How often are you supposed to change spark plugs and what are some signs that you need new ones?

I'd do it every 20,000 miles, you can tell when they are going by lack of power, hesitation and hard starting.How often are you supposed to change spark plugs and what are some signs that you need new ones?
Every car company gives a guide of when to change them in the service manual. I normaly change mine out with every tune up (about 25,000 miles). However I drive an older carburated vehicle. If you have a newer fuel injected vechile they can last much longer (50,000-100,000 miles) here is how you can look at them and tell

http://dodgeram.info/Engine-Gas/SparkPlugs/spkplghnbook.htmlHow often are you supposed to change spark plugs and what are some signs that you need new ones?
This is the definition of a multi-faceted question! The factors involved in when to change your plugs are many.



If you run 87 octane gas and drive your car like you really mean it I'd recommend every 40,000 miles. If you go easy and spend most of your time on the highway then 80-100k should be fine.



The symptoms of when the plugs are going ';bad'; can vary as well. If you're losing a great deal of power, especially at higher speeds you can be fairly certain the plugs needs to be changed (this is assuming all other aspects of the vehicle have been maintained). If you're at a stop light with the vehicle in gear and you can feel it vibrate or ';miss'; through the steering wheel chances are a plug is fouled, clogged, or weak.



When changing the plugs be certain to inspect the old ones, look for oil on the plugs or a heavy white residue...this indicates the engine has other issues in it's near future. Also, do not fall prey to the fancy spark plugs you see on TV or in other forms of advertisement. Stick with the OEM plug (i.e. AC Delco for GM) or NGK. The fancy 4 and 2 prong plugs are a marketing ploy that will generate no additional performance and can very easily foul up your electrical system/timing/gas mileage.
Usually you can tell when the vehicle idles rough. If your vehicle has 100,000 miles or more go ahead and change them. It wouldnt hurt either if you change them now as they are cheap and usually easy to replace yourself.
Your owner's manual tells you when to change the spark plugs. My 2000 Taurus are due for a change at about 100,000 miles because they are the Motorcraft platinum plugs. I have 80,000 miles on them now and the car truly runs like a rocket ship. I love it!
I change mine around 25K to 30K miles.You can tell because the old dog want get up and go like it use to.

Some times you will grind and grind and it just want dust off.If you check your gas mileage it will be way off.Check your tires and keep the right amount of air in them,this will help,also the air filter,good luck
You should change them at least once a year. It's like spring cleaning for your motor.
some car makers say 100,000 miles but if u wait that lonmg they becone ';welded'; to the aluminum head and break off during removial...i go 50 to 75 thou...and do the wires too...
it depends on what kind of plugs you have. some plugs wear longer then others.you can check them,and if the firing tip is worn clean down to the porcelant or all carboned up,then i would say change them,but sometimes,if they still look pretty good,take a wire brush and clean and reguage them.