I know it's the middle of winter, but I was having the worst gas mileage of any Prius I have owned. With this 2006 Prius, I was averaging 35mpg. I could get better than that in my Highlander. I was averaging 62mpg city/highway combined with the first gen Prius and better than 70mpg with my 2012 Prius I gave to my ex. And it was getting worse each week. Yuck! Then I changed the spark plugs and oil: That's just 60K miles. The insulators appeared to have a light contaminated layer well baked into the surface. That may explain why the engine felt rough. The end of the threads had noticeable carbon build up. I replaced them with the cheapest $3 platinum plugs at the store. Now the engine runs very smooth and doesn't seem to rev as high going up hills. It even doesn't seem to come on all the time either. Weird. So now I'm easily getting 65mpg, which is good enough for me. Maybe changing the oil had something to do with it. But I'm glad I got this done.
Did you change the oil weights by chance? This would help explain some of the mpg increase. What grade gasoline do you use? Is it greater than 10% ethanol? Also Toyota recommends the OEM Denso Iridium plugs. You may want to try these at your next change especially if these do not last very long.
appears that some donkey forgot to nail his four shoes home, the sealing washer on the sparkplug does not appear compressed, hence the leakage of combustion gases. OE spark plugs in prius I have known will do 150,000 miles easy. Top shelf fuel is the secret.
I disagree on both counts. It looks to me like those sealing washers are the soft metal type and not the "crush" variety. Second, I don't think that "top tier" fuels are the solution to anything......except maybe keeping the oil companies profits up. But I fully understand that a lot of people have bought into those marketing claims. And lastly, I would never leave a set of plugs in an engine for 100,000 miles; 50K is more like it. You need to have a look every so often because they provide a lot of clues as to engine health.......and since they are out, they might as well be replaced.
