Skip the auto shop - Our mechanics make house calls

Q: Had a spark plug blowout, but the threads are fine and intact, plug was able to screw right back into place. What can cause that?

asked by on

So I was driving along and heard a loud pop, and stutter in my engine. I thought I had hit something, but I then noticed my car spitting and popping. When I ran a code scan I came up with cylinder 7 misfire, when I checked cylinder 7, the spark plug was out of the cylinder and the coil was broken where it gets a screw to be held on. The coil boot was torn, so it was about 1am and I was about 20 miles from home. I luckily had the tools in my car, I ended up putting the spark plug back in and it fit fine, the threads weren't hurt at all. I put the coil back in and hoped it would last until I got home. The car didn't spit or pop at all the rest of the ride. My question is, what causes a spark plug to pop without stripped thread? I have had problem with this cylinder before, last time there was oil in it and covered the spark plug. Should I be looking at something specific? Any thoughts or ideas would help. Thank you very much for taking the time to read about my woes. ;)

My car has 160000 miles.
My car has an automatic transmission.

A: This is a known problem with this engine an...

This is a known problem with this engine and Ford/Mercury has a technical bulletin for installing an insert into the spark plug hole. You may not think that you don’t have a loss of threads in the hole, but you do. The heads only have about 4 threads for the spark plug hole. The head is made out of aluminum and will wear out if the spark plug is not tightened to exact specification the first time a plug was in the hole. When the plug moves it will wear the threads until the plug flies out. The next plug goes in fine and you might think that it’s held in securely but it is not and soon flies out.

The only fix is to put an insert into the hole or have the head replaced. The technical bulletin I mentioned for your vehicle is the one from 07-21-2 dated Oct. 2009. I’d recommend having a certified mechanic diagnose your particular issue, they will be able to inspect why oil got into the spark plug well in the first place and make any necessary repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Engine overheating - 2009 Buick Lucerne

Hello. The thermostat is located inside the housing opposite the engine water pump. The radiator hose and housing must be removed to gain access and new coolant should be added when the work is done. I recommend having an expert...

Q: Car idles when shifted into any gear when foot is removed from clutch

Hi there. This sounds like you have a failed clutch disc or pressure plate. The clutch disc provides the frictional surface for the flywheel and pressure plate to grab and move the vehicle. The input shaft of the transmission is...

Q: Lights not working

It appears that your Mercury Sable is having electrical problems with its lights. If you would like to investigate this yourself, attempt to locate the fuse box for your Mercury Sable. If you do not know where it is located,...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...