Get in touch with Bosch and ask them. I called several plug manufactures and asked questions. In my case the Autolite tech guy was the easiest and most helpful to talk to. Some of the others weren't as pleasant or as helpful.

 

For what its worth, I used Bosch 4418 +4s in my 2003 4.7 Dakota. I changed them out at 60,000 miles because I just don't believe in leaving any plug in much longer. They performed flawlessly and I have a feeling they could've gone further.

Then again, so did the factory Champions which I changed out at 30,000 miles.

But, a friend of mine did not like them in his 5.4 Ford.

Regards,
Dusty

 

Since I had read a few reports of people taking there Hemis beyond the recommended spark plug change interval without any loss in gas mileage on factory plugs, I thought I'd pass along my most recent results.

NGK now offers a direct replacement Laser Platinum plug for the stock SPLZFR5C11 used by Chrysler. It is the only plug designed to the factory heat range specifications of the original NGK copper core version. However, I elected to replace mine with the original type from Chrysler (Mopar #598051) because the new PLZFR5B13EG platinums are $13.00 a piece. The current plugs had 47,672 miles on them and the factory recommends them being changed every 30,000 miles. So I had gone over by 17,672 miles.

I was a little surprised at the results. First, I only detected two plugs that had grown in gap by 0.001 from the original gap that I set of 0.044 when I last installed them. The old plugs actually looked pretty darn good, especially when I compare them to other non-Mopar motors I've done work on recently. There was an ever so slight erosion of the center and end electrodes, but these looked like plugs that would've gone another 100,000 miles. The only thing I noticed was small medium tan streaks extending from the bases up the sides of the insulator, indicating that perhaps the internal seals were leaking. The factory specifies a 0.044 gap. For this plug change I did not re-gap the new plugs out-of-the-box. They came set at a consistent 0.040 and that's how I installed them. ( This is a new test, I guess.)

Before the plug change I would've said this engine was running flawlessly, but as soon as I had driven the first mile I could feel a slight improvement in acceleration and smoother shifts. Apparently I had not noticed before the plug change that the 4 to 8 and 8 to 4 cylinder transition was a little coarse, because now the transition is completely imperceptible. Full throttle punches seem improved, too.

Starting has not been affected (no improvement), however idle has improved ever so slightly. In fact I cannot detect any motor imbalance at idle at all and it appears to be idling down about 100 rpm less than it was.

As for gas mileage, before I changed the plugs the EVIC was indicating 15.1 mpg in the driveway, but it's really is too soon to tell. In 170 miles it has gone up to 17.2, numbers I haven't seen since late December. This is admittedly inconclusive. The weather has changed since my last fill up (now warmer by 10 or so degrees) and the last 170 miles were not exactly my normal driving cycle. However, while strictly a sensory perception, the engine feels more responsive, and according to the MPG databar I can travel on similar roads and see a higher number.

Others report different results, but I suspect some think their Hemis are running at optimum when they actually aren't because these motors run so well even slightly out-of-tune. This test indicates to me a plug change did make a difference. I don't think I'll try to go as far on plugs as I did this time.

As to the difference in metals issue, I think copper core plugs generally offer better reliability over term, assuming they meet the manufacturer's heat range specification. The problem there is most cross referenced plugs do not.

Some say that the increased electrical resistance characteristics of platinum or iridium cause problems. I'm not convinced of that. Electrical current (speed of electron flow) is only impacted by conductor resistance in a complete circuit. The secondary circuit in a spark coil system is never complete (i.e.: there is a gap that a spark must jump). Since voltage (electrical pressure) is the factor that causes a spark to jump across a gap, it is the gap itself that determines the voltage necessary to produce an arc across the electrodes of the spark plug.

Even if one doesn't buy that theory, the extremely small increase in resistance of platinum or iridium conductors of less than 1 ohm in a resistor spark plug that already contains between 4000 - 10,000 ohms, is totally insignificant.

I suspect that the real culprit is differences in the heat range of the plug or the heat retention value of the electrode conductors themselves.

Best regards,
Dusty

2010 Ram Big Horn 1500 Quad Cab2WD, 5.7 Hemi, 545RFE, 3.92 LSD, factory dual exhaust, 20” wheels

 

my 09 , changed mine over to Platniums at 45, 000 , changes them with another set of plats, around 155,000 .... I ave on the clock now 181,000
very happy with the platniums

 

Which plugs?

 

Ive been running Denso Iridium plugs, i heat range colder, with a 180 tstat for over 50k on an 09 hemi..never an issue.......runs like a bastard.......