Spark plug test success! (A-B-A-B = 2% gain with lower heat range plugs)

[hat_man]

So what is the current (no pun intended) state of this discussion? Colder plugs might be better for FE but harmful to the engine? I am interested in this but still a little confused.

[nemo]

Colder or hotter depending on the situation may or may not improve your mileage.
From the NGK website:

The spark plug firing end temperature must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called “Thermal Performance”, and is determined by the heat range selected.

In nubbzcummins case.

With colder plug it would hold 2 deg more timing pulling a hill resulting in more power and less downshifts to 5th on some slower inclines which causes real time mpg go down.

The long term effect of running this plug has not been determined, being colder it may not fully burn off deposits and require more frequent replacement or a cause long term reduction in fuel economy. The most common reason for changing heat ranges is engine modifications an example: raising the compression. A car that is burning oil might benefit from hotter plug to reduce fouling.


Go here for a spark plug overview:
NGK Spark Plugs USA

[ECONORAM]

Very interesting thread. I am curious because the wife's 08 Avenger will knock on 87 octane; I've been running 89 for a couple years now to avoid that. It's a 2.4L that runs 10.5 CR. Never thought of running a range colder plug.