Hello all, I am coming up to 120,000 miles on my 2005 Prius. It's my understanding that the spark plugs are recommended to be replaced at that time. I remember reading an article many years ago where someone tested multiple different spark plugs and found some of the multi ground electrode type significantly increased fuel economy (around 8 mpg increase over stock replacement). Any advice would be appreciated.
I really doubt that you can find a plug that will give you an increase in mileage compared to the stock plug. There is a lot of snake oil in spark plugs and oil. As long as the spark is sufficient to burn the air/fuel mixture in a smooth manner you are good to go. Extra electrodes in a low compression engine such as the Prius are not going to do much other than cost you more money. What you should do is remove your plugs and note how they are firing. Are they oil fouled or are they burning the fuel well. You should see an even medium tan to dark brown color. If they are black then they have been burning oil. 120,000 miles is a lot of mileage for a plug. Be careful when taking out the plugs to not allow dirt and other stuff to fall into the plug holes. Then hand turn the plugs when you first put them in to insure that you do not strip them. They need to be seated but we are not talking a lot of torque. I am not sure of the specs but hand tight plus 10 to 15 ftlbs of torque. Inspect the connectors to insure they are in good shape. Be gentle.
If you find that paper on MPG increase, let me know. Generally, multi-electrode plugs are considered just a gimmick, but it's conceivable that some users see benefits and some users see drawbacks as every engine model has a different combustion chamber configuration. I recently posted old "news" about a double tipped Denso plug that is energy efficient for sure. Fuel efficient spark plug | PriusChat
I will say there are plugs that do very well but the system I'm talking about is more than just plugs. Your going to have to get a plasma spark and will need to make and weld the proper plug design. Then of course test it. The ignition module will have be upgraded or changed out to supply the plasma. After that adjusting the fuel ratio and computer is nex. Redoing the fuel mapping to a leaner burn.
