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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
Comments: To: Chris Fall <cpfall@ucdavis.edu>

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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