There have been times when the technicians at Certified Transmission have found spark plugs seized in the cylinder heads of some of our Overland Park area customers' vehicles with as little as 60,000 miles on them. The removal of these seized plugs can result in hours of labor by our technicians at Certified Transmission. There have been rare occasions when Certified Transmission has needed to remove cylinder heads just to get the spark plugs removed. Certified Transmission suggests that in order for our customers in the Overland Park are to maintain peak performance for their vehicles, that their spark plugs should not be run longer than 30,000 miles. Certified Transmission suggest that consumers should take those 100,000 mile spark plug marketing claims of manufacturers with a grain of salt.