Plug heat range measures how well the plug sheds heat to the cylinder head,
and this depends on the size and shape of the ceramic insulator. Hot plugs
shed heat slowly, because the contact between insulator and cylinder head is
relatively small and far from the center electrode. You run hot plugs in a
cool-running engine (e.g., many short trips). Because the plug retains heat,
the electrode is less likely to foul. Conversely, cold plugs shed heat
quickly, because the contact between insulator and cylinder head is
relatively large and close to the center electrode. You run cold plugs in a
hot-running engine (e.g., race engine). Because the plug sheds heat, its
electrode is less likely to burn away.
So if all your plugs are fouling, switch to a hotter plug. If they are all
burning their center electrodes, switch to a colder plug. If only one plug
is fouling, and you have tried swapping plugs between cylinders, then the
problem is elsewhere.
Craig Foch
1963 TR4 CT 22268 L
1964 Ford Falcon Ranchero
1988 Daihatsu Charade (LJC: 993 CC 3-cyl)
> From: "Randall Young" <ryoung@navcomtech.com>
> Reply-To: "Randall Young" <ryoung@navcomtech.com>
> Date: Wed, 29 May 2002 22:49:44 -0700
> To: "john donnelly" <pdonnel1@san.rr.com>, "'triumphmail
> list'"<triumphs@autox.team.net>
> Subject: RE: One Black Plug
>
>
> Plug heat range is a fairly confusing topic, at least to me.
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