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Spark plug removal

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davewr | 17:23 Tue 07th Jul 2009 | Motoring
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What is the correct way to remove spark plugs from an alloy cylinder head? With the engine cold or warm?
On the old cars I worked on years ago I always did them cold but I've been told now to run the car up to normal temperature and then let it cool for a while, something to do with the different rates of contraction as metals cool.
I be glad to hear from someone who has a lot of experience.

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ITS BASICALLY making use of the co-efficient of expansion of metals.
Due to the fact that spark plugs now take that much longer to be changed you reduce the chance of stripping the threads if the engine is warm.
HOWEVER IF the spark plugs were correctly tightened in the first place you need not worry about cold or warm engine.
I wait till the engine is cold before I remove the plugs. Once removed I clean and reset the gap and clean the threads with a small wire brush...Before replacing them I lightly smear the threads with an anti sieze compound for easy extraction in the future. If I am renewing the plugs I still use the said compound and screw them carefully into place. When screwing the plugs in it should be a smooth operation if any resistence is found it could be a crossed thread and it is better to retract the plug and try again. I hope this is some help to you.S.O.G.
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Thanks for the info.
The plugs were supposed to have all been changed by a main dealer about 20,000 miles ago after the centre of one blew out due to water leaking into the wells. It was a problem on Fiestas & Focuses apparently. I'll just give it a try and if they don't come out easily I'll take it to the dealer again.
Thanks again.

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