My sister has a 2008 Navigator with 110,000 miles. I recently changed out some brakes and mentioned to her about getting the plugs serviced. She asked our local Lincoln dealer and he said not to change the plugs until you start having issues. I find this very wrong. I know Ford had plug problems with the earlier model 5.4 engines but how do I tell if the plugs in this Navigator are the problem plugs?

 

Whether they are problem plugs or not, it really doesn't matter with 110k. If they break on the way out they break, doing it now or later won't effect the outcome at this point.

 

So it looks like this might turn into an issue either way.