So a mechanic friend of mine just did a tune up for me today. He found that NINE of the sixteen spark plugs were the wrong size! I don't remember exactly the name of the shop where the last tune up was done, but it was one of those express lube shops that was offering a special promotion on tune ups at the time.

I bought the truck from my brother who was the original owner. And just before he sold it to me he took it into this place to get a tune-up done as a nice gesture before he handed me the keys. So I wouldn't have noticed any significant change in performance since it was the first time I was driving the truck. Truck has been running fine though. And I've been averaging 11.5mpg around town, which I've read on this forum is common.

Is there any possible consequences that I should be looking out for? I can't believe I had the wrong plugs in there this whole time! The one on the right in the attached pic is one of the seven correct sizes.

 

For future reference:
https://dodgeforum.com/forum/dodge-r...s-section.html

 

The only thing I can think of would be excess carbon build up, which new plugs of the proper heat range and reach should take care of.

 

Just a different heat range. The shorter ones are a hotter plug.