Replace plugs by mileage or wait for failure?

[Gebo]

Originally Posted by Snagglefoot
After blowing the plug well with a jet of air, I give it a shot of Liquid Wrench. I then give it a bit of torque to unseat it ( sometimes with a loud squeak). I then let it sit for 10 minutes to let the penetrant contact the threads. Then I unscrew it the rest of the way.


Just read after my posting +1

 

[Lubener]

Miles. An eventual misfire is not good for the CAT. Wide gaps from worn plugs are hard on the coils too..

 

[zzyzzx]

Originally Posted by HangFire
I would pull one from each car and take a look at them, check the condition, compare the gap to factory, post the results here and let the experts guestimate the age of them.


I was going to suggest this! Take it one step further and post pics of the plugs here and let us take a look at them,

 

[slo town]

OP:

Plugs from our 2011 BMW E90 328i. Plugs were original and had 67K miles on them.

Replace your plugs.

Scott

 

[zzyzzx]

Originally Posted by Snagglefoot
Iridiums with 180,000 miles on the left. New AC Delco Iridiums on the right.


I would probably regap the one on the left and reinstall it, unless it was giving me an issue. Depending on the car and how hard they are to replace and stuff too.

 

[StevieC]

I'd look at the plugs from the cylinders you can access (if possible) and make a judgement call based on that. Failing that follow OE advice at the very least. Running plugs too long can stress coils/coil-packs if the spark gap is too wide in some cases and cost you more down the road because of this added stress on the coils/coil-packs. Plugs are cheap, although the replacement might not be the easiest job depending on the vehicle and engine orientation. Like my Santa Fe and current Penta Star where the plenum has to come off to do the plug change.

 

[CT8]

Electricity takes the path of least resistance .

 

[anndel]

Go with miles. You don't want it to fail and cause damage downstream.

 

[joekingcorvette]

If your plugs have the long barrels like many engines have lubricate the barrels of the plug with anti seize compound but you don't need to use it on the threads. I did this on my 5.4 Ford F-150 engine. It is a must do to keep them from freezing in the heads.

 

[Anduril]

Whenever I buy a used car, the first things I do are replace the spark plugs with Iridium (that way I will likely never have to deal with them again) and change all the fluids.

 

[pezzy669]

Only thing I can say is my Mercedes experience is they go from just fine to horrific cold start misfires almost overnight. My '09 C300 went from starting just fine to a 5 of the 6 cylinders misfire CEL over the course of ~2"weeks, thought I could stretch it to the next oil change but no dice. Coil on plug you don't get much warning as the coils can pick up slack to a certain point.