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!

[Jimster]

Beagle, I just picked up a 2016 F-350 Dually with the 6.7 engine and would like to monitor EGTs. How do you do this? I can't find an EGT display in the truck's display system. Thanks

[RedRocket204]

Golden_HVAC wrote:
My sister bought a 2016 F-350 dually to replace her 2013 F-150 with ecoboost. It pulls their 7,500 pound toyhauler very well now, even in the mountains of Colorado.

Yep! It will be nice when I finally get me a truck camper(new DRW too) but for now, I load up my 750-800 lbs Yamaha Grizzly in the SRW 6.7L F350 truck bed and pull my 8500-9000 lbs TT in and thru the Rockies without any problems... which is over 12k passes. Good power through all of it.

[2BLAZERS]

The newer trucks are amazing on power, towing capacity, and price! My 2016 with the camper on is very likely faster than my 2005 running empty. LOL. And no, I won't go back!

[HMS_Beagle]

Mike008 wrote:
Question for the OP, did you have any performance work done to the 7.3?

No, my '99 was and "early 99" actually delivered in May '98 and therefore the slowest of the 7.3L turbo engines. I left it completely stock. I am aware there are a number of tuning steps that can be taken to increase power, just as there are with the '15, in case you find 860 ft lbs insufficient for your needs. :).

In my comparison, both trucks where completely stock as delivered from the factory.

[Mike008]

Question for the OP, did you have any performance work done to the 7.3?

[NRALIFR]

Well I would hope that it has the latest flash on it since the build date of the truck was in April of this year, but I'll have them check it the next time it's at the dealer. After watching a couple more regen cycles yesterday, I think I must have caused the regen to stop. We were slowing down to go through a little town, but we never stopped. The next two regen's I watched went from "full" down to 15% while at hiway speeds.

To be honest, I don't know if my model actually allows a manual regen or not. That's a stationary process, and my understanding is the truck is supposed to ask you if you want to start it if the DPF is either "full" or "overloaded". Since I don't use the truck for stationary power or PTO use, it's unlikely I'd ever see those prompts.

That's a pretty sophisticated monitoring system you have there. Makes what I'm doing look pretty stone-age :). All I really want to do is keep up with when a regen is needed, how long does it take, and how many miles does it go between regen's.

:):)

[HMS_Beagle]

I had the DPF screen enabled when I bought the truck. It does not enable manual regen (though that is what the screen is called) on my model - that part of the feature is model dependent.

I continuously monitor all four EGTs, DPF load, percentage, regen intervals and about 10 other things. On my truck, the regen will start within a minute of the dash screen saying 100 percent, it will last about 20 minutes, and burn down to about 25 - 35 percent before shutting off. The DPF load reported on the dash and on OBD continues down for another few minutes as the exhaust is still very hot, ending up at around 20 percent on the dash and usually less than 1 g/l reported on OBD.

I wonder if you have the latest PCM flash, intended to correct the rare problems with 15-16 trucks during regen? That is supposed to make the regens behave differently - fuel is dumped into both banks, not just the left bank, and for less time according to reports.

Here is a captured regen with parameters plotted in XL. It is a little choppy because it started on the freeway, I pulled off and through town traffic for a bit, then back onto a hilly freeway:

[NRALIFR]

I've had the screen enabled on my 2016 F450 that allows you to monitor the DPF soot load, and was observing just today what happens when the exhaust filter gets "full". I've also got a Scangauge on it looking at several temperature points, one of them being EGT4. I'm assuming EGT4 is the last one, right after the exhaust filter. It usually runs at 600-700 degrees. When the exhaust filter got to "full", it started to regen and EGT4 went to over 1350 degrees. What surprised me is that it only cleaned it down to 80%, then stopped. This was all at highway speed, I didn't do anything that would have stopped the regen process. I guess the software knows what it's doing.

The DPF % Full screen is one of the screens that will appear under the Gauges menu if your technician will enable it. He may not want to enable it though because it also enables the ability to do manual regen's. You should never use that on your own.

:):)

[HMS_Beagle]

This '15 is 14,000 GVW, the '99 was 11,500, both dually F350. Which means in California, it isn't a pickup anymore.

With these highly electronically controlled engines, the amount of boost is set as much for smog and other engine management as for power. The '15 has no waste gate, but a variable vane housing. That's also what they are using for the exhaust braking function. The 30 psi was absolute manifold pressure read from the OBD port, so only about 16 psi above atmospheric. I think they run up to about 40 psi absolute.

One of the interesting byproducts of the immense electrical complexity is the ability to monitor literally hundreds of parameters via an OBD scanner and aftermarket display device (I'm using my iPhone with ForScan lite). There are four EGT sensors scattered down the exhaust system to watch, boost, turbocharger vane angle, DPF particulate load and back pressure, on and on. Occasionally I even look out the windshield too!

[Golden_HVAC]

There is one huge change between the 1999 and 2005 model years. The GVWR went way up. Your 2015 would have a 14,000 GVWR while the 1999 should only be 12,000 pounds or so.

Yes the extra horsepower is nice too! My sister bought a 2016 F-350 dually to replace her 2013 F-150 with ecoboost. It pulls their 7,500 pound toyhauler very well now, even in the mountains of Colorado.

Have fun with the new truck!

Fred.

[Vinsil]

30 psi? Yikes, your pushing it pretty hard!

I've only seen spikes to 32-35 psi playing around and seeing my charger effiency in the upper limits.

Maybe the scorpions run like that but i see 17-21 psi holding 65 mph up the steepest grades.

Just pointing out...if your truck needs 30 psi to hold the speed limit and your not just posting a spike, I'd question if that was normal because that is near the limit of charger effiency the engine is working hard.

Sorry for spelling, on my phone.

[HMS_Beagle]

ClassicB wrote:
There's no doubt the new F350's are nice and powerful but I will hang onto my bullet proof 7.3 as long as I can. Wait until you have to throw a new radiator into your tuck at 40K miles.

That's what the extended warrantee is for :).

I was a little reluctant to part with the 7.3L for that reason - in 18 years of ownership, it racked up $275 in total repair bills. With these new ones, a bit of water in the fuel and you are looking at a $12K repair bill. But it is soooo much nicer to drive. You can actually listen to the radio.

The new trucks from all the big three have issues - on Fords, it seems to be the fuel system (common with the Duramax), the radiators (there are two cooling systems), and the DEF/catalyst/DPF. But a couple of 2011 6.7L Fords have surfaced on the internet for sale with over 800,000 miles (documented) on the original engines, so they can last awhile if cared for.

[HMS_Beagle]

It was the 4R100, yeah 4 speeds not 5 (how soon I forget...). BIG gap between 3 and 4. It would bog down on the grades, then downshift. If I downshifted manually or with a heavy foot before it bogged, now it's turning 2700 rpm and giving me a headache. The gap was big enough one day heading north on US101 against about 40 knot headwind, I had to drive for several hours in 3rd.

In contrast the 6.7L has 6 speeds, and very nicely spaced. It is also much quieter and smoother, revving it to 2700 doesn't feel stressful at all - but it has so much torque this is seldom necessary.

Cleaner - it doesn't smell like a diesel running. You can wipe your finger inside the exhaust tip and it will be perfectly clean, no soot at all. The cost for that is an enormous amount of smog equipment which I am told is expensive to fix should it need to be.

[ClassicB]

There's no doubt the new F350's are nice and powerful but I will hang onto my bullet proof 7.3 as long as I can. Wait until you have to throw a new radiator into your tuck at 40K miles.

[Kayteg1]

Thanks for the review. I am surprised that much more powerful engine has the same top gearing.
I just upgraded my diesel sedan and when 174 HP diesel was turning 3000 rpm at freeway speed, the newer 210 HP turns 2000 rpm