7.3L to 6.7L comparison

[HMS_Beagle]

I replaced my '99 7.3L with a '15 6.7L recently. The two trucks are as identical as you can make from the order book: Supercab F350 dually 2WD Lariat 3.73 gears. For several years I have made the drive from home to Lake Tahoe, making this trip perhaps 40 times with the 7.3L, so I am quite familiar with the grades, fuel mileage expected, etc. The road climbs from sea level to 7200 ft Donner Summit and then drops into the 5900 ft Truckee valley, 165 miles each way. I set the cruise control on 63 when traffic allows. Hauling a 4300 lb Bigfoot 10.4E.

With the 7.3L, there were 13 grades which required a downshift to 4th. Practically this also meant dropping the speed to 55 due to the engine roar from the big gap between 4th and 5th. After crossing the flat Central Valley I would have about 15 mpg on the meter, maybe 16 if there was a tailwind. By the summit, this would have dropped to 12, sometimes 11.9, then picks up a little going down the other side. On the downgrade into Truckee, I had to downshift out of overdrive and ride the brakes a bit to keep the speed under control.

Today was the first opportunity with the 6.7L (also, the first trip with the air suspension - but that is another topic!). The gearing in top gear is pretty much identical to the 7.3L, but with 6 speeds spaced better in the transmission. It managed the whole climb in 6th on cruise control without apparent effort, no downshifting, no noise, no fuss. From the gages, it was working a bit, EGT peaked at 910 deg, oil temp at 242 (oil is designed to run hot in these engines), boost about 30 PSI on the steepest grades. Quite relaxing by comparison to the 7.3L. There was plenty of power to spare to pull back up to speed if I got caught behind a truck.

I had about 16 mpg on the meter when I hit the grade, it was down to 13.2 at the summit. Both trucks are about 1 mpg optimistic when checked by hand. On the downgrade into Truckee, the exhaust brake kept the speed at the cruise control set point though it did have to downshift to 5th to do it. No brakes required.

These new Superdutys are sure complicated and expensive - but they sure are nice!

[Vinsil]

BigToe wrote:

ppine wrote:
I pull with an old 7.3 with a few mods on it. I go by the tach in the hills. Running in high gear on a grade generates a lot of heat. I would use it to stay in the rpm range around 1,800-2,000 range or more when pulling grades.

I run a 7.3L between 2,450 - 2,650 RPMs when pulling grades.

With a pyro, it is easy to see the relationship between lower engine rpms and higher EGTs when pulling grades.

Ofcourse!You are very correct. Mine will pull any hill in 6th gear and builds heat to match...no reason for that, down shift and spin it up!

[ppine]

Big Toe that is a good observation.

[BigToe]

ppine wrote:
I pull with an old 7.3 with a few mods on it. I go by the tach in the hills. Running in high gear on a grade generates a lot of heat. I would use it to stay in the rpm range around 1,800-2,000 range or more when pulling grades.

I run a 7.3L between 2,450 - 2,650 RPMs when pulling grades.

With a pyro, it is easy to see the relationship between lower engine rpms and higher EGTs when pulling grades.

[ppine]

I have no experience with the 6.7 liter engine although people seem to like them. The transmissions are what has really improved in trucks in the last bunch of years.

By bolting on a 4 inch exhaust and a proper air intake, and adding a tuner, the older engines become more powerful and breathe much better. Getting the air in and out more efficiently, lowers the operating temperature under load. The mods on my truck cost about $1,200 which have long since paid for themselves. It is a lot cheaper than going to a different truck.

[ppine]

A good discussion.
Your trailer is not that heavy, but I don't like the idea of just running in the mountains with cruise control. I pull with an old 7.3 with a few mods on it. I go by the tach in the hills. Running in high gear on a grade generates a lot of heat. That is hard on the engine and the trans. Heat is what eats up diesels. The new transmission is a great asset. I would use it to stay in the rpm range around 1,800-2,000 range or more when pulling grades.

[dbhhcolor]

Sorry, been out for a couple days. Yes, looking at a Fleetwood Revolution with a Cat C9. The coaches I am looking at range from 22k-65k miles.

[Kayteg1]

New radiator for my Prevost was quoted $7000 about 8 years ago.
I was happy to recore it for $2400.
I was replacing head gasket on Mercedes engine just shy of 300,000 miles.
The cylinders were still having honing marks clearly visible. Meaning the engine was still in break-in stage.

[ticki2]

Maybe dbhhcolor needs to clarify . A Diesel Pusher s a rear engine diesel motorhome or bus . Is that what you are looking at ?

[Vinsil]

Steelhog wrote:

dbhhcolor wrote:
I am purchasing my first diesel pusher and wonder if mileage on the engine should be a significant factor. Should I overlook a rig with 65k miles and look more for a rig with 40k or less. Another factor is I am looking at 9-10 year old rigs. I am pretty comfortable with other considerations but wonder about the mileage.

Lastly, I plan to purchase a Good Sam Extend Service Plan to cover my butt...is this a good decision?

I haven't seen a diesel pusher yet with a "pickup truck" type engine. Typically you will find straight six heavy truck engines that can run 300,000 miles no problem. By looking in that age range most of the engines are pretty basic with mechanical injection and not much in the way of electronics. Biggest things with a diesel is a clean fuel system, fresh coolant and good oil. A Blackstone oil analysis is a good place to start when buying a used diesel.

Many had run the 5.9 Cummins which in all fairness, is considered a medium duty engine.

[Steelhog]

dbhhcolor wrote:
I am purchasing my first diesel pusher and wonder if mileage on the engine should be a significant factor. Should I overlook a rig with 65k miles and look more for a rig with 40k or less. Another factor is I am looking at 9-10 year old rigs. I am pretty comfortable with other considerations but wonder about the mileage.

Lastly, I plan to purchase a Good Sam Extend Service Plan to cover my butt...is this a good decision?

I haven't seen a diesel pusher yet with a "pickup truck" type engine. Typically you will find straight six heavy truck engines that can run 300,000 miles no problem. By looking in that age range most of the engines are pretty basic with mechanical injection and not much in the way of electronics. Biggest things with a diesel is a clean fuel system, fresh coolant and good oil. A Blackstone oil analysis is a good place to start when buying a used diesel.

[ticki2]

camr wrote:


My 2011 F-250 split it's rad at 41000 miles. I left the dealership $2000 poorer.

Holy smokes! $2000 for a radiator .

Higher mileage is not always a bad thing . It depends more on maintenance and where the vehicle lived it's life . Here in the NE a 10 year old vehicle with low miles that was stored outdoors can be a money pit . Things tend to freeze up or rot from non use , brakes , brake lines , fuel lines , bearings etc. . In the SW not so much .

[SoCalDesertRid1]

The lower the miles the better, provided it has been well maintained and not beat up.

[dbhhcolor]

I am purchasing my first diesel pusher and wonder if mileage on the engine should be a significant factor. Should I overlook a rig with 65k miles and look more for a rig with 40k or less. Another factor is I am looking at 9-10 year old rigs. I am pretty comfortable with other considerations but wonder about the mileage.

Lastly, I plan to purchase a Good Sam Extend Service Plan to cover my butt...is this a good decision?

[jimh406]

double post