Re: {Chrysler 300} Rear Plugs Fouling

It leaks more immediately at shutdown, and sits on top of the piston until burned off on start up. Higher range plugs will not fix it. No plug can withstand that for long. The B R/B blocks are known for this at high mileage.

Danny Plotkin

-----Original Message-----
From: "Marshall Larson" <granitledge@xxxxxxxxx>
Sent: Thursday, May 29, 2025 4:23pm
To: "dplotkin@xxxxxxxxxxxxxxxxxxxxxxxxx" <dplotkin@xxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} Rear Plugs Fouling

Put higher heat range plugs in at least the two rear cylinders. If it is valve stem seals it is leaking oil all the time, not only at shut down.

On Thu, May 29, 2025 at 1:49 PM dplotkin@xxxxxxxxxxxxxxxxxxxxxxxxx <dplotkin@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Your valve stem seals are shot. My NY 440 had the same illness. The engine is tipped back naturally in the car so oil drains back at shutdown and down the valve stems it goes into the combustion chambers.

I was changing plugs twice a season until I fixed it. Not a bad job.

Danny Plotkin

-----Original Message-----
From: "Anthony Doughty" <62red300h@xxxxxxxxx>
Sent: Thursday, May 29, 2025 2:43pm
To: "Chrysler 300 Club Listserver" <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: {Chrysler 300} Rear Plugs Fouling

After about 1000-1500 miles the rear plugs on both side of the 413 in my 300H start to carbon up and fire poorly. The other six plugs are fine. The carbs have been overhauled, idle settings are shop manual correct, and the car runs really well until the carbon begins to interfere. Anyone have any thoughts or knowledge as to:

(a) why this might be happening and

(b) how to fix it?

Thanks for any help and advice,

Tony Doughty

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Marshall Larson

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