I have a new 2008, 5.7 Hemi, 2500, Mega Cab, 4x4, 4.10 gears with approx. 2000 miles. I was particularly careful during the first few hundred miles to break the gears in (20 mile trips, then cool down...) and did notowing or hard engine accels for the first 1500 miles.

This last week I had to pull a trailer loaded with a golf cart about 150 miles, increasing in altutude from 1500 ft to 7500 ft. I used Tow/Haul mode the entire way.

There are times when the truck would downshift into the top second gear to keep the speed up. Is there any problem with running this engine at 4500 - 5000 RPM for30-60 seconds at a time? I will be making this trip often and need to know if I should just slow down, or if the engine can take it. The truck ran flawlessly, I am just concernedI am over revving the engine for too long.

I swapped this truck for a similar 2006 Mega Cab (everything the same except the NAV).On the 2006 Mega Cab, I had a two piece steel drive shaft, on this truck I have a one piece aluminum driveshaft about 6" in diameter. This is the longest and largest driveshaft I have ever seen, It is even bigger than the Duramax shafts.

What is the opinion on overall strength of an aluminum shaft this long. I have heard differing opinions on aluminum, some say the larger diameter isstronger than the smaller diameter steel shafts.

Anyway, any feedback on the RPM's and over revving the 5.7 would help.

 

You're not over revving the engine, redline i belive is somewhere closer to 7000. The only reason your rev's are higher is because tow haul mode reorginizes youe transmission gear ratios, giving you shorter grears that provide better torque for pulling a trailer off the line. DOn't know much about the drive shaft, you you should be okay with your engine, after all its the computer telling your tanny to shift.

 

you should be fine but i do recommend that if you are going to tow a lot make sure you use a good oil ( synthetic ) just works better under extream
conditions thats all .helps look after the investment

 

While I would not be afraid of operating at higher rpm to climb hills
it is unfortunately true that
both wear and friction
go up 8 times when rpm doubles.

So the minutes spent at 4000 rpm
are like 8 times as many minutes cruising at 2000 rpm
...the main effect is on wear on the piston rings
but the bore walls wear faster too.

At high rpm the metal areas around the piston pin and top of the connecting rod are also highly stressed...especially when the piston 'goes over the top' on the exhaust stroke end and the intake stroke begining. Many engines will break at this spot when over-rev'ed....or if the engine is getting old and worn.

Another worry is the valves "floating" at high rpm on old engines where the valve springs have seen many miles or have been over-heated only briefly.

In the pickup advertising & sales 'war' over horsepower
Dodge put the 5.7 V8 maximum torque at 4200 rpm
in order to get 'whopping' horsepower numbers.

It is really debatable if a 'truck engine' should have its camshaft create maximum torque over 2500-3000 rpm, since towing a trailer is not the same service as racing at a dragstrip.

 

Hmmmm!

Aluminum drive shaft in the new 2500's. I like my steel. The jury is still out on that one. Unfortunately, I think you are the Guinny Pig on that set up. The earlier aluminum drivelines on the 1500's have been subject to vibration issues, and a few here have exploded from balance issues. If you have the option to get an extended/lifetime warranty----I would.

Just a Heads Up!!!

 

Just a expirence. I towed a 8000lb trailer up a very steap incline going to a mx track in the middle of no where. my truck was in the 5000rpm range all the way up. for about 2 min. I could have sworn if we let off we would immediatley start rolling backwards. Thats when you know u need a desiel. Whatever my dad wants to get the 08 ford f450.

 

when we when up to the mountains during the summer we took my moms 04 hemi on 35's and it was running about 5k with no problems, while doing that I looked at he and said that I sure was glad I converted it to synthetic. never used a drop the whole time.

 

Thanks for the info. I don't intend to run it that way all the time, just when I need to get up the hill and not roll backwards... It ain't no Cummins!
When I take the same trip without a triler it screams up the mountain, I wonder what will happen when I get my larger tires. There goes the poop!

As for the driveshaft, I'm not kidding, This thing looks like a missile silo. I'll tell you this, I don;t get anywhere near the vibrations with this long one piece tube on this 2500 Mega Cab as I did with the two piece steel shaft on my 2006 Mega Cab.

If I change to synth oil, is there any special instructions to go from oil to synth? Or do I just tell the guys at Jiffy Lube to put synth in it?

 

I have changed all my past vehicles and my current one to synthetic, all you need to do is just put it in on your next oil change. And some people will tell you that once you go to synthetic that you cant go back to conventional. This is a myth becauseI used to do it all the time on my last car when I was low on cash lol... And I know of alot of people that have done it aswell.

 

yeah I am for one not a fan of aluminum driveshafts...reason being is the driveshaft on my truck exploded going down the interstate about 80 MPH...i'm having a steel driveshaft made this winter while the truck is being stored...if i was you, i would deffinitly look into a steel driveshaft