Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

When to replace spark plugs

I have a 2003 Mercedes Benz E320 with 50,000 miles that runs great that I have maintained well. In last visit to the dealer that suggest replacing spark plug - the stand is 1000,000 miles or 5 years. with only 50,000 miles and the running OK should I replace them?

What does the maintenance schedule that came with the car say?

I don’t think there’s a “standard” replacement interval applicable to all cars. For instance, my cars require new spark plugs every 30,000 miles. Other vehicles have recommended replacement intervals of 100,000, as you said. They’re not all the same.

Wow, one million miles? That is pretty high. I’m betting you wanted to say 100,000 miles? My response to your question is that you cannot do any harm by replacing the plugs early. You might also be preventing them from freezing up to your heads if you changed them now vs waiting until 100K miles, which will cause more head ache and expense. If your car runs well now, and you change your plugs, you probably won’t see any increase in performance or driveability. If you have the $$ and time now to get them replaced, it’s not a bad idea. It’s not necessarily wasting money, as some might claim.


Although the irridum tips of the plugs will survive 100,000 miles without performance-deteriorating erosion, plugs left in too long have been known to marry themselves to the heads. I’d replace them.

You can count this as one more vote for changing the plugs in the near future.

Personally, I will not leave spark plugs in place for more than 60k, simply because of possible damage to the heads if the plugs “seize” in place, which has been known to happen.

Trust me–the cost of new plugs is far cheaper than the repairs that might be necessitated if the plugs are left in place for as long as some car manufacturers recommend.

Thanks to all the contributors - there is a clear consensus - replacde those plugs.

I would replace them and in the future have them removed and inspected every 30-36K miles, so they don’t get stuck.