SE (sigma) not a duratec, thats just what the engine cover says
get the engine hot then spay on something decent not a water displacing spray yes WD is ok as a lube but there way better out there.
Plusgas is better or i use ATF thinned with acetone, but you have to use it in a metal oil can
I would do this a few times as the engine and plug cool the lube will be sucked down the thread (hopefully) if it's really tight i would do this for a few days (or till it works) in the hope it will work rather than snapping a plug in the head or stripping the thread, my usuall rule of thumb is if i cant undo it with a normal 1/2 ratchet then it's tight! i have used a breaker bar but me arse was squeeking when the plug finaly gave in and undid

[andyiley]

Agree with the above but have additional advice.

DON'T USE CHEAP TOOLS!

Cheap tools only cost more in knuckles & bolts than they do in tool costs.

[vanordinaire]

Thanks for the advice, still not sure if I should do it with the engine hot or cold though? If it's hot , does the alloy expand and tighten round the plug or does the hole expand and slacken the plug? Also does being hot weaken the alloy and make it more likely to damage it if forced?

[Sardonicus]

Hot always worked for me when no.3 was seized on 80's Honda's back in the day I prefer to use hot IMO also be careful here if it is fitted with Motorcraft plugs they are not strong bodied unlike NGK and can shear especially if there is any corrosion at the base, and would also agree with good quality tools and keep the ratchet/T bar etc extension straight/square when giving it some purchase

[S0 What]

Hot, the idea being that the differant metals expand at differant rates and the head "should" expand more than the plug, it's these differing expansions that cause the thread to seize in the first place when the fiction roughens the 2 surfaces, instead of a nice smooth thread you now have rough surfaces that grip each other.

[andyiley]

Another vote for hot, sorry, I missed that in your original question.

[mattyc69]

Engine nice and hot, fill the spark plug holes with plus gas and leave it to soak in,

Give it 24hrs get the car hot again bit more plus gas and give it a go with some quality tools at hand.

Never failed for me using this method.

[CarsOrBikes]

When is starts to move, you can do it up again, and re-release, it works the lube down the thread.