5.7L Hemi Multi-Displacement.. Gimmick??

[dholly]

5yr/0% on a 2006 Ram Quad 1500 w/Thunder Road pkg 5.70L Multi-Displacement Hemi, 5-Sp Auto and 3.92 axle. Test towed my [empty] car hauler just fine but window sticker EPA Mileage shows 14/18. If this engine goes to 4cyl on highway, why isn't the highway mpg better? Seeking comments/experience/enlightenment from Hemi owners please...

 

[thatguy]

In the Pre-Hemi 5.7 the rated mpg was something 11/13... so that increase is an improvement..

My bosses Vet (approx 2004 or 2005) has a multi-displacement engine and he says he gets close to 30 mpg on the highway.. i was surprised that it got that much

brian

 

[frank29]

I don't have a truck. I've got an '05 300C with that engine. For a relatively large, four door, 4200 lb car, that is one running machine...quick off the line, with plenty of passing power at speed. It also gets what I consider good gas mileage.

On trips with the cruise set at 80, I get 22/23 mpg. I'm sure it would get a lot better at slower speeds; but, when on a long trip, I just set the cruise 10-12 over the speed limit. Around town it gets pretty bad mileage, mainly because something is wrong with my right foot.

ON EDIT: I just pulled out my window sticker. The mileage was shown as 17 city/25 highway. So if your driving style is similar to mine, your expected highway mileage (sans trailer) is probably 14 to 16.

 

[Dargo]

The change in working cylinders is directly related to the power demand. If pulling even a relatively light trailer causes the computer to determine that the truck needs the additional power, you will remain on all eight cylinders. Even empty, but climbing a long grade on the highway will result in the same. The savings will be when cruising at speeds (in general) under 65 mph on flat roads without a strong head wind.

I know that sounds like a lot, but one of the major concerns of the manufacturers is to make sure that the consumer does not perceive the truck as feeling sluggish on the highway. A dealer I know very well said that he can change some of the computer settings with their Chrysler computer equipment, but the results are not what customers like because you can actually 'feel' the changes in displacement. The idea from Chrysler Corp is to make this displacement seem invisible. In other words, they are giving up a few MPG to make sure that customers don't complain that the truck 'feels' different.

 

[dholly]

Try as I might, I honestly could not feel when the fuel management system switched the Hemi from 8 to 4 cyl. On the Ram, the driver info display includes only avg mpg, not current mpg, but you could still tell it was working because the avg mpg would start up noticably after a few mins on a flat stretch. I assume having the trans in 'Tow' mode keeps the engine on 8cyl and I was avg'ing 12.4mpg pulling the car hauler around the back roads. I saw a high avg of 19.5mpg after about 5min of slightly hilly 55-60mph unladen driving. My bigget complaint about this truck was the front edge of lower seat cushion was too high, rather uncomfortable for my short legs. Pretty good hike up into the cab as well.

Since posting I also discovered GM's 2007 5.3L is a multi-displacement engine, so I took one of them for a drive to compare. That engine management system was seamless going from 8 to 4 cyl. also. The neat thing about the GMC was their driver info display included instant mpg and a V8/V4 light. You could clearly see when it flipped to 4cyl and the effect it had on mpg. I was impressed to see the mpg up in the mid-30mpg's cruising along at 65mph. With a little practice, I could quickly lift off the accelerator pedal and 'kick it down' to 4 cyls, even if I had been cruising along previously and the engine management system didn't do it automatically for some reason.

I admit I was skeptical of the technology but walked away from both test drives impressed. Don't have the bank for a new diesel and this sure seems like it eases the gas V8 'pain at the pump' some if you need a truck. I would be very pleased to see 18-20mpg+ avg. That's 20% better than my old '05 Sierra 5.3L (R.I.P.). Might be kinda fun too if, after taking an earful from the treehugger next door about your big, new gas hog, that it gets gas mileage roughly on par with his wife's mini-van. /forums/images/graemlins/smile.gif

 

[dholly]

frank - I have to imagine gearing will make a big difference in mpg figures with the same engine in car vs. truck too. One of the things I noticed between the Dodge and GMC is the 3.92 and 3.73 rear axles respectively. One would think the Ram's higher gears would be preferable* for those using their truck as a daily driver as well as weekend warrior tow vehicle. But... the GMC 5.3L window sticker was 15mpg City/21mpg Highway. Guess the bigger displacement 5.7L Hemi is noticably more thirsty. I just wonder how the EPA 'Highway MPG' is calculated with a multi-displacement V8.

*Opps, had that backwards. A numerically lower axle ratio results in lower engine rpm and better fuel economy. A numerically higher ratio improves acceleration, climbing grades, carrying loads or pulling a trailer.

 

[fluffyone]

i have always been a dodge fan, i had an 96 that has over 300000 miles on it and still going strong. but i had a new hemi and did not like it. the best fuel mileage i ever got even on the road was 12. the tranny went out twice in 60000 miles.

the new engine is not any better, i have a freind who has a new one and it is not any better. like i said i love Dodge and when the new challanger comes out i will buy one. but just know that fuel cost for the hemi will be expensive.

/forums/images/graemlins/blush.gif

 

[dholly]

Interesting, thanks. Seems rather odd mph would be no better with the new Hemi though, maybe your friend has a particularly heavy boot? I wonder if your problematic transmission was the same 5-Speed Automatic 545RFE Transmission I mention above?

 

[GeaugaDeere]

I have an 06 Quad Cab 4wd "Big Horn" Package with the 20" wheels. I'm averaging about 17mpg with mine, and don't do much freeway driving at all. I can tell you it's a nice upgrade in mpg and hp from my 2002 with the smaller 4.7 liter V8. I was averaging just under 15mpg with that engine, and felt it a bit overmatched for the 4wd quad cab's weight. The Hemi is a great engine, and I couldn't be happier with my new truck. I just hit 2000 miles and will be changing over to Synthetic (Mobil 1) Motor Oil on my first oil change and hope to gain an extra mile or two per gallon. The 2006 also has a new interior as well as an all new frame, suspension, quieter cab and front sheet metal. I will admit that I'm a bit biased towards Dodge...I work for Chrysler Corporation.

 

[slowzuki]

Of course you lost your solid front axle too if I've read the lit right. I know they did it to compete on ride but when really off-roading you can't beat solid axle trucks. The articulation, constant amount of clearance, and a high clearance area to get over tall stuff.

People still work to swap solid axles into brand new toyotas, ford 1/2 tons, chevys etc. At least the heavier models still have it.