Hemi 4/8 cylinder thought.
 

This may be totally wrong but I was thinking about the new hemis that half the cylinders shut off. My thought was, what happens after you've got 100,000 miles on it. Does it have 4 like new cylinders and 4 that are trashed or 8 spark plugs that are like new and 8 that are burnt? Just a thought.

RE: Hemi 4/8 cylinder thought.
 

I don't know the definite answer, but, the spark plugs are supposed to be replaced every 30,000 miles on the Hemi. So, I don't imagine spark plug wear is a major concern. But even more importantly, from what I've read, the cylinder deactivation is very minimal on a Ram. The only time I can imagine running on 4 cylinders is driving on the freeway, downhill, with the wind behind you. If you are driving fast, uphill, or into a crosswind, the truck is probably running on 8.

I think if you were to see 4 cylinders new and 4 trashed, you'd have to do 99.99999999999999999999999999% of your driving at highway speeds, coasting downhills. Of course, this isn't practical. Personally, I think the cylinder deactivation is more marketing than fuel efficiency miracle.

RE: Hemi 4/8 cylinder thought.
 

Well how the dealer explained it to me is that the motor will (on the 2006 and up RAMs) switch between 8, 6 and 4 cylinder modes while your driving and that its never the same set of cylinders that the computer is going to use. So like in 4-cylinder mode it will not always be the same 4. I bet it depends on when the computer decides it needs to change mode!

But maybe the guy didn't know anything about what he was talkin about? I have a 2006 RAM 2500 HEMI(R) as the multi-displacement system only comes on the 1500 in 2006.

RE: Hemi 4/8 cylinder thought.
 

You are right, the guy did not know what he is talking about. The engine never goes to six cylinders, it is either all or half.

RE: Hemi 4/8 cylinder thought.
 

Yar, I have one of these beasts. 06' 1500 quad cab MDS and I'm getting just a tad over 20 mpg on the highway, but life of the vehicle is in the low 15s. The MDS is supposed to kick in at cruising speeds: they state in the owners manual that using cruise control, going 65 mph or lower and easy accelerating will cause the MDS to kick in more often. As to which cylinders are shut off, it's the same 4 each time. And as was previously stated, it's either 8 or 4, no 6 involved. I've read numerous sites that quote dodge as saying that their testing shows no adverse wear on the engine. As for wearing on the cylinders, why would it matter? If the mds wasn't ever used you'd have 8 trashed instead of just 4.

RE: Hemi 4/8 cylinder thought.
 

Aren't salespersons a trip?:D Maybe he/she/it is remembering the awful old Caddy 4-6-8 system?

Squat: what rearend ratio do you have and what speeds to do you run when getting 20mpg? Curious. Thanks.

RE: Hemi 4/8 cylinder thought.
 

I just had my AT3030 install.....and now I can really tell when the MDS kicks in, still sounds good...but wish I could just turn it off when doing city driving...any ideas??

RE: Hemi 4/8 cylinder thought.
 

I've got the higher ratio 3.92. I find it amazing that something as simple as a little higher ratio gets you an extra 1k towing, not that I tow a whole lot - if I were to order the truck I probably would've gone for the 3.73. I'm running just over 60 mph (probably an average of 63) on a pretty flat highway when I'm getting just over 20. I have just a tad over 4k miles on it, does anyone know how many miles I need to have on this thing before the engine is completely broken in?? I've heard people tell me as much as 20k, but I'm thinking it's closer to 10k if I'm not there already. I'm going to get a spray in liner this spring and then I'll throw a bed cover on it and I'll see what I get then for mileage.

RE: Hemi 4/8 cylinder thought.
 

I'm not bashing the guys with the MDS on the new Hemis. BUT, did any of us really buy the truck to get good gas mileage? In the grand scheme of things, buying a truck with 345 hp, and hoping for good gas mileage, is like screwing for chastity. It doesn't make sense.

RE: Hemi 4/8 cylinder thought.
 

I got it because in the near future I'll probably be driving 50ish miles each way to work and that few extra MPG would help. I also do some farming stuff (hauling hay and such) so I needed to get a truck for that. And it's nice to get about the same mileage in a 30k truck as I would in a Cummings since I don't have the $$ to drop on a Cummings.