Can a spark plug loosen, blow out and require head replacement?

My 2003 Ford Ranger engine(33,000 miles); bought used 22,000 miles) began to make a loud whirlling sound. Tow truck driver pulled out a totally disconnected spark plug. The truck seemed to run well after replacing the spark plug. At garage, mechanic said all spark plugs were off brand (not Mororcraft); the head ruined and must be replaced. Cross threaded and oil on cylinder…how can truck be driven for 11,000 miles and blow spark plug? New head necessary? Comments appreciated…

Blow out a plug? Sure, this does happen. Happened to me with my wife’s Mazda Protege. Need a new cylinder head? Most likely not. The only reason to consider a new or replacement head is if there are cracks between the spark plug hole and one of the valves. Most machine shops would put a heli-coil into the spark plug hole to restore the threads. It is best to remove the cylinder head to do this, but not absolutely necessary if you have a skilled machinist do it. I would try the heli-coil first before laying out big bucks for a replacement head IMHO.

With the wife’s car, I replaced the plug, torqued it down to the proper torque, and never had a problem with it for the next 30,000 miles before we sold it. That includes replacing that same plug twice since.

I would start by getting a second opinion.  Not that what the mechanic must be wrong, but well it sounds a little fishy.  

That second opinion will require someone with hands on the car. While I do recommend using the same brand plug that came with the car, I have never heard of a situation like your due to plugs. One maybe all of them no.

Most of the time when a plug blows out it can be fixed cheaply.  

Since the truck only has 33,000 miles and plugs were replaced at least once, it just does not wash.

Not sure what he was getting at regarding the brand of spark plug except to point out that someone must have replaced the originals.

Is he saying ALL the spark plugs were cross threaded? That still doesn’t justify replacing the head, though. A set of HeliCoils wouldfix that problem.
Oil on (in?) cylinder? Again, that also doesn’t necessarily point to replacing the head.

Perhaps it’s the mechanic that needs to be replaced. Or at least get some clarification as to what he’s saying, preferably in writing.

There is definiitely an issue of plugs blowing out of the 5.3L Ford Triton V-8 engine, taking the threads WITH the plug. That appears to be a faulty design, although it usually happens AFTER the warranty expires so Ford is absolved of blame. I’ve not heard of that happening on a 4 cyl Ranger, so I’m guessing it just worked loose and blew out. Did the plug appear to have the head’s threads still with it? In that case, it may need a helicoil repair. If the shop you took it to is not capable of doing that sort of repair, find another shop. Stuff happens, even to the best of them. Shoot, I had a helicoil repair done on a Mercedes 190SL nearly 40 years ago. It’s a proven method.

This happened because someone didn’t properly torque the plugs when they installed them. It took this long for the first one to work its way out.

A good shop can put in a thread insert without removing the cylinder head – they have to vacuum out the metal chips afterwards, and hopefully they have a bore scope so they can look and make sure all the chips are gone. It can be done, but you don’t want Skippy the Intern practicing on your car. Find an independent shop with some racing experience, and look for the grizzled veteran mechanic.

There are much, much better thread repair inserts than Helicoils, too. Find out what exactly they’re going to use (some people use the word “helicoil” for any thread insert), and insist on something better than a glorified spring.

Spark plug blowouts are normally caused by someone overtightening the plugs.
Another cause (not in this case) would be when someone allows plugs to remain in place for a long time. The plugs may gald to the threads in the cylinder head and when the plugs are finally removed they may bring some of the threads with them. This leaves weakened threads and a plug can blow out at any time; same as with overtightening them.

There are a number of methods available (Heli-Coil, Thread-Sert, etc.)for thread repair and you should not have to replace the cylinder head.
Spark plug thread repair is a common procedure.

I’m facing this very same issue in my 2002 Escape right now. One thing that makes me mad about it is that the torque spec on the plugs is just 11 ft lbs. I think I ended up putting them on with 15, but it still wasn’t enough. Now the engine has what appears to be a loud tappet noise. I took it apart today, hoping to find a bad lash adjuster or rocker, but both appear to be fine. Then, when I tried to take out the plug, it did not feel right. I fear the garage did something wrong.

I think I’m out a head at this point, so yes, I’m afraid it can happen. In my case, it’s about 13 hours of labor to replace the head on the V6. I looked into doing that myself, and then quickly changed my mind. So, $500 for a new head, and 13 hours of labor, new head gaskets, new head bolts.

I don’t understand an 11 ft lb spec for spark plugs. It has about 7 threads holding the plug in. You’d think it could stand 30 ft lbs.

Good luck with yours. It’s back to the drawing board with mine.

I just checked the Haynes repair manual for my '02 Tahoe 5.3L V8.

The torque specs for the OEM plugs are 132 ins-lb.

I googled up a torque ‘converter’ (conversion calculator) and found 132ins-lb = 11 ft lbs.

I imagine some plugs/heads require different torque specs.

The OEM plugs in my '00 Silhouette 3.4L V6 require 20 ft lbs.

I’m not sure I understand. The spec is 11 and you went to 15 but felt it wasn’t enough? What makes you say that? Over-torquing stretches threads. This is the most common reason for their failure, especially since aluminum heads became more mainstream. FWIW, I have never used a torque wrench on spark plugs. I use a small ratchet grasped at the head and that limits the torque I can apply. Snug and that’s it. Never had a single issue and I’ve been running aluminum heads since the 80s and changing plugs every weekend on some of them. I don’t understand why people insist on cranking them down like that as if it’s a load bearing fastener.

I sure don’t understand why anyone would tighten plugs to 15 ft. lbs when the spec given is 11 ft. lbs. The lower number is perfectly fine and if a 1/2" drive torque wrench was used then why even assume that 15 ft. lbs is actually 15; maybe due to torque variation in the tool the plugs were really tightened down to 20. If the threads are good then a measly 5 ft. lbs should hold them just fine.

When you’re down in the very low ranges of torque a high quality, 1/4" or 3/8" should be used IMHO.
Personally, I don’t use a torque wrench. Repetition helps develop a feel for it and that’s a lot more trustworthy than a torque wrench.

For an example of people thinking the spec given is not enough and suffering problems caused by overtightening, look no further than a common problem the old air-cooled VW Beetles suffered…
These cars do not use head gaskets; it’s strictly metal on metal. The torque on the cylinder head hold-down nuts is about 20 ft. lbs and many people could not believe that 20 could possibly be correct for something like this. So, they ram them on down and this led to cylinder head studs pulling out of the block; either at the time the nuts were tightened or as the engine was run.

Well, at least two other plugs had loosened up.

I use a 3/8" drive ratchet. I don’t own a 1/2" drive spark plug wrench. But it’s possible the real problem here is antisieze lubricant. It seems like when I use that, for any given torque, it’s going to drive the plug into the head more than you think. So that could be the issue.

In any case, the garage that did the work had the other plugs in so tight that I can’t even budge them now. I am kind of mad about that.

To clarify, I put the plugs in with about 15 ft lbs and antisieze; the shop checked and decided they were too loose, and now I can’t budge 'em.

To make matters worse, perhaps, the shop insists that the sound is on the back of the engine, bottom end, middle cylinder (Ford numbers that one cylinder 3). But I’ve been checking, and I think the sound is from #6 (front-right as you look in the engine compartment).

In any event, I’ve found a pair of heads, with lifters, HLAs, cams, covers, and a few other parts, with 80k miles on 'em, for $200. I almost think I could put them in as-is, but I wonder if a grind and new guides is in order.

The torque figures given in the manual are for dry threads so anti-seize may have contributed to your problem. The OE plugs were probably nickel-plated to prevent seizing and may also affect torque figures. That is another reason to use the recommended plugs.

This is an interesting thread about aluminum head inserts. Be sure to click on the TSB link and read Ford’s comments on head inserts. JohnG’s comment on spark knock is interesting.

I’ve heard of this, and this is an entirely different problem. The Duratec is not related to the Modular V8. This Escape had at least 6 threads, maybe 7 or 8.

I want to know if we’ve resolved the original question. My opinion is, yes, it can lead to a head replacement. Anyone else agree?

I disagree. Any spark plug hole is repairable no matter how bad it’s stripped out and a cylinder head replacement is not necessary.

As to the link and TSB being issued, a TSB being issued by Ford does not mean in any way, shape, or form that the problem is related to design if that is the inference.
IMHO, it’a all about someone overtightening plugs or allowing them to freeze in the threads, which can lead to thread damage when the plugs are finally removed.
My Lincoln Mark has the 4.6 DOHC, aluminum head engine. It has almost 220,000 miles on it and I pull the plugs out of that car about every 15-20k miles for tip inspections. I have yet to see a sign of failing plug threads.

I’m afraid I don’t understand the comment from the tech administrator on the site provided through the link.
He states that “I have never seen a gasketed spark plug on AL head unless we are talking about Small Gas Engines (Honda, Briggs and Stratton, Tecumseh, etc”.
That’s going to fall into the breaking news category to me. Real breaking news.

One common problem that exists, among DIYers and even some techs, is that many use a plug socket and extension to start a plug in the threads and this is a no-no IMHO. A short length of vacuum tubing should be inserted onto the end of the plug and the plug is started into the threads by this method. This is especially crucial given that many plugs are located in the bottom of deep wells in the valve covers.

One thing I should have added is that a Heli-Coil or thread insert will actually make the cylinder head stronger in this area since the diameter of the HC or thread insert is much larger. It will require considerably more force to to ever strip one of those out.

I made reference to the VW air-cooled cylinder head studs pulling out of the engine blocks earlier. This was solved during a rebuild or repair by using studs with oversized threads on one end or inserts referred to as “case savers”. This provided a larger diameter thread and served the same purpose as HCs or thread inserts in the spark plug holes.

The old antique Harley Davidson sidevalve, or flathead, motorcycles used aluminum heads that came with considerably oversized inserts in the cylinder heads to prevent this very problem. The factory plugs were about 4-5 threads deep but had 18MM diameter shanks on them, which is very large. The inserts were around 30MM in diameter so you can see the amount of force it would take to pull an insert out of one of htose heads.

Now, this is interesting because your engine is the modular, which is the one that many people are having problems with. How many threads hold your plugs in place? I’ve heard it’s 3-4 on the early ones.

I am pretty concerned about what this shop is doing. I’ve listened to this engine very closely, and it’s obvious to me the sound is coming from the #6 cylinder, top end, and they insist it’s from the bottom end somewhere. I simply don’t believe them.

Added to this, I’ve tried to remove one of the plugs they “tightened” for me, and it is SO tight, I can’t budge it. I think they’ve set me up for the next plug failure. I’m inclined to keep driving it, and when one of the other plugs ejects, tell them they owe me two replacement heads.

Replacing these heads is a very difficult job. I will not do it myself.

And, really, I do think a plug hole can get damaged beyond repair. I don’t see how you’d helicoil one of these things twice.

I think the ticking I’m hearing is leakage around the plug, because I just don’t think they did it right. I selected the wrong garage. They’re over there right now trying to find something wrong on the bottom end, and I don’t think they’ll find a thing there.

I don’t know how many threads are in the engine; the holes are in the bottom of some pretty deep wells and I’ve never had a reason to go in there. The car/engine is a 1994 model.

Fords generally use taper seat plugs and taper seat plugs do not have to be tightened as much as gasketed plugs. Speaking as a tech, I never use a torque wrench. My method for tightening spark plugs is to use a stubby ratchet (3-4" long) and palm the ratchet while tightening the plugs. All of the force is concentrated on the head of the ratchet, not the handle, and this prevents overtightening while never causing a problem.

I still disagree that a head can be damaged beyond repair, although if someone can rip a Heli-Coil out by overtightening then they should probably be at work in pro wrestling. It’s still repairable though.

  1. Please note that I posted the link with the TSB with the intent of informing of an alternative thread-fixing system that may have some advantages in terms of preserving the heat-transfer characteristics for the spark plugs. Whether this is a real problem, I don?t know. It seems to me that if ferrous metal threads are used, it might require installation of an odd plug. Would that be a problem?

  2. ok4450, what aluminum head engines have you seen that have gasketed plugs? I would assume that the commenter works mainly or even exclusively on Ford products so maybe that is the reason for his limited observations.

  3. MikeM95831, at least one of those kits, Biggert, Timesert, I forget, says that they will be good for repairs of heads previously repaired by coils. I can?t say I have tried it.

As far as I know most al. head engines use gasketed plugs and tapered seat ones are the mutants.
Here’s one example. For some reason this thing would not let me post multiple links.

Go to the site, pick a car and year, and take a look at the pics.
In regards to the following personal and family cars currently owned and previously owned, all used gasketed plugs on aluminum heads. (Varying years and models)
3 Subarus
2 Nissans
3 Mitsubishis
4 VWs
Current Lincoln Mark is the only aluminum headed engine with tapered seat plugs. Never seen a tapered seat plug on any foreign car I’ve ever worked on, including Honda, Fiat, BMW, Renault, Volvo, etc. which could be added to the above list.
Maybe there’s something I’m missing here.