new spark plugs every 2yrs or 32K miles? why?
11-27-11, 04:11 PM
#16
Lexus Fanatic
Modern spark plugs, BTW, should not foul as long as you use the factory-recommended (or equivalent) ones of the proper heat-range, the ignition system is working properly, the rings or valve-seals are not worn to the point where oil is getting into the cylinders, you dump in some BG-44K or equivalent fuel-system cleaner every few years, and use a decent-grade unleaded gas with a good detergent-additives (I usually recommend either Chevron or Shell). Doing this should reduce the chances of fouling to almost zero.....although Josh ponted out that some Chrysler engine designs can contribute to it.
Last edited by mmarshall; 11-27-11 at 04:15 PM.
11-28-11, 09:38 AM
#17
Couple things wrong in this thread...
1st - Dodges with the Hemi's have two spark plugs per cylinder because that is the easiest way to do single coil on plug AND fire a wasted spark... Some cars do this by making one coil per two cylinders and it just fires twice as often - Dodges do this on the Hemi's so that the coil doesn't have to fire as often, but they still get the advantage of wasted spark, which lowers emissions and burns anything left in the combustion chamber after the initial ignition event...
2nd - almost all Dodges have terrible maintenance schedules, including spark plugs, rear differentials and more... I'd give you specifics, but not at work right now... Will the parts last longer than recommended, sure, probably, but they are giving what they expect to prevent the average consumer from ever having drivability issues...
3rd - the reason manufacturers have almost all gone to iridium or platinum plugs has nothing to do with how the engine is laid out, it has everything to do with reduced maintenance costs in general... Think how much more appealing it is when a new car buyer goes and sees that the first major scheduled maintenance for their car is 100k miles... On top of the prospective buyer not having the maintenance intervals to contend with, there is also buyer satisfaction in the long run as well... Just think, driving your still new car with only 35k miles on it, not realizing you should have changed your spark plugs at 30k, starts to misfire, take it back to the dealer only for them to say "well, you missed your maintenance." Customer is not happy, whereas the neighbor is comfortably driving their car at 80k miles and still no issues...
4th - There is a proper procedure for removing high mileage spark plugs that are having issues coming out cleanly... Most of the problems regarding these really have nothing to do with the maintenance interval at all, instead poor engine design... For instance, the Ford Triton motors - in those, with the extended maintenance interval, many have problems removing the spark plugs due to carbon buildup... the reason behind this is that the spark plug threading protrudes too far into the combustion chamber - the carbon builds up around the threads and becomes very hard, screwing up the threading in the head... there is a removal process even for this - with engine cold, back the spark plug out a quarter turn - fill the bottom of the plug well with carb cleaner, enough to cover the hex nut part of the spark plug - this will soak down into the cylinder and soften the deposit (wait minimum of 15 minutes)... then work the spark plug in and out until it comes out...
1st - Dodges with the Hemi's have two spark plugs per cylinder because that is the easiest way to do single coil on plug AND fire a wasted spark... Some cars do this by making one coil per two cylinders and it just fires twice as often - Dodges do this on the Hemi's so that the coil doesn't have to fire as often, but they still get the advantage of wasted spark, which lowers emissions and burns anything left in the combustion chamber after the initial ignition event...
2nd - almost all Dodges have terrible maintenance schedules, including spark plugs, rear differentials and more... I'd give you specifics, but not at work right now... Will the parts last longer than recommended, sure, probably, but they are giving what they expect to prevent the average consumer from ever having drivability issues...
3rd - the reason manufacturers have almost all gone to iridium or platinum plugs has nothing to do with how the engine is laid out, it has everything to do with reduced maintenance costs in general... Think how much more appealing it is when a new car buyer goes and sees that the first major scheduled maintenance for their car is 100k miles... On top of the prospective buyer not having the maintenance intervals to contend with, there is also buyer satisfaction in the long run as well... Just think, driving your still new car with only 35k miles on it, not realizing you should have changed your spark plugs at 30k, starts to misfire, take it back to the dealer only for them to say "well, you missed your maintenance." Customer is not happy, whereas the neighbor is comfortably driving their car at 80k miles and still no issues...
4th - There is a proper procedure for removing high mileage spark plugs that are having issues coming out cleanly... Most of the problems regarding these really have nothing to do with the maintenance interval at all, instead poor engine design... For instance, the Ford Triton motors - in those, with the extended maintenance interval, many have problems removing the spark plugs due to carbon buildup... the reason behind this is that the spark plug threading protrudes too far into the combustion chamber - the carbon builds up around the threads and becomes very hard, screwing up the threading in the head... there is a removal process even for this - with engine cold, back the spark plug out a quarter turn - fill the bottom of the plug well with carb cleaner, enough to cover the hex nut part of the spark plug - this will soak down into the cylinder and soften the deposit (wait minimum of 15 minutes)... then work the spark plug in and out until it comes out...
11-28-11, 12:16 PM
#18
Lexus Champion
Thread Starter
Does the Jeep have a cylinder deactivation system, my brothers 08 300, 5.7 has regular 30k plugs but it has the MDS, were at certain speeds 2-4 cylinders shut down, we put platinum plugs in and within a short time the engine went into limp mode, switched back to regular copper 30k plugs and problem went away.
Have no idea why it needs specifically copper plugs but it does, the V6 300 and SRT8 models have 100k platinum plugs
Have no idea why it needs specifically copper plugs but it does, the V6 300 and SRT8 models have 100k platinum plugs
BTW -- thanks for all the input!
Great Info!
11-28-11, 07:23 PM
#20
Dysfunctional Veteran
They have dual plugs because the computers monitor the plug temperatures, especially when the MDS kicks in. Copper provides a hotter spark, and iridium can overheat, especially at highway speeds where they are firing much more often. 
The dishing of the hemispherical chambers also affects the plugs, since any fuel not burned naturally sits at the bottom of said sphere. With the hotter plugs, this problem is mostly alleviated.
The dishing of the hemispherical chambers also affects the plugs, since any fuel not burned naturally sits at the bottom of said sphere. With the hotter plugs, this problem is mostly alleviated.
I knew why the hemi's have it, why the 4.7L does was beyond me. But now its not. I never did understand the 2 plugs per cylinder thing and did not really think of the unburned fuel factor.
12-07-11, 02:21 AM
#21
Couple things wrong in this thread...
4th - There is a proper procedure for removing high mileage spark plugs that are having issues coming out cleanly... Most of the problems regarding these really have nothing to do with the maintenance interval at all, instead poor engine design... For instance, the Ford Triton motors - in those, with the extended maintenance interval, many have problems removing the spark plugs due to carbon buildup... the reason behind this is that the spark plug threading protrudes too far into the combustion chamber - the carbon builds up around the threads and becomes very hard, screwing up the threading in the head... there is a removal process even for this - with engine cold, back the spark plug out a quarter turn - fill the bottom of the plug well with carb cleaner, enough to cover the hex nut part of the spark plug - this will soak down into the cylinder and soften the deposit (wait minimum of 15 minutes)... then work the spark plug in and out until it comes out...
4th - There is a proper procedure for removing high mileage spark plugs that are having issues coming out cleanly... Most of the problems regarding these really have nothing to do with the maintenance interval at all, instead poor engine design... For instance, the Ford Triton motors - in those, with the extended maintenance interval, many have problems removing the spark plugs due to carbon buildup... the reason behind this is that the spark plug threading protrudes too far into the combustion chamber - the carbon builds up around the threads and becomes very hard, screwing up the threading in the head... there is a removal process even for this - with engine cold, back the spark plug out a quarter turn - fill the bottom of the plug well with carb cleaner, enough to cover the hex nut part of the spark plug - this will soak down into the cylinder and soften the deposit (wait minimum of 15 minutes)... then work the spark plug in and out until it comes out...
12-07-11, 06:11 AM
#22
if you follow my procedure, it shouldn't be an issue... we have a ex Ford master tech working at our shop and we were talking about this just the other day - he said he's only had a couple (out of hundreds) that ended up breaking or jamming up threads once he started following this procedure...
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