Date: Tue, 4 Jan 2000 16:13:57 -0500
Reply-To: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Subject: Spark plug heat ranges
While my knowledge of the subject is somewhat rudimentary, I think I can
'splain it okay.
Your spark plugs are essentially a pair of air-gapped electrodes, insulated
from one another by a ceramic cone. They operate in an INTENSELY harsh
environment. The combustion chamber is at times arctic frigid, drippingly
humid, desert dry, blazing hot, full of acidic vapor, full of fire, full of
exhaust, full of oil mist, etc.
All the while, the spark HAS TO jump from one electrode to the other,
without fail. In order to achieve this, the spark plug is designed to
retain a certain amount of heat from the combustion process to essentially
"burn off" any contaminants that come in contact with the ceramic insulator
cone that holds the center electrode. If it didn't burn off those
contaminants, the insulator could be covered in a conductive substance,
(moisture, oil, etc.) and the spark plug would stop firing. Are you with me
so far? Good.
The heat range is simply a measure of how much heat the spark plug retains.
Certain engines don't need very hot plugs (like a 5, 6, or 7)...putting in
plugs that retain too much heat causes the plugs to melt or disintegrate.
Other engines need hotter plugs (8-10)...putting in too cool a plug will
cause erratic firing, and missing, particularly at idle.
As your motor ages, *typically* you need hotter plugs, as you have more
'crap' in the combustion process; your rings and valve guides allow
water/acid vapor and oil into the combustion chamber, potentially
contaminating the plugs. Most FLAPS can help you decide which heat range is
best for your motor if you bring in the used (10k+) ones from your motor.
You may want to check out a book from your library, or scan that newfangled
internet thing for pictures of used plugs, and what various appearances
indicate.
Finally, as a general rule, stick with Bosch for your VW ignition needs
(EVERYTHING: wires, cap, rotor, etc.). While NGK, Nippodenso, AC-Dulco, and
Chumpion all make plugs that will fit in the hole, I had more problems with
VWs I tried these plugs in. Bosch has a new platinum plug that is supposed
to triple your mileage and double your horsepower or they'll buy you a new
car. You might wanna try these. Their regular copper-core ($1.20) is a
great plug as well.
Cheers.
G. Matthew Bulley
Bulley-Hewlett
Corporate Communications Counselors
www.bulley-hewlett.com
Cary, NC USA
888.468.4880 tollfree
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-----Original Message-----
From: Chris Fall [SMTP:cpfall@ucdavis.edu]
Sent: Tuesday, January 04, 2000 2:45 PM
To: Bulley
Subject: Re: one distributor post corrodes, was: try again
thanks. I really have never understood SP heat range. can you tell me what
it means?
Chris Fall
Institute of Theoretical Dynamics and
Department of Molecular and Cellular Biology
University of California, Davis
cpfall@ucdavis.edu
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