Plugs are steel… heads are aluminum.
Not sure where that notion comes from.
The H.E., yes. The pre-H.E. uses washer seal plugs.
You do realise Paul that you can use the plug leads to remove the spark plugs once they have unthreaded? Just shove it back in the hole and push onto the plug and withdraw. Viola they are out!
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Less weight, less weight, better heat transfer, less weight, quicker to warm up and they’re not as heavy.
Downsides: louder - needs more material. The previous Jaguar engine would have been aluminium too but they didn’t get the noise under control and it was a new process back then. Aluminium is cutting edge if you want. The 5.3 is not much heavier than the 4.2- but twice the pistons, valves and heads!
Aluminum blocks are superior to iron. Only other downsides, you have to be careful with threads and of course cooling (head gasket).
Dang … good idea … Thanks for suggesting it, Robbin … 
btw, speaking of the wires, I did notice when I removed the wires from the terminals of the plugs I was surprised to find that one of the plug tips was covered with that same whitish build-up we see on battery terminals after awhile. 
No idea why it was like that on just a single plug. I also thought the last time I installed plugs (which is also when I put on the new cap, rotor and wires) I did put a dab of that dielectric grease that came with the wires on the tip of the plugs after installing them. If so, I REALLY don’t understand where that substance came from, esp. in only 5K miles. 
I had that on one of the plugs on my 2.9 it would cause the engine to feel like it was firing on 5 1/2 cylinders until it warmed up. Like you it was only the one plug. Never worked out why.
I would guess that the wire was never fully seated on the plug? So there was a tiny gap or just bad connection. The current was still able to get across and fire the plug. But you could get a weaker spark.
I find it very easy on the V12 not to fully seat the wire boots on the plug, as it’s very difficult to get a hand in there. I’ll sometimes need to use pliers, and I’ll make sure it’s super quiet so I can hear the “click”.
This is not a test I advise, but I’ve done it. While the engine is idling, grab a solid ground on the car with one hand, and then grab each wire boot on the distributor one by one with the other hand. Then do the same for each boot on the plugs. If you get a shock, then you don’t have a good connection/ground for that wire.
The shock only goes up to the wrist, but it sure hurts 
I would never advise anyone to get shocked… Health conditions… Is that masochistic or sadistic behavior…
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Idiot behavior? That’s why I did not advise. I did find a bad ground on one of my spark plugs via this test, and a bad plug wire another time. So it does work. I’m sure there are smarter approaches.
Getting a shock, when touching the spark plug boot, either at the distributor, or at the spark plug, generally is a sign that there is a hole, or a split, in the boot material insulation, so the volts jump through that path to the nearest least resistance ground path - in this case your body part as opposed to just using the path through the spark plug - thereby getting that big “OUCH” factor.
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Hi,
I got a Gunson product that cost me €9,95 Euros, it shows with a led light every pulse, you just place it on an ignition wire.
Easy and perhaps not necessary on a four or a six, but on the twelve if you have one plug missing, that little tool makes it easier to debug. No affiations, YMMV etc.
Cheers!
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Hello Pekka - would you be able to post a link of that Gunson item, with the led light indicator of the spark plug ignition - thanks, Tex.
Hi Tex,
Sure. Surprisingly I bought it ”old school” from a tool shop a few years ago, and not on-line, and I can see now that prices have gone up a bit, but it’s like this, a pen so to speak.
Cheers!
Pekka - thank you - I have been interested in finding something like this - Tex.
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There are spark testers on ebay… About ten bucks or less… Old school diagnosis
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Well, not being that much of a masochist, I was thinking about getting one of those plug “tester” gizmos that picks up current going through the wire inductively and lights up a light whenever it is. 
Yes, that’s the gizmo I was thinking of. I had one like it many years ago when I had my Opel GTs.
Make sure you have a pair of these for removal and install for those herd to get at spark plug boots.
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I was just fiddling with my 2002 Mazda 4-banger the other day. Wasted spark ignition, hence 2 coils. One wire from each coil goes to a spark plug and snaps onto the plug as one would expect. However, each coil is bolted down on top of a spark plug and connects to it directly, no HT lead at all. For these two plugs there is no snap, as the connector is a spring that just presses down on the top of the plug.
As a result of this setup, the openings in the cam cover for the four spark plugs are of two different configurations; the two that connect with a HT lead and seal with a boot are configured a bit differently than the two that get a coil bolted on top and seal with an O-ring.
Six feet away is my 2004 Honda Civic 4-banger with a completely different setup, coil-on-plug.