Cylinder 4 spark plug keeps blowing


I have a 2001 Dodge Ram 1500 that I bought used a couple of years ago. About every 20k miles (120k miles on it now) I get a check engine light and upon diagnosis it’s the 4th cylinder spark plug fouled out, every time. I change the spark plug, but the old ones are always identical in damage. The porcelain has cracked on the spark plug. Any and all help is greatly appreciated!

Pics below

Here are pics of the spark plug, sorry about the quality. You can see the vertical crack in the porcelain.

Is there something about the location of this specific plug that makes it difficult to install? I’m wondering if the plugs are sustaining some kind of damage during installation that causes them to fail.

I can’t see the crack, is it in the electrode side of the plug, inside the cylinder? That seems to be the case as the 3rd pic is just the inside of the plug. You may have a “hot” spot in that cylinder causing pre-ignition. Do you hear the engine knocking?

Check out the location of the knock sensor. If it is easy to find, make sure the connector is attached and perhaps even change out the sensor.

If the pre-ignition is just in the one cylinder the knock sensor may not be reacting to it. You may need to run a higher octane gas.

Since this is an older truck some of the internal cooling passages maybe plugged. You might want to see if you can really flush out the old coolant and put some chemicals in the block that are designed to clean out the dirt and crud that might have build up inside the block.

In the end replacing a plug every 20K isn’t that big a deal. Carry a spare and the needed wrenches and you can change it in a parking lot if necessary.

I had a similar problem on a Ford Aerostar some years back. The problem was a,hairline crack in the cylinder head that would let in just enough coolant into the cylinder that when it hit the plug, it cracked rhe porcelain around the center electrode. The dealer finally pulled the cylinder head and found the problem. Fortunately, the Aerostar was under warranty and because, over time the coolant had scored the cylinder wall, the entire engine was,replaced.

I too suspect thermal shock.
However, I recommend that you switch your sparkplug brand. I’ve had a lot of problems with Champion sparkplugs in the past. I won’t use them anymore.

Champion is what many Mopar owners swear by as it is the brand used by the factory.

Really? That’s a surprise. My experience with them hasn’t been good.

Besides the more likely ideas above, ignition timing might be involved. Especially if it is too far advanced. Have your shop verify the ignition timing is correct for the rpm range you typically use. Also, check ther vacuum ports, esp those that are situated close to number 4. Make sure there are no vacuum leaks there. A leak could draw in unmetered air and lean out the mixture enough to make it burn too hot. Finally, you could try switching to a higher octane rated fuel to see if that helps.

I tend to agree with thermal shock. Is the EGR system operative? It’s quite possible to have an EGR fault without setting a code; mainly if the passages are clogged.

Anti-freeze can also cause it but in the cases I’ve seen the side electrode of the plug usually appears to be bleached white or bone colored. That could vary by car I suppose.

Just my 2 cents, but I refuse to put a Champion plug into anything other than my mowers, Weedeaters, and chainsaw.
I ran into a rash of bad Champion plugs over 25 years ago and haven’t used them since. Some of those plugs were stone dead right out of the box and others had symptoms which would caused bucking after 75 miles of use and so on.
They caused me a lot of grief and time, a.k.a. money, and I haven’t touched one since.

I am not aware of an EGR system being used on any Magnum engine of that period and the ignition timing is not adjustable.

A common problem that could cause spark plug damage is a vacuum leak in the bottom of the intake plenum. Disconnect the PCV valve from the valve cover and plug the hole, connect a vacuum/pressure gauge to the crankcase breather hose and check for the presence of vacuum after a short period of idle. There should be a mild pressure, if there is any vacuum the belly pan under the manifold is leaking.

I would like to see what the other plugs look like.

The theory applied to my 91 Explorer was a coolant drip onto the plug from the head gasket.
After shutting down , when the plug is still hot, the seep from a bad head gasket would get on the plug , and as others have just said , , thermal shock.
The exact same plug would be cracked every time.

I also think its a very small coolant leak because of how clean the plug tip is, but like OK4450, the ones I have seen looked like they just came out of a sandblaster. Maybe this is just a much smaller leak that I’ve seen before.

Check if the spark plug is the proper heat range for the engine.


IMHO Champions are JUNK… Though there could be another cause for this…what that is I dunno. The plug isnt excessively clean so I dont suspect burning coolant… If this has happened to the exact same cylinder more than once…then it is likely not the plug mfg…tho I still do not like Champion plugs.

I would need to go to the drawing board on this one… You sure nothing is leaking onto the plug externally ?


Maybe the quality of Champion plugs is related to the mentality of their executives.
Here’s a excerpt from Smokey Yunick’s autobiography describing when Champion execs visited FL to consider supporting NASCAR:

“I remember Champion Spark Plug (one of very first to put money in NASCAR). France met Champion’s executives at the Eastern Air Line plane with an elephant. The elephant had a thing like a pickup box strapped on it’s back for them to ride in, and came equipped with two hookers and booze. The two Champion “big shots” (Dick McGeorge and I forgot other cat’s name) rode elephant to the Streamline Hotel, a trip of ’bout three or four miles. I’ll let you guess how that ended. Well Champion put lots of money in NASCAR for ’bout 40 years and in the end they got screwed out of a building they built and paid for at the Daytona track. But don’t cry many tears for Champion. During the last 40 years it’s been run by a bunch of incompetent assholes, and maybe that’s best way to purge a defective outfit.”

So hopefully this helps…I have 2 dodge 4.7 and had 1 3.7 (same engine minus 2 cyl)

1st is an 04 ram 4.7
2nd is an 02 ram 4.7
3rd was 99 ram 3.7

In ALL these I would occasionally get random misfire codes (champions from autozone), pull everything apart, used scan tool to test fire coil packs, test/check sensors etc etc

Replaced plugs, fine for a while then start again, all 3 right around 20k miles on plugs…changed plugs another 20k then random misfire…this continued for 2 yrs on the 02 and 04 (sold 99)

For the 04 I went to Orileys and bought champs instead and on 02 bought set of Ngk from the zone

The ngks lasted about 40k the champs from Orileys about the same

So I’ve done some thermal checks with a dedicated temp sensor

Neither truck has ever overheated or run hot, both have factory thermostats, both thermos are opening on temp, coolants flushed., pressure test no leaks and on and on

So what we’ve found, with the coil on plugs in the 4.7, the thermal shock is coming after shut down

Metal to metal in the head the plugs are close to 300f, the exposed ceramic before the coil boot is about 225 when running, under the boot is about 295

When shut down occurs the metal thread on plugs after 15min is around 275 plug ceramic 160 and under coil boot is 260ish

We used heat shrink around the ceramic and reinstalled the ngk, the exposed middle ceramic stays more consistent with metal thread

All this said…these engines do have a thermal issue with the exposed ceramic on the plugs

In the 04 we stuffed standard fiberglass insulation around the plugs after install before coil packs and on the 02 we bought accell yellow high heat header plugs

In the end, champions from autozone have some issues, but champs from Orileys seems less of a problem, ngks seem to not care either way, and the accell high heat yellows are going strong

Both trucks after 45k on current plugs, 1 with insulation added and 1 running high heats with no insulation