Originally Posted by RogerRamJet
Put some $1.99 Champion OEM plugs in last week. Getting 2+ more mpg after the switch. Added synthetic oil, too. But I'm thinking the plugs are where the real gain is.
Actually synthetic is likely where your gain came from. I can't explain why or how, but EVERY motor I have ever switched has seen at least a 1-2mpg increase on average. EVERY one. Not here or there, hit or miss, consistently. 14 motor's over the last 8 years or so. (had a lot of cars LOL)
Originally Posted by 11silverslt
I just changed my plugs today, bought them from the dealer and they were Bosch plugs in Mopar boxes. All was going well until the coil boot was seized on the rear most plug on the driver side of the engine, well we all know what that means a trip to the dealer for a replacement coil, because no parts store stocks coils for my 4.7l engine. Had to go to two different dealers and bought two just in case. Good thing because I broke another one finishing up. While at the dealer a tech said they change the plugs when the motor is real hot to avoid the boots seizing onto the plugs. Truck runs good now with al the new plugs and air filter and coils and it only cost me $ 147.01 for a tune up and all day Saturday running around. Don't know about the mileage yet but I was getting 18 + on the highway before so we will see.
I would not let that tech or anyone from that dealer anywhere near my truck...EVER.
Pulling the plugs on a hot engine is a good way to pull the threads out of an aluminium head. Metal expands and contracts with heat/cold. Since Alumnium dissipates heat faster than most other metals (including the ones your plug's threads are made of), they expand at a MUCH slower rate than the plugs. So the plug threads are expanded while the heads threads are not expanded as much. Removing a plug at that point will almost certainly strip the threads in the head.
When that happens, sometimes you get lucky and there are a few threads left that can hold the plug in place, but then there are metal shavings in the engine. If you are unlucky, the head has to come off to be re-tapped.