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Discussion Starter #1
Does anyone know why Ford recommends changing plugs in a warm as opposed to a cold Coyote engine? I have always changed plugs with a cold engine, especially one with aluminum heads, because the clearances are looser and aluminum has more tensile strength when cold.
 

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Se where you are coming from and would have thought better with a cold engine but ours is not to question why . Would be nice to find out Fords thinking on this . I do remember on earlier aluminum engines we had bad chemical reaction to plugs , steel bolts on heads , water pump etc seizing up badly . But would guess that should have been resolved nowadays . In the good old days I never gave it a thought when changing plugs unless they were in an awkward position and I could get burnt in doing so .

Our climate doesn't help but a month back I spent an hour under my daughters car in removing an alloy wheel seized on to the steel hub flange with a heavy hammer and a large length of wood . Very common due to the reaction of both metals and usually prevented by cleaning and applying Copper grease .
 

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Discussion Starter #3
I usually don't try to out engineer the engineers, but I get stuck with old habits and I think they are just testing us on this one.
And yes, galvanic reaction. You see it in the extreme around salt water when the engine falls out of your boat! It's also a good reason to use anti-seize compound where dissimilar metals meet such as spark plugs in aluminum heads and, as I just learned, where alloy wheels meet steel hubs.
 

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I’ve changed many spark plugs in about every ford engine produced since the 70s. All temperatures. Never really noticed a difference to be honest. In the real world we don’t always have a choice when the customer comes to the shop and is waiting. Not sure why they recommend warm but can say in the end I don’t personally think it matters much.
 

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Discussion Starter #5
I think you guys are right. I'll just keep on doing what I've been doin'. At least Coyote plug changes are a breeze. I once owned an 427 FE powered '68 Fastback. I wish I still had it, but NOT when it came time to change plugs.
 
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