Implications of a blown plug

[Opsimath]

My 2003 Expy blew a plug a couple of weeks ago stranding my wife on the side of the road. Our mechanic fixed it, no problem, but told my wife once one plug blows on this engine odds are good others will go. Now she won't drive the car.

I'm failing to see how blowing one plug could make it more likely others will blow. Am I missing something? Logic and my personal cred as a mechanic will never overcome what the expert told her so sadly the car will be sold but I want to be sure I understand the implications of a blown plug on this engine so I can sell it in good faith.

 

[ChrisOIFdoc]

The mechanic is only assuming more will blow based on the history of these particular heads. One plug blowing does not imply the other 7 will blow anytime soon. It only implies of the possibility. I've heli-coiled 2 so far in 4 years.

 

[BRIANGEE]

Is one blown plug really enough to cripple an 8 cylinder vehicle? I would've thought it possible to make it home but with reduced power (after pulling the injector connector).

 

[Opsimath]

@BRIANGEE you certainly wouldn't think so. I only have my wife's account to go by and she swore it was barely able to pull away from the stoplight before she parked it, but she is not very mechanically minded so take it for what it's worth.

@ChrisOIFdoc thanks for confirming what I assumed to be true. I argued the car was no worse after the fix than it was before but she went straight out and leased a 2018 Forrester. <sigh>

 

[1955moose]

If and when all eight spark plugs are torqued correctly, which is no easy feat! Under torqued say 10lbs or less, and boom! Same thing if over torqued say 23 pounds or more, they strip out the little threads that are there. It's a slippery slope on first editions. If they would have only added 4-5 more threads, this would hands down been the most trouble free expedition.

Sent from my N9131 using Tapatalk

 

[JExpedition07]

That mechanic is assuming, unless he has a magic ball. Boy she did quite the downgrade on that deal.

 

[Bain64]

Re-torque the other 7 plugs, add 5 ft-lbs to spec, and it's good to go. Were the plugs changed within the last few months? I lost a single plug on a 2004 4.6L a few months after changing plugs myself... I then got to learn all about the short threads and torquing procedures for these motors... I still see that old Marquis driving around town, I could've saved a lot of wrench time keeping that car but dang I love to drive the Expedition so much more.

 

[johnboneske]

I have owned 2 5.4 expeditions with the same 2 valve engines... My current expedition is on its 2nd engine too. I have NEVER had a problem with them blowing plugs out of the cylinders. Have had other problems though. LOL

It wouldn't even cross my mind to that problem, it may on the V10 however... My first had 260k on it when I sold it, my current has 205k on it.