Worse MPG with Denso Iridium 5304
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From: East coast
2011 E550 4matic
Worse MPG with Denso Iridium 5304
A few weeks ago I made a 1,000 mile trip with the stock plugs in my '04 C230. Then a few days ago I changed them out to Denso Iridiums the 5304 package and did not re-gap (as recommended) and made the same trip again. Before the change I was getting about 30-32 mpg per fill up. With the Densos I got 26-28. The car seemed smoother but acceleration seemed worse. Anyway I'm going back to factory plugs. I was expecting a lot better. 
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From: Sacramento/San Gabriel/Riverside
01' C32o
there's your problem, most likely. you should regap it, although sparkplugs shouldn't have that much of an effect on your gas mileage. i think it would be less than a 1mpg difference
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From: East coast
2011 E550 4matic
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From: East coast
2011 E550 4matic
One thing I noticed besides the gap being bigger, is the length of thread on the Denso that screws into the engine is significantly shorter than the OEM plug, maybe that has something to do with it.
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From: Diamond Bar, CA
W206 PHEV AMG
the question is did you buy the IK20 for the 1.8 or the 2.3. plug # and stock # are the same, but they have different gap. 1.8 has .040 and 2.3 has .044. if you are seeing significant bigger gap than stock plugs then you probably bought the wrong plugs.
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2011 E550 4matic
Here is a cut and paste from Denso's site:
MERCEDES-BENZ
C230
YEAR 2004
ENGINE TYPE L4
LITER 1.8
CC 1796
ENGINE DESIGNATION
STANDARD PLUG NO -
STANDARD PLUG STOCKNUMBER -
PLATINUM PLUG NO -
PLATINUM PLUG STOCKNUMBER -
IRIDIUM LONG-LIFE PLUG NO -
IRIDIUM LONG-LIFE PLUG STOCKNUMBER -
IRIDIUM POWER PLUG NO IK20
IRIDIUM POWER PLUG STOCKNUMBER 5304
GAP 0.040
I don't see any other designation other than IK20 and 5304 to be able to tell what gap the plugs would come with.
Last edited by dan46n2; Feb 3, 2009 at 07:48 PM.
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'17 Jaguar XF
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might be wrong, but i remember seeing the gap on the package when i got the IK22 for the 32.
also on the site you can see Denso listed Ik20 also for the 2.3, but under the gap it's listed larger.
also on the site you can see Denso listed Ik20 also for the 2.3, but under the gap it's listed larger.
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2011 E550 4matic
Well I'm going to replace them for now with some NGK iridiums that I have on hand and see if I get better MPG until I go back to stock. Also I'll measure the gap on the Denso's and report back what they are since I can't tell from the packaging.
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No offense, but WTF are you doing? Swapping plugs until you can match the stock performance? Go back to the originals before you do some real damage, they're probably still good.
Last edited by mleskovar; Feb 4, 2009 at 12:47 AM.
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2011 E550 4matic
No, they're not, they have 60k+ miles on them and after taking them out they don't look that great. Also I already have the Denso and NGK plugs and a lot of free time.
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2011 E550 4matic
They looked fouled, I don't know what the gap is yet on the Denso plugs, I should get to them tomorrow. Also what did you mean by "real damage" in your previous post?
Last edited by dan46n2; Feb 4, 2009 at 12:55 AM.
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
Guys, running .04 different plug gap with a modern high energy ignition system won't make any difference to MPG, but running a plug with the wrong reach & heat range most certainly will.
So - check heat range
Check tip protrusion
Check thread length
If they are not the same as the Bosch OE plug in most parts of the world then don't use them.
And the comment "don't look great". Well - to read a plug with any accuracy at all it needs to have been running fully warmed up in the self cleaning range for about 15 miles, preferably longer, before what you are looking at means anything. If you took the plug out after a short run to the store, any plug will look crap.
So - check heat range
Check tip protrusion
Check thread length
If they are not the same as the Bosch OE plug in most parts of the world then don't use them.
And the comment "don't look great". Well - to read a plug with any accuracy at all it needs to have been running fully warmed up in the self cleaning range for about 15 miles, preferably longer, before what you are looking at means anything. If you took the plug out after a short run to the store, any plug will look crap.
Last edited by Glyn M Ruck; Feb 4, 2009 at 07:01 AM.
Thread Starter
Junior Member
Joined: Jan 2007
Posts: 43
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From: East coast
2011 E550 4matic
Guys, running .04 different plug gap with a modern high energy ignition system won't make any difference to MPG, but running a plug with the wrong reach & heat range most certainly will.
So - check heat range
Check tip protrusion
Check thread length
If they are not the same as the Bosch OE plug in most parts of the world then don't use them.
And the comment "don't look great". Well - to read a plug with any accuracy at all it needs to have been running fully warmed up in the self cleaning range for about 15 miles, preferably longer, before what you are looking at means anything. If you took the plug out after a short run to the store, any plug will look crap.
So - check heat range
Check tip protrusion
Check thread length
If they are not the same as the Bosch OE plug in most parts of the world then don't use them.
And the comment "don't look great". Well - to read a plug with any accuracy at all it needs to have been running fully warmed up in the self cleaning range for about 15 miles, preferably longer, before what you are looking at means anything. If you took the plug out after a short run to the store, any plug will look crap.
Thread length is definitely shorter on the Denso plugs, and I did run the car about 10-15 miles before taking the old ones out. I think I'll take your advice and go back to Bosch.
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From: MD
2007 C230 and 1985 Monte SS
If the threads are shorter, the electrode isnt in the right position in the chamber. It is possible that it is actually still in the spark plug bore when you tighten it down, which would cause a TON of shielding of the flame upon ignition, and that would definately cause your mpg decrease, as well as the loss of acceleration. Its not the irridium plug, persay, that is the problem, its the dimensions.
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
+1 - spot on & thank you. You also don't want shorter threads because the threads in the head will foul. Then someone will put the correct plug in again & bugger up the threads in the head. A good old VW problem.
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'17 Jaguar XF
Super Moderator
Joined: Jun 2008
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
At least for you it's only 4 plugs & not 12 like mine. I'm just staying with Bosch as well.
Last edited by Glyn M Ruck; Feb 4, 2009 at 03:56 PM.
