Replace Spark Plugs Based on Time, not Mileage?

[SubLGT]

The FSM for my Subaru specifies that the NGK iridium plugs be changed at 60,000 miles, or 60 months, whichever comes first. I can see the logic behind having a time limit on parts such as rubber belts and hoses, but I don't see spark plugs being subject to large aging effects. I have 37,000 miles on my iridium plugs, and around 84 months. I am not inclined to change them just because I have over 60 months on them.

Any good reason I should go ahead and change them anyway?

 

[SuperDave456]

Nope, 100,000 miles is easy on most iridium plugs. Unless something else is going on just leave them in there.

 

[barkingspider]

I would leave them in there. Change at 100k if they are still firing normal at that time. The factory AC delcos in my s10 were replaced at 100k miles but it took over 12 years to get to that 100k. The plugs looked normal when I removed them.

 

[SubLGT]

Why 100,000 miles? Subaru specs 60,000 miles for my turbo motor.

 

[abycat]

my car says 100000km but I will do them at 80,000 just because I don't want any problems with them being stuck.

 

[volodymyr]

I once owned a Toyota Celica ST182 (1991 year) which I bought from one old man.

One of the first things I did after purchase was to change oil, filter and spark plugs. The car had 196'000 km (121'789 miles) and according to owner it was serviced on time in official Toyota garage.

During the spark plug change it looks like one plug cracked when I was trying to pull it up. It was a ruined evening for me because the plug ceramics cracked into several pieces and some of them were about to enter the cylinder. I took something like a sushi holders to pick up every individual piece of ceramics and made sure none of the pieces enter the cylinder. I guess I was lucky since none of the pieces entered the engine and car was running perfectly after the change.

I don't think the old plugs were iridium or platinum, however after this experience I try to change the spark plugs slightly before the recommended interval which is written in the manual.

 

[The_Jeff]

It's possible that at the time the car was certified the EPA required "hands off" until 60/60 and Subaru would have preferred something a little more often. Or, simply, subaru marketing figuring 60 months of city driving is more revs/ more sparks than 60k of highway drives.

This is the same phenomenon that brought us platinum long life plugs to begin with, and the indication that spark plug changes are a warranty item in California, "not necessary" etc verbiage in the manual.

 

[RISUPERCREWMAN]

I'd leave em in for 100K miles at least?

 

[MuzzleFlash40]

Single platinum plugs nowadays can go 100k, so iridium plugs can go that easy. That being said I would still change them out at 100k regardless.

 

[Rolla07]

Originally Posted By: abycat
my car says 100000km but I will do them at 80,000 just because I don't want any problems with them being stuck.


Dont bother..did mine at 180k kms and didnt even need to...they werent close to stuck and were still fine.

 

[volodymyr]

Originally Posted By: Rolla07
Originally Posted By: abycat
my car says 100000km but I will do them at 80,000 just because I don't want any problems with them being stuck.


Dont bother..did mine at 180k kms and didnt even need to...they werent close to stuck and were still fine.


Statistically speaking yours and mine examples are making 50/50 chances that plugs will either stuck/crack or will be fine

 

[tommygunn]

Just change them when you replace the head gaskets, which is why the spark plug change interval seems low for iridium

 

[skyactiv]

Originally Posted By: tommygunn
Just change them when you replace the head gaskets, which is why the spark plug change interval seems low for iridium

Impreza WRX and Legacy Turbo Subaru's actually have reliable head gaskets unlike the older naturally aspirated 2.5's.

I owned a WRX I bought new and put over 135K before selling it recently.

I changed my plugs at 62K for the first time. The plugs looked good, but I had galvanic corrosion to clean up.

 

[901Memphis]

Unless they are really easy to get to leave them until the mileage mark or you have a code. I've seen plenty of people run spark plugs further than rated without codes or any issue.

I was just talking with a coworker who has almost 200k on the oem probably 2006 ish Corolla and suggesting to him how it would be a cheap preventative maintenance job even though he has no issues.

 

[hattaresguy]

Steel plugs can seize in aluminum heads, hence the time limit.

If your cheap you can do what my buddy does and pull and never seize them every 3-4 years.

 

[01rangerxl]

Originally Posted By: abycat
my car says 100000km but I will do them at 80,000 just because I don't want any problems with them being stuck.


This might be their reasoning, though if it is, it's amazing to see an OEM care about ease of service.

Whatever their reason, that seems like a very short interval for iridium plugs.

 

[UNC164]

Iridium plugs can go 100k miles easy. Time should have no bearing other then possibly long time installed plugs starting to "stick" and being difficult to uninstall.

 

[simple_gifts]

I changed the plugs on my B2300 @ about 80 something K.

I get nervous about the difficulty in removing them if they had been in there 10, 11, 15 years....

 

[Merkava_4]

At 37,000 miles, you might want to adjust the gap and then put them back in there until 60K.

 

[901Memphis]

Just got my facts straight on my Co worker with oem plugs, it's a 2003 Corolla with 170k and it just threw and rod. Reason unknown at this point. I might buy it and drop another engine in it.