<VV> Spark Plug Diagnosis Question

Jeffrey B. Aronson jrh at foxislands.net
Fri Nov 26 22:57:01 EST 2010

On 11/26/2010 10:36 PM, Mark Durham wrote:
> Jeff, we'll have to see who responds, but I think #6 might be the
> hottest cylinder of the 6, because it is over the longest exhaust log
> and is also back in a corner. Its also the farthest from the
> carburetor, like #1 and will run a bit leaner. #5 probably also runs a
> bit hotter but not so much that you would notice.

That makes sense.
>   Its interesting that
> they put the CHT probe at the other end of the engine where it stands
> to be cooler, in #1. There are guys out there that have installed 6
> cyl chts and could let us know if I am right.
> With a engine that has a ducted fan on top, supposedly all cyls get
> the same amount of air, and that may be true in theory, but things
> like cylinders not being de flashed, or the fact that the engine is
> closed off on the bottom and only lets air out when the engine gets to
> a certain temp, and that cylinder is the farthest from the outlet, it
> stands to reason it is hot.
> While looking at the plugs, have you compared them to plug charts off
> the internet?
Yes, I h ave, and I've checked a lot of plugs on British cars for hints 
of running condition.
> If the plug is completely white and has little metallic
> globs on the ceramic, that cylinder is close to or at detonation, and
> you may want to look at timing, gas quality, etc.
The tip of the plug was quite white, but I did not see any metallic 
globs on the ceramic; that part looked fine. If timing were an issue, it 
would logically affect all the plugs. Gas quality is an issue on the 
island, as I cannot get premium gas here. But recent tanks of fuel have 
been purchased on the mainland, where the car was in regular highway use 
for a few months. So it seems less likely that fuel is the issue on that 
one plug.

I will check the plug after a few hundred miles to see if there's any 
change. Thanks for the tips and the suggestions!

Jeff Aronson
Vinalhaven, ME
> Mark Durham
> On Fri, Nov 26, 2010 at 9:17 AM, Jeffrey B. Aronson<jrh at foxislands.net>  wrote:
>> Hi Experts,
>> Before Thanksgiving I completed an ignition tuneup by installing new
>> spark plugs in the Monza 110/4.
>> One question:
>> 5 of the plugs [AC's from Clark's] looked as expected, as they were last
>> changed in the late spring - brown with no oil or carbon deposits. #6
>> plug looked quite white, as if it ran hot. In September, when replacing
>> the flywheel, Ron Tinkham and I noticed that the oil cooler was rather
>> clogged up, so we cleaned it out. If that was a cause of hot running,
>> I'd assume that all the cylinders might run hot, too.
>> What might cause the #6 plug to burn white at the tip like that?
>> This time, I've tried Champion plugs to see if there's much difference
>> in daily use.
>> Thanks in advance,
>> Jeff Aronson
>> Vinalhaven ME 04863
>> www.landroverwriter.com
>> '66 Corvair Monza Coupe 110/4
>> '66 Land Rover Series II-A 88" SW
>> '80 Triumph TR-7 Spider
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