I have 2005 C320 3.2 V6 with 12 plugs . Car is at 68K miles now.

According to the owner manual plugs should be changed at 100K miles and as far as I know car came with Bosch FR8DPP33 double platinum plugs?

Can they really last 100K without decrease in performance?

At what interval have you guys been changing them and what was the condition of the oem plugs?

 

Changed mine at 100K miles and they looked like they could have gone another 100K with no problem. Gap was still perfect even after all those miles. No change in performance with the new plugs, but it was running great before anyway. As long as you stay away from leaded gas there's nothing to damage the plugs.

 

i think they MUST last that much

 

Gee, I would never think of letting it go that long...
I figure 50-60K miles....I thought I saw pics around here of 100K plugs
and they were shot? Maybe it depends on the engine.

 

I don't know how it was on 2005 cars, but on today's Mercedes they say 5 years. I'm going to go ahead and replace them at 5 years.

 

The m112 uses a twin spark per cylinder setup, which fire sequentially; one after the other. Because of this, the plugs can go on much longer than traditional 4 valve engines of todays. Only reason you should change them out early is because of rough idle, misfires, or the gap is starting to increase (if you have a gap, you need to change the coils too).

 

I guess 5 year time is to take into account all the heat cool cycling which does put wear on the plugs...so I should be good till sometime in 2010...

1000 mile road trip next week will be a good way to check hwy consumption. if it matches OEM ratings I will leave them alone.

What have you guys been getting on hwy with this model?

 

with my 01 c320 i can get 30-32mpg on hwy trips. (speeds below 80) cruise set on like 75.

 

Same for me. 90+ mph gets me about 28 mpg.

 

you guys have 4matic right?

 

I'm pretty sure Trey's car is not 4Matic. Is your car?

My owner's manual says 5 years for my 2005.

 

You asking me?In 01 or 02 they did not have 4matic
if you have a 4matic i would say take off 2mpg let some people with 4matics chime in because i honestly don't know what they get.

as for the spark plugs i would do it sooner then later. on my car when i did it i did not notice a difference at like 110,000. the former owner and i as far as i can tell did like 90% hwy driving so that is probably why.

 

I changed my spark plugs after 28k miles (5 year old plugs). The gaps were still nearly perfect, but I did notice a pretty big improvement in low-end power. I think this is probably because I drive mostly short trips so the plugs may have been a bit fouled.

 

I have an 02 CL600 with about 105k miles on it. I've gone through 3 sets of spark plugs. I've tried different spark plugs (Bosch +4 and such) but at the end of the day, the conclusion I've come to is that I should stick to stock oem spark plugs. They might not give you the little bit of extra power, but in the long run, they're more appropriate for the vehicle.

If someone is really looking around for some serious plugs, check out Halo. My master mb tech is crazy about them, but they aren't made for all Benzes. Unfortunately, they don't make them for my car.

 

Sorry for this Necro-bump. But I am encouraged by this post.

My 2001 C320 has 128,000 miles, on its original plugs. The car runs great, no stumbles or knocks, etc.

I am reluctant to change the plugs, because at nearly 20 years, I suspect I will have lots of problems with dry-rotted wiring and coils that will dwarf the expense of changing just the 12 plugs. Given the value of the car at this age ($1000 or less), my temptation is to continue driving it until I start to get issues, then sell it for junk.

What do you say?

 

The plugs last pretty much forever. The ignition coils however will start failing. Not sure about your specific model (V6) but the coils started going at around 200k km for me.

I had my plugs changed out at 180k and other than a bit discolouration they still looked great. No problems with pitting or gaps. Thinking of going way farther (another 300k?) with my current set.

The wiring on these cars aren't known for dry rotting at all. Haven't experienced this personally anywhere on the car, or read anything about it on this forum.

 

I agree with Slammer. Coils go first and if the engine isn't missing the coils are OK. I read somewhere that the real reason to change plugs now is so they won't get stuck in the block. As long as the motor is running fine at this point in its' life leave it alone. "If it ain't broke don'' fix it." I also agree that messing with old wiring is asking for trouble. A couple of those plugs .... up against the firewall ... are a real ***** to change. Actually with all the plugs in that engine are hard to remove the high tension lead if I remember correctly.

 

one big reason to change the plugs is that if you leave them in way to long it may be difficult to remove. Steel thread plugs in an aluminium cylinder head... despite anti seize coatings you are asking for trouble. Even now, ease them out slowly with finesse... half turn out.. quarter turn in.. half turn out .. etc..

 

Very good advise.
Just changed plugs on me lady's ML350 and did exactly as you described.. Plugs were sticky for sure at 50K miles since they were
supposedly changed by mechanic, but no anti seize on the plugs and no dielectric grease on the
coil connections. Tsk tsk! I said a Hail Mary before each plug and liberally sprayed some liquid wrench while doing as you describe
back and forth to work it in to the threads. Thankfully all went well, and running perfect now,
with the addition of a new Coil pack as well. Plus both batteries, and oil change and new air filters.
Running very sweet.
Also I find as the plugs age it stresses the coilpacks and you get misfires. No fun running on 3 or 5 cylinders depending on the engine.