[xj] Plug deposits

Since we are on a spark plug thread I have a question about plug deposits.
When I replaced my last spark plugs (Champions) I noticed they all had a
gray ash looking deposit. I guess I don’t have a coolant leak or they would
have all been very clean. I think? Anybody know what gray ash means. They
had about 25,000 miles on them.

John
85 XJ6

I don’t know if anyone responded to you directly, but the whiter the plug,
the leaner the engine is running. At least that’s been my experience. I have
been playing with the XK120, trying to get the carbs set right, and I was
pulling plugs every couple days. They began black and very sooty, and
slowly, I leaned out the carbs until I had the rear three plugs’ curved
electrodes showing just a touch of brown, and the front three, light brown
to ashy gray. The car was almost impossible to start and ran like poop at
that point. I richened the front carb and leaned the back one just a tad
more, until all the plugs showed a medium brownish gray over the electrode,
although the insulator and base of the plug were still black. (Based on the
start-up and warm-up smoke, I think I have leaky valve guides.)

I don’t know how lean the FI engines run, but I know that to meet emissions,
more recent models run incredibly lean compared to cars 25 years and older.
Hopefully someone can give you (and me) more information what the plugs
should look like. It would be interesting to pull the plugs and check them
out.

“Mark 1” Mark Stephenson
1952 XK120 Roadster #673129 (w/XK140 engine and C head)
1958 3.4 Litre Saloon / 1984 XJ6 4.2L / 1985 XJ6 VDP
Jaguar Club of Central Arizona (USA) – www.cableone.net/jcca----- Original Message -----
From: JS4453@aol.com
To: XJ@jag-lovers.org
Sent: Tuesday, November 16, 1999 4:37 AM
Subject: [xj] Plug deposits

Since we are on a spark plug thread I have a question about plug deposits.
When I replaced my last spark plugs (Champions) I noticed they all had a
gray ash looking deposit. I guess I don’t have a coolant leak or they
would
have all been very clean. I think? Anybody know what gray ash means.
They
had about 25,000 miles on them.

John
85 XJ6

Mark, your assessment of proper color seems right to me – a warm brown (no
pun) is what I see on all our modern cars, including the Jag.

79xj6

Mark Stephenson wrote:>

I don’t know if anyone responded to you directly, but the whiter the plug,
the leaner the engine is running. At least that’s been my experience. I have
been playing with the XK120, trying to get the carbs set right, and I was
pulling plugs every couple days. They began black and very sooty, and
slowly, I leaned out the carbs until I had the rear three plugs’ curved
electrodes showing just a touch of brown, and the front three, light brown
to ashy gray. The car was almost impossible to start and ran like poop at
that point. I richened the front carb and leaned the back one just a tad
more, until all the plugs showed a medium brownish gray over the electrode,
although the insulator and base of the plug were still black. (Based on the
start-up and warm-up smoke, I think I have leaky valve guides.)

I don’t know how lean the FI engines run, but I know that to meet emissions,
more recent models run incredibly lean compared to cars 25 years and older.
Hopefully someone can give you (and me) more information what the plugs
should look like. It would be interesting to pull the plugs and check them
out.

“Mark 1” Mark Stephenson
1952 XK120 Roadster #673129 (w/XK140 engine and C head)
1958 3.4 Litre Saloon / 1984 XJ6 4.2L / 1985 XJ6 VDP
Jaguar Club of Central Arizona (USA) – www.cableone.net/jcca