Gas vs PSD
Hotshot
Joined: May 2005
Posts: 13,484
Likes: 42
From: Stevens Point, WI
Besides pretty much all imports. I remember my 300I6 in my 89 F250 had those stupid taper plugs. Every oil change it was routine to go and tighten the plugs because they were all loose. When it came time to change them they were either finger loose and no socket was needed or they were seized in. I hate tapered plug seats! I don't have a single engine around with tapered plugs and I have yet (and I do ALLOT of vehicle/motor work) to come across a crush washer plug seized in a head. The only plugs I ever had problems with are the taper seat ones and it was the only motor around with them. I had to drill a plug out of a dodge caravan aluminum head once, that was a taper plug. Broke a plugs thread off in a head once trying to take it out, that was a taper fit head, in fact the 300I6 I mentioned earlier. But snowmobiles, lawn mowers, weed eaters, water pumps, power washers, all my cars, wifes mini van, leaf blowers, chain saws, I could go on and on all use crush washers and never ever once had a problem with any of them my entire life.
Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
My old all iron 74' 302 has tapered seat plugs also. Never had an issue. Maybe I'm just lucky or actually no what I'm doing. I never seemed to have good luck so I'll go with the later.
You can go on Rock Auto's website and search through different vehicles. Their database is usually pretty accurrate and gives you a good picture of the plug so you can see what the vehicles engine specs washer vs taper.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,562
Likes: 423
From: Long Island USA
I should elaborate, I haven't worked anything "modern" but Ford and Chevy stuff. And my Chevy experience is limited. Everything I've seen with crush washers is old... But that's MY experience. Not anyone else's 
Lead Driver
Joined: Jan 2006
Posts: 6,267
Likes: 5
What actually wears out in a spark plug?
Why can't you take them out, give them an acid bath, and put them back in?
an old 5.0 chev motor in a pickup i had took the threads out with the sparkplug.
Why can't you take them out, give them an acid bath, and put them back in?
an old 5.0 chev motor in a pickup i had took the threads out with the sparkplug.
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Cargo Master
Joined: Jan 2005
Posts: 2,413
Likes: 11
Actually, if you follow the maintenance schedule, leaving the stock plugs in there for 100K miles, you WILL most likely have a plug ejected. Either before the change because of corrosion, or after, because you took threads out of the aluminum head that were basically welded to the plug.
But the key thing is "torque wrench". And, using some anti-seize (which is also not in the directions, although USED to be on the Motorcraft website, can't find it anymore).
The threads in the head seem to be a pretty rough cut. Getting the plug in their correctly involves at least some sort of lubrication so you can actually get the plug wedged into the taper good enough to keep it there.
On top of that are mechanics who think they can do it by "feel" and are probably not getting even close to the proper torque.
Someone needs their sarcasm meter recalibrated
But the key thing is "torque wrench". And, using some anti-seize (which is also not in the directions, although USED to be on the Motorcraft website, can't find it anymore).
The threads in the head seem to be a pretty rough cut. Getting the plug in their correctly involves at least some sort of lubrication so you can actually get the plug wedged into the taper good enough to keep it there.
On top of that are mechanics who think they can do it by "feel" and are probably not getting even close to the proper torque.
Someone needs their sarcasm meter recalibrated
Every gas engine I own that a ford that has the 3v heads I pull the plugs between every 15k-20k. I got into the siezed plug very early in 05 or 06. I think the plug problems on these late model heads is plain stupid.
Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
Electrode wear, non functioning plug and etc. I actually pulled a double plat plug out of a 4.0l where the spark bypassed the platinum disc and arced away at the bare steel on the ground wire. Have had platinum discs fall off of plugs too. Have had plugs that looked brand new but would cause a misfire, poor running or would not fire at all. Stuff happens, plugs are fairly cheap and take a lot of abuse.
Postmaster
Joined: Apr 2006
Posts: 3,524
Likes: 2
From: CA Bay Area
The electrodes have enough material for few million miles especially platinum ones. . From what I know it is insulator that is loosing its values and current leaks outside -leading to weaker spark.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,562
Likes: 423
From: Long Island USA
It all depends on the plug, but there's usually not enough electrode left after 60K miles to regap and not effect where the spark sits in relation to the rest of the cylinder. Or bend the side electrode enough to fatigue it.
Better (and easier) to buy new and replace.
Better (and easier) to buy new and replace.
Logistics Pro
Joined: May 2011
Posts: 4,832
Likes: 668
From: Maine
