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04 Mercedes C230, 08 Rondo LX V6
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359 Posts
Discussion Starter #1
Over the last 2K miles I've averaged 20.9 mpg with a couple of very recent 17-18 mpg tanks. During the same period (and distance) last year I averaged 21.6 mpg. Driving style and patterns should be essentially identical. Buying same brands of Top Tier gasolines (mostly Shell and Phillips 76) as I have for the 50K miles I've owned the car. So the injectors, valves, and upper cylinders should be clean. Air filter replaced (for second time) at 56K miles. So, with 60K miles on the car, I'm wondering if spark plug replacement is indicated even though the manual says 100K miles (but "more frequently" if "severe conditions" driving). My 700 lb trailer towing is <10% of total miles, I do very little mountain driving, but lots of driving at temps well over 90F. Any thoughts, comments, or experiences to share? Thanks!
 

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2010 Subaru Impreza 2.5i Premium 5-door, *old* 2009 Kia Rondo LX 4cyl 2.4L
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492 Posts
I never believe "100K" spark plug recommendations. I changed mine out to some new iridium tip plugs around 55K. I'm still getting around 19-20mpg, but I'm also doing short, city trips only.
 

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Good spark plugs are so crucial for proper engine operation and are reasonably inexpensive to change out. 30,000 miles out of one set of plugs would be recommended, 45,000 would probably be stretching it.
 

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04 Mercedes C230, 08 Rondo LX V6
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359 Posts
Discussion Starter #4
$350-400 to replace plugs!! Apparently it is necessary to remove the surge tank (intake plenum) to get at the rear three plugs. I found a 16 step (!!!) procedure online for doing so. Once the plenum is removed, is access to the plugs easy? Has anyone on the list done this job?
 

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2016 FIAT 500X Trekking Plus AWD; 2016 Kia Forte5 SX 1.6T A/T
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6,807 Posts
I checked mine at 42k miles and they were OK.
However, I would not wait till 100k miles... insane. As the core may be still intact, the insulator takes the beat/heat ;).
 

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04 Mercedes C230, 08 Rondo LX V6
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359 Posts
Discussion Starter #6
Do you view this as a DIY job? Intake manifold must be removed to get at rear plugs.
 
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