Re-use barely used spark plugs or buy new ones?

[JEDI]

2005 Mazda3i 2.0L AT, 140k miles.

at 80k miles i bought new Iridium spark plugs from Adavanced Auto Parts. They dont sell OEM so i bought compatible Iridium spark plugs. it gave worse gas milage.

after 10k miles on those, i went on Ebay and bought OEM.
same gas milage as the ones at Advanced auto.

after 10k miles on those (now 100k total), i went back to the spark plugs that came w/the car when i bought it at 5miles on the odometer.

now i'm at 140k miles which means i've been w/the original spark plugs for 120k miles.

1) when should I change to new ones?
if never until problems, then what are the warning signs?

2) if change to other spark plugs, do i go back to one of the sets i already own?
or buy a new set?
(ebay has the cheapest price for the OEM ones.)

 

[T2urtle]

what much bad gas mileage as we talking here.

Generally i'm OCD with plugs that i can easily replace ( normally most 4 cylinder engines) that i do them when i have time.

I would ensure the ebay/oem with 10k are properly gapped and just run those.

Personally i've never seen an increase or decrease in MPG with spark plug changes on my vehicles. But i rarely wait till 105k (what most are recommending). I aim to do them at the old fashion 60k and try to get some type of platinum. UNLESS its one of those cars with the really hard to reach rear cylinders or a subaru.

 

[shabby]

They dont sell OEM so i bought compatible Iridium spark plugs. it gave worse gas milage.

Were they gapped properly?

 

[JEDI]

Were they gapped properly?

the gap distance looked the same as the originals.

so buy a gap tool and re-use the 10k oems?

 

[T2urtle]

Some people/places say you shouldn't gap them because you can damage the tip. I carefully gap mines no matter what because i've found a pack of NGK that were suppose to be gapped at .0XX to actually be .1xx, it gave me a random hard start/ no start for the 2k miles i put on them before i properly gapped.

You still didn't state how much MPG change it was, like what you start off with and have now. That 2.0L isn't known for GREAT MPG if i remember correctly.

 

[SpatiallyAware]

I remember your last thread about this..


Personally I would buy OEM equivalent NGKs brand new, from a local store.

Maybe one of the ones from ebay were defective or something, it seems like you tracked this VERY closely and were 100% confident that your mpg went down.

As others said, pre gapped doesn't mean they're perfect - and some of them can't be regapped. I would check for consistency more than actual gap. Make sure to not touch the electrode.

 

[EagleKeeper]

You never re-gaped the ones you purchased; that should explain the problem.

For a $2 you spent how much??

 

[jagec]

Iridium gapping information, straight from Denso:

Q. Do I need to set the gap?
A. Generally, no. The DENSO Iridium Power plug comes pre-set with a protective sleeve over the firing end, to protect the gap from accidental alteration. DENSO Iridium Power?s ultra-efficient firing power compensates for normally recommended gap settings that are smaller than the pre-set value. In the cases of vehicle modifications (nitrous, turbo-chargers, super-chargers, high power ignition systems, etc.), some adjustments may be desired. Or, if you prefer to remain consistent with factory specifications, you may adjust. However, please be careful not to place any stress on the fine center electrode during adjustment. You could accidentally break off the very hard, and therefore brittle, tip.

 

[JEDI]

Some people/places say you shouldn't gap them because you can damage the tip. I carefully gap mines no matter what because i've found a pack of NGK that were suppose to be gapped at .0XX to actually be .1xx, it gave me a random hard start/ no start for the 2k miles i put on them before i properly gapped.

You still didn't state how much MPG change it was, like what you start off with and have now. That 2.0L isn't known for GREAT MPG if i remember correctly.

mpg went down to 10%, from 32mpg to 29 mpg in 70% hwy/30% city driving when usuin other sparjk plugs.

and for some strange reason, this month (august), all 3 of my weekly fillups are at 33mpg!?
no change in driving destination or habits.

i guess i'll keep these original sparkplugs till i get a check engine light?

um.. how do you know when its time to change the spark plugs?

 

[Zap]

mpg went down to 10%, from 32mpg to 29 mpg in 70% hwy/30% city driving when usuin other sparjk plugs.

and for some strange reason, this month (august), all 3 of my weekly fillups are at 33mpg!?
no change in driving destination or habits.

Maybe there was a change in the gasoline? It is really common in some areas for diesel formulations to change based on the season, causing huge swings in mileage. For gasoline, maybe the station switched to/from having alcohol?

 

[sdifox]

get new ones. The labour cost lots more than plugs, even if you sre doing it yourself.