I would replace them at 75,000 miles. It's recommended that you change them every 30, 000..
60,000 miles.
60,000 miles
How many miles should I have before I change my spark plugs
30,000 miles is recommended for spark plug replacement on all Chrysler/Jeep vehicles, not just the Jeep Liberty. Not only are plugs recommended at 30,000 miles, shock absorbers are recommended as well. As a mechanic for the Chrysler/Jeep Corp., i can say with confidence that it is not entirely necessary to change plugs and shocks at the 30k mile mark. Basically, "If it ain't broke, don't fix it!" (however, i do recommend at least checking the plugs at 30,000 miles)
If you have no spark on the 1991 Subaru Legacy, you should check the spark plugs and spark plug wires for replacement. You should also check the battery and ignition for replacement.
The maintenance interval is every 60,000 miles.
A suitable replacement for the XC92YC spark plug is the NGK TR55 or the Autolite 3923 spark plug. Both options offer similar performance and compatibility for engines that require the XC92YC. Always ensure to check the specifications and compatibility with your specific engine model before making a replacement.
They should not need changing until 90,000 miles.
For the US model Ford Focus (2006), spark plugs are the only thing to replace. There are no spark plug wires. Ford recommends spark plug replacement at 100k miles.
On a 2003 Jeep Liberty, the spark plugs are located in the engine cylinder head. For the 3.7L V6 engine, you'll find the spark plugs on each side of the engine, accessible from the top. You may need to remove any plastic engine covers to reach them easily. Make sure to use the appropriate tools and follow the manufacturer's guidelines for replacement.
30,000 to 45,000 miles
It is moderately easy to change the spark plugs on a Liberty, although it is rather tricky because of the gap between the spark plugs.