Spark Plug Replacement Intervals - Why?

[Jetronic]

Again - I see no drop in mileage. This would obviously be the first indication of electrode burn-back, and it doesn’t seem to be happening.

I have a degree in mechanical engineering. I get that things wear out - but I also know that they give indications that they’re wearing out. I don’t accept replacing a widget that’s still fully functional just because somebody put a replacement interval in a manual.

I would prefer to replace them at a convenient time for me, and not find out they're no good half way up the Brenner pass. I'd at least check the plugs around interval time.

 

[Patman]

I have 176,000 miles on my Civic and it’s still got the original plugs. Engine runs smoothly and still gets over 60 MPG on a lot of my drives so I’m pretty confident that they are still doing their job perfectly. At this point they might already be difficult to remove so I might as well just keep going! I recently talked with another 2.0 Civic owner who has 250k on his plugs and they are still going strong. Honda uses NGK laser iridium plugs

 

[i6pwr]

I didn’t come here to argue, I came here to get a reason besides “the manual says so”.

Okay, so the coils will run hotter - is that necessarily going to kill them sooner? Will it manifest itself in some other way than a drop in fuel economy? Is there some other indication of worn plugs that is readily apparent?

Because it's preventive maintenance.

It's cheaper to replace 4 plugs at 80K-100K than to also wear your coil packs from increased load to jump the larger gap.

You might not see a drop now, but are you recreating the exact conditions? Ambient temps, warm up time, idle time, traffic, making the same green lights in traffic, etc.

Why risk it? Keep your engine operating as efficiently as possible. I replace my plugs and upstream sensor(s) at 80-100K to maintain peak efficiency.

Plugs wear out, just like tires, brakes, belts, etc.

 

[Egg_Head]

I didn’t come here to argue, I came here to get a reason besides “the manual says so”.

Okay, so the coils will run hotter - is that necessarily going to kill them sooner? Will it manifest itself in some other way than a drop in fuel economy? Is there some other indication of worn plugs that is readily apparent?

How long do you run your engine oil in this vehicle before changing?

 

[dnewton3]

Folks -
The discussion is fine. The taunts are not.
Be careful or the thread gets locked.

 

[kam327]

A pertinent fact that's missing from this thread is that Mazda calls for a spark plug change at 40,000 miles for its 2.5L turbo engine, compared to a much more reasonable 75,000 miles for the non-turbo version of the same engine. So the OP's question seems even more important since 40,000 miles seems an absurdly small interval for a spark plug change. I've been wondering this myself since I have a Mazda6 turbo with 37,000 miles.

 

[Glenda W.]

I’ve seen some engines run well on some severely worn plugs. My only concern is when the plug can no longer be removed without damaging the threads in the cylinder head. A simple job turns into a nightmare very quickly.