View Full Version : Spark plug question

08-08-2006, 08:33 PM
I have a 1971 TR-6. The specs. say I should use a 9Y plug, which is cooler than the 12Y I have always used (and is recommended for the later years due to compression and emission stuff, I assume). I recently saw a comment that you should use the coolest plug possible. What is the problem with hotter plugs? My car seems to run fine with the hotter plugs.

Andrew Mace
08-08-2006, 09:21 PM
There isn't a drastic difference between the N9Y and N12Y, so I don't really think one can do any real harm in using the N12Y instead of the N9Y.

Anyway, my Leyland-issued Triumph TR250/TR5/TR6 Repair Operations Manual says that you SHOULD be using the N12Y; it was only from 1973 onwards that the N9Y was specified.

08-08-2006, 11:24 PM
It all depends on how you use your car. If you do most of your driving on the interstate or highways, then use the cooler plug. If you drive mostly in the city and for short distances then you should use the hotter plug.
The temperature range of the plug has nothing to do with how hot the spark is, that is a function of your coil. What the plug heat range specification tells you is how much heat is retained by the spark plug tip. The hotter plug retains more heat at the tip of the plug so that it can burn off carbon and oil deposits and provide a more efficient spark for a longer time frame before cleaning or replacing. Conversely, if you are using a hot plug and you are doing more open road driving you may experience pre ignition or ping because the spark plug tip is too hot and actually glowing causing the detonation.
Hope this helps. /ubbthreads/images/graemlins/grin.gif

08-09-2006, 12:38 AM
RomanH, /ubbthreads/images/graemlins/iagree.gif spot on---Keoke- /ubbthreads/images/graemlins/thumbsup.gif

08-09-2006, 12:02 PM
Thanks for your help. It makes sense and I feel better about it.

08-09-2006, 12:12 PM
I just learned more about spark plugs here than I knew my entire life. Thanks