Just swapped the plugs out at like 119xxx miles. Ive done all the maintenance in the book myself and I havent really had any problems. 2010 Gen 3 10k mile syn oil changes, and the car consumes about 1 quart per 10k. I did notice that the car in the last couple months would jutter for like 10-20 seconds on start up once or twice and then go back to normal. Like an aggressive jutter but its only ever done it twice. So I'm not sure to say about that. Cold weather? How do these plugs look for 120k? I've never really been the plug reader since I've never kept an engine long enough to worry about it.
What's important on those plugs are the conditions of the centre electrodes. You didn't display that part if the plugs. If they appear tan colour, means they were firing properly. But if black, and fouled, they aren't firing properly. From seeing the ceramic insulation on the plugs, those plugs have being exposed to tremendous heat from the cylinders that's why they are black on the electrodes. The black oily deposits on the threads also tells me your engine MIGHT have excessive engine oil sipping into the combustion chamber?!
Excessive heat points to the EGR again. 120K miles is prime time to clean the intake manifold, the complete EGR circuit and install oil catch can. Sooner would actually be better. It's frustrating: the stuff Toyota never mentions. Check out @NutzAboutBolts videos, pinned in the 3rd gen maintenance forum. Also lots of info in this thread: EGR & Intake Manifold Clean Results | PriusChat
Stop the oil from getting in your engine and get an oil catch can. Our 2010 prius with 118k has not had the egr system cleaned and has not had one cold start knock. I believe oil being burned causes the egr system to foul up. Your spark plugs look like they have been burning oil, oil coming from the pcv system. Remove the intake manifold, clean it and install an oil catch can before you get a blown head gasket.
Yeah I really wondered why the plugs were so burnt on the shafts above the threads. This car has also never really gotten spectacular mpg since I've owned it (bought at 92k) so maybe the pcv/EGR/manifold could be something to check as well. This is the only car I've ever owned where I haven't been able to get the EPA Mpg rating! I probably average between hot and cold weather 46 mpg city and 42 mpg highway (68 mph gps) when I'm trying so about 95% of the time. Thats with 50 psi tires and a little bit of aero improvement (pass mirror delete/wiper delete, antenna removed etc... some easy stuff) and I try not to even use the heater in the winter so the engine will stay off longer. So on the EPA's scale im getting 88.4% of EPA rating. I had a 96 Civic 5mt that got 42 while it was rated for 36 combined. I'm going to try the cleaning and some new LRR tires and see if it improves. Also to note I've only had the jutter three times in total. One time around when I got and one time in the fall, and one time this winter and the car has never had a cel.
Thanks for mentioning PCV. I didn't directly mention, nor @danlatu, and it's likely what instigates the EGR carbonning up.
Wow so I found a decent deal on some bridgestone ep422 tires (low rolling resistance tires). 185/65/15 which arent 195s but no big deal. Bought them for 301 shipped, and was able to swap out my cooper cs3's. Went from 46mpg city to 51 currently and its been rainy and wet versus the dry weather we had been having for my cs3 averages. Looks damn good! Both sets of tires at 50 psi too. Need to get to the pcv stuff once it warms up. Going to pick up a Jon boat three hours away in the Prius so i'll be interested to see how it does. lol Makes me excited for warm weather values again.
