My '12 has consistently gotten 15.x miles per gallon. One tank was upper 14's but the rest all fall in the 15's. This is with winter blend gasoline. I am curious how the summer blends will do when the time comes.

2012 quad cab
5.7
4x4
3.92 gears

 

09 cc 4x4 hemi big horn 90k
Magnaflow muffler, K&N drop in filter
285/60/20 Goodyear duratrec
3.55
Miles divided by gallons. Calculator
13.6mpg all day
Warm up 5 minutes before 6 mile drive to work at 55mph
Short trips to and from store 6 miles away as well going 45-55

 

My apologies in advance if this post seems a little out-of-place in this thread, but 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, I thought I'd pass along my most recent results.

Although NGK now offers a direct replacement Laser Platinum plug for the stock SPLZFR5C11 used by Chrysler, I elected to replace mine with the original type from Chrysler (Mopar #598051) because the 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.

(After I finished replacing the plugs i forgot how punishing this process is to the human body. A guy my age ought to start paying somebody else to do this, but I'm stubborn. That $13 price tag for the Laser Platinums didn't sound so bad by the time I got to the rear cylinders!!!)

I was a little surprised. 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 good, especially when I compare them to other motors I've done work on recently. There is a slight detectable erosion of the center and end electrodes, but these looked like plugs that would go 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. I did not re-gap these plugs. They came set at a consistent 0.040 and that's how I installed them.

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 much improved.


The idle has improved as well. In fact I cannot detect any motor imbalance at idle 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. Now it really is too soon to tell, but in 94 miles it has gone up to 16.8. I have not seen a number in the high 16s since December. This is admittedly inconclusive. The weather has changed since my last fill up (now warmer by 10 degrees) and the last 94 miles were not my normal driving cycle. However, while strictly a sensory perception, the engine feels better and according to the MPG databar I can travel on similar roads and see a higher number.

Anyway, maybe others have had different results, but this test indicates to me a plug change probably does make a difference.

Best regards,
Dusty

2010 Ram Big Horn 1500 Quad Cab 2WD, 5.7 Hemi, 545RFE, 3.92 LSD, dual exhaust, 20” wheels

 

Dusty, actually I find your post very interesting. My 2012 5.7 has about 11,000 on it and a plug change recommended at 30,000 seems a little low, but I've always been a ford man and they say 100,000. Although I know the 5.4 very often can't go that long. Just looking at the Hemi I dread changing plugs but maybe it will be worth it around 30,000. I assume yours has 16 plugs? Darn, sounds like an all day job almost!!

 

Tunaman,

The newer 5.7 Hemis (2009 and up) do not have the plug wire cross over design common on the older engines. The newer design has one double coil over both plugs, eliminating the plug wire that crossed over to the other bank.

When you consider that the factory SPLZFR5C11 NGKs are nothing more than a standard, copper core plug, 30,000 miles is really in the ballpark for that type. The scheduled plug change on my daughter's old Hyundai was 30,000, and I just did a neighbor's Saturn a few months ago and that motor's schedule change was 32,000 miles.

The 100,000 mile plugs are usually a different design with a much higher cost. The NGK Iridiums for the F150 5.4 are around $13 a piece (my son-in-law has one). I paid $3.54 a piece for the regular plugs at my Dodge dealer.

To prevent advertising advantage and criticism by their competitors and scaring people, maybe Chrysler didn't want to use a $13 plug on an engine that requires sixteen of them.

I am able to accomplish changing plugs on my 2010 without air tools and using standard ratchet, extensions, swivel joint, and a magnetic 5/8 plug socket. But I have to literally lay across the grill and radiator support in order to work on all but the first two cylinders on the right bank. For a guy that's old and overweight it's tiring, if not a little painful. It's not an all day project. I think it took me a little over 3 hours, which includes answering the phone twice and four or five runs to the bathroom. I do take breathers after each of the toughest cylinders.

The plugs on the left bank, third cylinder is a real challenge because they are directly under the power brake booster and have the least amount of room over the valve cover. The last cylinder on the left bank actually has more room, but it's hard to see as you're reaching that area.

The last plugs (rear most) on the right bank is under the heater hoses. Getting the coil pack out requires a brutal twist to the long rubber plug boots. I disconnect the heater hoses from the two plastic clamps that run along side the cylinder head, plus the one on the firewall.

The whole process is a lot easier if you have two hands on one arm, and two elbows on the other.

Bests,
Dusty
2010 Ram Big Horn 1500 Quad Cab 2WD, 5.7 Hemi, 545RFE, 3.92 LSD, dual exhaust, 20” wheels

 

2012 Ram 1500 Hemi Big Horn
50% street,50% highway
20 inch factory tires.
all stock.
13.00 to 13.5 mpg
arround 300 miles with 23 galons in this combination.
arround 400 miles with 23 galons only highway with speeds over 75 mph.

 

Year: 12
Model: 1500 ST quad cab 4x4
Engine: 5.7 Hemi
Highway percent: 50
City Percent: 50
Location: MN
Octane: 87 or 89 (notice about 1 MPG better with 89)
Hand or Computer calc: Hand
Miles on truck: 13,000
MPG: 13-15 AVG
Mods: K&N drop in, 2.5' leveling kit, Air lift 1000 coil bags, glasspack exhaust, tonneau cover.

To elaborate more on this, If I drive only to work and back for a full tank (8 miles each way) with 7 stop signs/lights each direction which obviously kills economy, i average between 13 and 15 depending on the time of year. Keep in mind my truck is barely getting up to operating temp. before I get to work so it's less efficient. I recently took a trip from the cities to Duluth (240 miles round trip) set the cruise for 70 the whole way, stopped at taco bell and the casino so some idle time, only stepped on it a hand full of times because people don't know how to merge. Minor ups and down hills along the way with a 6% grade downhill going into Duluth ( and then went up that same hill coming back) this grade is about 2 miles. It was 32 degrees going up and 34 degrees coming back, no wind any direction above 5mph, i averaged 17.3mpg hand calculated on 89 octane. That is with 5w20 valvoline synthetic motor oil and 75w140 synthetic rear gear oil,K&N drop in air filter, glasspack, 2.5" leveling kit, rear coil bags, tonneau cover AND 285/70/17 Wrangler Duratracs set at 40psi with 95% tread. I'm willing to bet that on this same trip in the summer with warmer temps and more street savvy tires you could average 19 and more upwards of that if the vehicle is stock height and running full synthetics, also keeping in mind mine is 4x4. The highest i've seen out of mine so far was when I hand calculated it when I first got it on a 20 mile trip (which isn't that accurate for such a short distance) was just over 21, that was at 60mph, the fastest my truck will go while maintaining MDS about 90% of the time.

 

My Truck is a Year old already, time goes by so fast. I drive in city mostly. I have not wen ton a long trip yet, but my 04RAM got like 9-11 mpg same driving! So i am happy with what i am getting, the best thing to do is try NOT to jump on it! my area is mostly 45 mph on roads.

2012 DODGE RAM 1500 CREW CAB 4X4
BIG HORN EDITION
Engine: 5.7 Hemi
Wheels: 20
Highway percent: 20
City Percent: 80
Location: PA
Octane: 87
Miles on truck: 17,500
MPG: 14.5-15 AVG
Mods:Tonneau cover

 

Year: 10
Model: 1500 SLT crew cab 4x4
Engine: 5.7 Hemi
Highway percent: 50
City Percent: 50
Location: NM
Octane: 89
Hand or Computer calc: Computer
Miles on truck: 30,000
MPG: 15.6 AVG
Mods:None

 

I've been checking this thread for the couple of years it's been here - not bad for these Hemis! If you really want to feel good, go to the F150 forum and see how the 5.0 and Ecoboost boys are faring with mpg!