Spark plugs for Chrysler 300C (HemI)

No one I have talked to, including the dealer, has been able to answer my question so I hope someone can help.

I have a 2005 Chrysler 300C (5.7L Hemi), now with 37,000 miles.

At around 29K miles I asked the dealer for an estimate of replacing all 16 (sixteen!) spark plugs. At first I was told they don?t need changed until 100,000 miles. I told him the owner?s manual indicates the spark plugs need to be changed every 30,000 miles. He was surprised that they needed replaced, but he checked and said yes, they need replaced at 30K miles and the cost was almost $200), and the dealer did the plug replacement.

Then I asked if they would put in platinum or other high performance plugs that would mean I don’t have to replace them every 30K and he said “Chrysler doesn’t recommend” using those kind of plugs. (How he knew this when he didn’t even know they needed replaced at 30K is beyond me.)

So what’s up with a high performance engine not using high performance plugs? Is Chrysler just out to get me to spend more money more often to replace the plugs or is there a valid reason for the more frequent changing.

And if I were to install high performance plugs at the time of my next change, would it ruin the engine or what?

First the authority when it comes to maintenance on any car is the manufacturer.

While the use of platinum plugs is recommended for many engines along with longer life, it may not always be a good idea. We are finding that too many times the plugs tend to become frozen in the engine and replacing them can become very expensive. I would strongly suggest following the owner’s manual. I would also suggest checking out the cost of maintenance before choosing your next car.

Platinum plugs are not high-performance. They are long-life.

So what’s up with a high performance engine not using high performance plugs?

Sorry I missed that on my first read through. There really is no such thing as “high performance plugs” There are plugs that claim they are and frankly every one of them has proven to be just a way of getting your money.

Platinum plugs will probably work fine. But I sure wouldn’t let the Dealer do it. Find a good independent mechanic…it should be far cheaper.

BTW…Platinum are NOT high performance plugs. Standard copper plugs will give you the EXACT SAME PERFORMANCE as platinum plugs. Platinum plugs just last a lot longer.

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You will not gain any benefit by using a so-called performance plug. A ho-hum copper core plug will work just as well as an Iridium plug.

Also, plugs should never be left in an engine for 100k miles, even if the factory says they can. The factory also covers their tail on this issue by having a “severe service” disclaimer; which applies to every car on the road.

And if I were to install high performance plugs at the time of my next change, would it ruin the engine or what?
It IS possible that center electrode of those plugs fell off and damage the whole thing. You’d better stick with OEM(and find another dealership if needed). Good luck.

Thanks for the responses. Much appreciated. I never realized that plugs left in for an extended period could “freeze” up and be difficult to remove. Or, that there is no such thing as a performance plug. I guess the manufacturer’s just want the public to think they are something special.

You might be correct in saying that there are no “high performance” plugs, but there are plugs for high performance applications. Fine-wire iridium are often used on blown engines. Apparently they suffer less misfire.

For the record, my 2005 RWD 300C 5.7L HEMI just hit 152K miles running smooth as silk on original plugs. Brakes lasted until 148K. This has been the most reliable trouble free car I’ve ever owned and I’m 74 years old. I’ve decided to continue running the original plugs until one destroys the engine.

Why would you want to take a chance on destroying the engine, rather than simply doing the preventive maintenance that is specified by the manufacturer?


Mike, thanks for reviving a 13 year old thread and posting something that a reasonable person would not do.


What ‘preventive maintenance’ would work on my 152K 300C engine? I read in this thread above that replacing plugs on a high milage engine (above 100K mi) was very risky and might destroy the engine. Is that not true? What are the odds my 152K 300C getting a successful plug change?


Seriously ? Any decent mechanic will just remove the old plugs and install what the manufacture calls for . Besides it sounds like you have avoided a lot of service that this vehicle should have had .

I am a 74 year old Vietnam veteran barely making it by on SS. If I were to receive a call from my mechanic stating that the plug change dropped things into a cylinder and would require removing the heads, I would have to let them keep the car for lack of funds to pay for that.


As is, I can never drive this car any further than I can afford the cash amount to have it towed back home. From my perspective, I’ve already lived 6 years past my calculated life expectancy and investing in a longer lasting 300C wouldn’t necessarily be the wisest move. That’s why I am making these strange choices.


No, it is not true.

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My hats off to you and thanks.

Even now, follow the recommendation in your user manual. The manufacturer knows best. True 16 plugs are not cheap, but will improve the performance and gas mileage over your plugs with 152K miles.

No need to run your plugs until they destroy your engine. If one of them starts to misfire it will set your check engine light.

That is not true at all. In fact our current vehicles 07 Lexus and 14 Highlander all have 100k mile plugs. Already replaced plugs on 14 Highlander once…and replaced plugs on 07 Lexus twice. My 05 4runner also had 100k mile plugs. Kept vehicle for over 300k miles and replaced plugs 3 times.