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Spark plug blew out and destroyed engine

I have an older Acura MDX with 188,000 miles on it. A couple days ago while driving down the road there was a very loud pop/bang noise followed by what sounded like 100 motorcycles around me and lots of smoke coming out of my engine. After being towed to the dealership, I am being told that a spark plug blew out, launching the thing that keeps it place into the engine where it bounced around and destroyed the engine. At least that’s their “best guess” and are now telling me that I need a new engine (total cost including labor estimated to be about $4,000). The car is only worth about $3,000. All work on this car has been done at the local dealership (where it is now) so they have records of everything that has been worked on/replaced over the last 10 years.
I read a previous post regarding a spark plug shooting out like a rocket and got through most of the comments. Here is the purpose of my post – I do not speak a mechanics language and do not know what to ask or say to the dealership to further inquire on how this happened, is that really the problem, and if so, are they at least in some part responsible for this? Does anyone here have any advice for me on how to approach this? Thank you for your time.

A spark plug blowing out of an engine will not destroy it.
If the spark plug came apart and a chunk of the plug fell inside the cylinder then yes severe damage can occur.

You need to find out if a hunk of the old plug is inside the cylinder and maybe ask them if they have a borescope that would allow you to eyeball what’s inside that cylinder.

Offhand I can’t lay this on them at this point.


I agree with @ok4450 completely. And, just based on the forces involved, it’s much, much more likely that the sparkplug went flying out of the engine than that it disintegrated into the engine. Things happen, and even odd unusual things happen sometimes. Did you recently have a “tune-up” where the plugs were replaced? Failure to fully tighten a plug can lead to the launching of a plug out of the engine.

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I am thinking the spark plug blowing out, is part of a much bigger picture.

The only way I know of a spark-plug blowing out could destroy an engine is if you kept driving and gas/air mix is still being injected into the cylinder. Without the spark-plug to ignite the gas the unburned gas washes the cylinder walls of any oil and the piston going up and down will destroy that cylinder wall. Not to mention the raw gas now collecting in the oil. However in order for this to happen you’d have to drive it for quite a while after the plug blew out.

I know the sound of an engine running after a spark plug flies out can sound really dramatic but likely there was no damage done to the engine. In most cases just replacing the spark plug and possibly the spark plug wire will fix it.

What year & engine is the car? If it’s coil on plug there may be a little more involved.

My daughter’s car did this. No damage, just put the plug back and torque it to the proper spec. More than likely, the plug is still in the wire/coil boot. Ask to see the plug or what’s left of it. You can pay $50 and have it towed to get a second opinio.

If a spark plug blew out of a head, it usually means the spark plug threads in the head were ripped out also.

And since these are aluminum heads, this is probably what has happened.

The question then becomes, is it worth it to remove the heads on a vehicle with a 188,000 miles on it to repair one spark plug hole?

Or is it possible to repair the threads in the head without removing the head?


First, I’m not sure we have a clear understanding of exactly what’s wrong. There may be a misunderstanding here. Can you quote for us exactly what was written on the shop order? Were there other mitigating factors?

A plug blowing out of its hole won’t destroy an engine, but I’ve read a number of posts wherein posters were told that an oil pan needed to be replaced just because the drain plug hole was stripped of its threads. And there may have been other things involved as well in the diagnosis and recommendation. So anything is possible.

If that is their “best guess” you deserve a second opinion from another mechanic. If that plug went flying out of the engine, I can’t imagine what would be left to fall inside the cylinder walls and do that much damage and ruin the whole engine. If that thing disintegrated while still seated than it’s another story, but still I can’t see how it can destroy the engine.

Why not just ask them to put in another plug and start the car while you there? It’s 5 minutes of work and shouldn’t cost an arm and a leg. If the engine is indeed destroyed I would consider a junk yard engine. I replaced a failed Honda Accord engine once for about $1600 and the junk yard people did all the work. Never had any engine problem, but the car was later totaled in an accident.

Some of the earlier Ford Triton 2 valve V8 and V10 engines were known for blowing out plugs

While some of us disagree as to WHY occurred, I think we CAN agree that a timesert fixes the problem . . . and it would probably also work for OP’s car

I’ve got a feeling the plug blew apart not out and fragments went in the engine. Happened to my BIL many many moons ago and he actually got compensated by the plug manufacturer. Don’t remember the brand plug but he always buys Fords.

I believe autolite made the factory Ford plugs . . . ?

Yeah but I don’t know if that’s the brand he used or not.

The only way that this plug could destroy the engine is if it broke apart and parts of it fell into the cylinder…scratching the cylinder wall to the point that the rings will no longer seat.

If that plug is still in one piece…that is not the problem.

The only damage a blown out plug normally causes is either a Time-sert or Heli coil is installed to repair the threads.
I have have found the ear broken off of the coil in engines with “coil-over” plug configuration. But I’ve found these can be fixed if you want to take the time.

I suppose there could be other freak damage, but it’s unlikely.

I’d insist that they show you the damage and any good shop will have a borescope to show you the damage in the cylinder. They ,may just be trying to scare you into buying a newer car from them.


I had an engine destroyed by a spark plug once… under warranty. 8 dyas before the 24,000 mile powertrain warranty expired. The electrode was hollowed out and there was a 10mm hole in the piston the plug came out of. If the electrode, for some unknown reason, had disgorged its melted inners, that would certainly burn a hole in an aluminum piston. GM replaced the shortblock under warranty, but it took 5 weeks to GET one! I started buying Fords after that incident.

I replace those coils . . . I don’t spend time trying to reglue the mounting ears

Besides, coils don’t last forever, and it’s not going to break the bank

I think it is more like the engine got destroyed and the spark plug blew out. It is all about the way you say the story.

@db4690 I would have passed on repairing those coils too, but it was my nephews truck.
Between him starting a new job, saving for his upcoming wedding, and the day to day bills he was a little short on funds.

He had bought the truck used and had not done a spark plug change on it yet.
When he blew the first plug out…I heli-coiled it and I thought we were done. We didn’t have much time so we left changing the rest of the plugs to another day.
Within a month he blew out two plugs at the same time. When I looked closer almost all the ears were broken off the coils that we hadn’t touched.
It looked as though the previous owner would swap the good coil from a good plug to the one he blew out. Maybe he thought that that little bolt would help hold the plug in.
We bought new coils for those two plugs and I repaired the broken coils for use if any more plus got blasted out of the head.
It’s been a year and so far we have not needed to heli-coil any more than those original three, but I’ve got those coils just in case.


I may be wrong about this . . . .but I think the only long-lasting repair on that particular engine is Time-sert

Meaning, occasionally some other brand inserts blow out, and Time-sert seems to be more durable

The real problem with the time-sert kits is they are REALLY expensive

In fact, there are 2 time-sert kits

One is for when the factory threads blow out

The other is for when an aftermarket, lesser quality insert, blows out. That is known as a “last-chance” insert, because it’s obviously a bigger insert

I’ve used . . . and watched people use . . . the Lisle inserts, and I have to say they don’t work very well in my opinion. They’ll last a few months, but then they blow out. Maybe okay if you’re planning to flip a vehicle, but that’s about it