Author Topic: C7 330HP engine performance  (Read 222 times)

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Offline c7smooth

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C7 330HP engine performance
« on: November 01, 2006, 11:22:29 AM »
Yahoo Message Number: 5005
We are new to the forum and new to MH moving from a 27' travel trailer. In September we purchased a 2004 Journey 36G with a C-7, 330HP engine. This is our first MH and first large diesel. My previous auxiliary Yanmar diesels were in a way different class. Owning a Cat engine seemed to me at the time of purchase to be a plus. Circumstances at the time of purchase required a Cat dealer to do a printout of the engine computer. With 18,328 miles on the engine the computer reported an average 5.7 mpg. At the time of purchase I was told, apparently as others have been, that I could expect 8-9 mpg. So the 5.7 mpg was a mild shock.
I assumed that I could do better then 5.7 mpg, especially after finding the Cat document titled "RV Performance Guide." So I turned on "economy mode" and have been montoring the instant fuel mileage as I drive and tracking the average mph. I am up to 6.5 mpg but we have only taken three short trips so not sure what the longer haul will look like. After reading many posts regarding mpg I am a little discourage by the realization that 7 mpg may be the top rung.

I have two questions that I am hopeful that more experienced C-7 owners can help with. (1) Has modifying the continous cooling fan opeartation by adding a thermostate made a sigicant change in the mpg and how expensive is this mod (discussed in the Cat performance guide)? (2) What are the postive performance chanrateristics of the C-7? Is there a good side to this engine?

Thanks,

Offline Joe Fischer

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C7 330HP engine performance
« Reply #1 on: November 01, 2006, 05:41:12 AM »
Yahoo Message Number: 5006
I used to have a 2004 Itasca Meridian 34H with the CAT C7. It's pretty much the same coach as the Journey. I averaged about 7.5 mpg until I got about 15,000 miles on it then consistantly got 8.0 mph. Are you figuring your mileage based on miles driven and fuel purchased or are you looking at the info center? The info center average mileage is from day one and will usually be lower than current mileage.

Joe Fischer

Offline jerryt12002

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C7 330HP engine performance
« Reply #2 on: November 01, 2006, 01:16:09 PM »
Yahoo Message Number: 5007
I have this engine in my 40ft 2003 Phaeton. I bought it with 13000 miles on it and I have put on another 7000 miles. On each trip I consistantly get 8.5 - 8.7 mpg. Just returned froma 4000 mile trip to northern Ariona and southern Utah (many big hills) and got 8.6 mpg. For the whole 7000 miles I am averaging 8.6. I should also ad that with 95% of the milage I am pulling a Jeeep Liberty toad (diesel). Generally drive between 60-65 mph. The milages you are getting seem awfully low since my rig is bigger and heavier, plus the Jeep diesel isn't a lite car.Jerry Timpe
Quote
I used to have a 2004 Itasca Meridian 34H with the CAT C7. It's pretty much the same coach as the Journey. I averaged about 7.5 mpg until I got about 15,000 miles on it then consistantly got 8.0 mph. Are you figuring your mileage based on miles driven and fuel purchased or are you looking at the info center? The info center average mileage is from day one and will usually be lower than current mileage.
Joe Fischer
« Last Edit: September 18, 2011, 03:45:56 PM by spuds »

Offline CRose

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C7 330HP engine performance
« Reply #3 on: November 01, 2006, 05:19:44 AM »
Yahoo Message Number: 5008
Charlie Rose here...
Shock and surprise club forms to the right...I think many of us were sold a mild bill of goods on the mileage issue. I had no lack of research into this, as I had rented for 4 years every other weekend before I bought (business related). I bought the Cat anyway because of how it moved my (lighter) coach, and the CHANCE that the mileage might improve. Let me tell you what I have experienced:

1) The Cat motors of recent vintage, along with many from Cummins et. al., are thirstier by far after about '99 or 2000. This is a generalization, and their are some exceptions, but I used to own a 99 Chieftain, about 25000 GVW that had a 275hp Cummins B-series, that ROUTINELY got 10 MPG, and 11-12 with favorable conditions. This motor is only 20% smaller than a C-7, so displacement should not yield the drop. The drop is due in part to emissions, and coach weight, though you and I share the same coach, 27910 GVW - mine is an Itasca Meridian 39'. Since the GVW's are not that far apart, that leaves me to believe that it is the electronic/emission controls that have reduced the mileage so much.

2) Cat Motors seem to be quite reliable in most respects, though they also seem to have the software issue bugs common to motors heavily dependant on software and electronic control, as the ACERT design is. Many software upgrades (re-flashes) have been offered by CAT for the C-7 and C-9 (I am told) which seem to be helping, but none of these motors routinely seems capable of anything higher than 7mpg+/-, unlike the older versions of the 3126 (b or e) which I am informed, used to get similar mileage to the B-series Cummins (9-11+/-)

3) Cat Motors seem to have a pretty good power/performance component. I actually prefer most of the Cummins products I have owned, but to tell you the truth, they were all much older than the most recent coach I purchased, and were un-choked by smog-control components and excess electronics. The Cat moves my coach well, but my coach, like yours, is light.

4) I think pound for pound, the Cat C-7 is a good motor, pretty leak free, and more than capable of handling coaches under 29-30k GVW as your and my coach are. Heavier than this, I am not sure, and it is AWFULLY complicated to "soup-up" a Cat motor (unlike a Cummins, there are very few products out there to modify fuel injection curves, boost and the like, and Cat, unlike Cummins is VERY sensitive about messing with their motors....just about instant voiding of warranty, even though this is illegal per se under the Moss-Magnuson Act). If you wish to improve the mileage or performance of a Cat motor, I would concentrate on the intake and exhaust restrictions, since mufflers and intake hosing/filtration is EASY to expand. I would also look at parasitic drag on the cooling system/fan clutch. There is a fueling box you can buy, which is cab adjustable, and does claim minor mileage/power improvement, but I don't need more power...just more mileage....

5) All Coaches have a "debug" period, and for some of us (not me) this has included motor re-flashes and other headaches..but you have a 14 ton home, mounted on a vehicle chassis....it really is amazing how bug-free, and how reasonably easy to correct these things really are....it's a lifestyle, to an extent, and you have to be preparred to put in your own effort, and to get on "the learning curve"...this is a good place to do exactly that....

6) It's a huge investment...some would even say "a money pit"...so if you don't use it...better to rent it out or get rid of it....they cost money just sitting, and they deteriorate (engine and chassis) as fast sitting, I think, as they do rolling...so you may as well roll regularly....I use mine for business and pleasure....

7) You have a brand name in both Cat, and Winnebago (I think you said yours was a Journey??) that should be easy to get serviced, though service at dealers is often a waiting game....make friends with at least one saavy guy in your local service dept. and whatever you do...don't piss him off....does not hurt to make sure he remembers you (in a good way...hello)

8) Plan ahead...extra fuel, oil, air filters onboard at all times...extra serpentine belt....full minor duty tool kit...and know your way around electrical systems.....dead batteries occurr mostly by not understanding the limitations (both design limits/flaws, as well as limits of laws of physics/reality) of your particular coach...example: My coach did not come with ANY battery disconnects...on-dash switch only....result: dead batteries...month(s) in service bays..no fix no matter what....solution: 9 dollars in spade switches on the battery posts...end of story, end of problem....

9) There is a strong consensus that these motors take some time to "break in"...I believe that to be true, and that mileage does improve a bit as they loosen up a bit...but you are unlikely to see this motor ever go from 7mpg (which I get towing or not, 70, 65, 60 or not within .2 MPG) to something in the mid to high 8's or low 9's. I just don't know anyone who has this MPG who is not in an earlier (2000 or earlier) 3126 b or e. I suggest to you that RANGE is more important than mileage, and with only 90 gallons, I have looked into custom tank manufacturers, as well as called Freighliner to see if the 100 gallon deep-rail tank from the Meridian, or the 150 gallon tank from the stacked-rail XC chassis would fit without dragging....not likely....one is way too deep, the other only yields another 10 gallons...not worth the expense. Custom tanks are possible, but placement of more fuel affects weight, axle capacity and alot of other issues....complicated unless you are an
 engineer, or wealthy/interested enough to experiment.....

10) Within the limits of the coach/engine combo, your driving methods are the single biggest predictor of mileage...but I find my coach is HIGHLY INSENSITIVE to variations in speed...I get 7.3MPG going 58....I get 7.1 going 65, or 70. So...I drive the highway comfortably...whatever that is....

There is more to tell....but that is a mouthful above...hope it helps....

Good luck...
Charlie Rose


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« Last Edit: September 18, 2011, 03:46:08 PM by spuds »

Offline Bill Zucker

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C7 330HP engine performance
« Reply #4 on: November 01, 2006, 08:12:19 AM »
Yahoo Message Number: 5009
I really enjoy reading this sort of thing from knowledgeable people - thanks Charlie.

What I've gathered is that ACERT does cost in terms of mileage, but one trip around back says it's worth it. I despise diesel exhaust, but the stream coming from our '04 Discovery (C7 330HP) doesn't seem to bother me, at least idling.

One thing about mileage also: be sure you have the latest flash update for your engine. Our engine arrived with 2457556, and like many other C7 owners, had a MPG reading from the Information Center stuck on 5.9. When I got 2725313 (the 9th since what ours shipped with), the reading jumped to immediately 6.9, which is what the total miles over total gallons works out to when the math is done right in the computer. Recent measurements (fill-to-fill gallons and miles traveled) show between 7 and 8, depending on driving conditions.

The MPG reading from the engine computer will always included pre-break-in miles and any problem period since day one. I'm trying to place a bug in Cat's ear that this measurement is meaningless and helps nobody even when correct. They should clear subtotals when you reset your trip meter, and measure MPG from that point.

Here's a distillation also of some Caterpillar published info for motorhomes I found at the local dealer:

  • Engine Oil: 19 quarts (shallow oil sump), replace every 11K miles. Install oil filter DRY. After 19 quart refill and running engine for at least one minute then waiting at least ten minutes, check level on dipstick and re-mark level as "Full" if necessary.
  • Blow-by: Caterpillar is aware that, by not extending your engine blow-by tube past the radiator, you can clog the radiator and overheat the engine, but Cat has no control how the engine is mounted in a coach. Motorhome manufacturer positions are that since Caterpillar does not have a recall on this, it's not their problem. Cat has recently released a "Blow-by Through Filter" (p/n 269-2002) that appears to include an extension out to the rear of the coach for $290 (plus installation), and claims to only need a new filter element "every three to five oil changes" (33k to 55k miles). If true, it would be worth it, but I'd worry about clogging it and having the engine suffer damage without knowing it. I've seen some C7 engines that produce very little blow-by and some that produce seemingly enormous amounts.
  • The aerodynamic drag of a car is around 0.3 (a brick is 1.0). Cat says the average coach is 0.6 but with some relatively vertical fronts and low airdams it might be appreciably higher. The air drag caused by vehicle speed (or a headwind) increases to the square of speed, and horsepower required increases to the third power (cubed). According to Cat, you'd need about 100 rear-wheel HP to go 55 MPH, but about 260 HP to go 80 MPH. So that 45% increase in speed costs you 160% more in power. Coaches with higher drag will require more than that. The numbers include a 70% increase in rolling resistance (tire drag) but which only amount to 40 HP at 55 MPH and 70 HP at 80 MPH. Be aware that a having a headwind of 20 MPH is about the same as driving 15 MPH faster! Cat's rule of thumb is that every 10 MPH over 55 decreases your MPG by 0.8.
  • Going up a 6% grade requires about 270 HP at 40 MPH, which is probably the most our 330 HP (at the engine) can produce at the rear wheels. This matches our experience pretty well. I was lusting after 350 HP, but know realize that it would buy us only about 3 MPH more going up this kind of hill. Apparently a simple reflash can get you from 300 to 330, but a lot more is involved to go from 330 to 350 HP. Freightliner chassis cannot dissipate generated heat already in some conditions so I'm not going to try to get more and risk frying things. It would take about 400 rear-wheel HP to maintain 55 MPH up a 6% grade with a 30k pound GVW.
  • Both cold weather and winter diesel fuel adversely affect mileage. The winter blend of fuel (#1), having a lower BTU content to avoid congealing, results in a 2.5% penalty (0.15 MPG). Compared to summer driving, 50 degree F operation incurs a 7% penalty (0.45 MPG) and 30 degree F operation incurs a 12% penalty (0.75 MPG).
  • A 10,000 increase in GVW costs an additional 0.55 MPG. Prorating, a 3000 LB. toad might incur a 0.2 MPG penalty.
  • Tires: Tire pressure 10 PSI low (95 PSI vs. the 105 PSI recommended for our Michelins for example) costs 0.5% lower MPG (or a measly 0.04 MPG less, too low to actually measure), but tire wear and safety dictate strict adherence to correct pressure. The best mileage will come when your tires are worn down because of lower rolling resistance, with most of that benefit seen when about half-worn.
  • Cat reckons that the range from the worst and best drivers is 6.0 to 7.5 MPG. Keeping it smooth, under 55 MPH and avoiding braking whenever safe to do so will maximize your MPG figures.
  • When calculating your MPG, ignore the Driver Information Center number (total vehicle miles divided by total fuel consumption). Calculate it yourself by elapsed miles divided by consumed gallons, preferably over a couple fuel fills. But remember to subtract any generator use of diesel fuel.
  • Resources: www.rv.cat.com, www.ohe.cat.com, www.catrvclub.org. Cat RV Hotline: 1-877-777-3126

Bill & Debbie Zucker
2004 Discovery 39J
« Last Edit: September 18, 2011, 03:46:38 PM by spuds »

Offline JimP

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C7 330HP engine performance
« Reply #5 on: November 01, 2006, 04:29:03 PM »
Yahoo Message Number: 5011

1) goto message number 1618 for a previous detailed discussion of the cost and return for the fan change
2) neither your 5.7 nor 6.5 are representative or typical of most other C7 owners experience. I would suspect the "electronic" report is invalid as a real mpg record. your actual measured 6.5 is still low, but you admit it was only short trips. stop and go driving will clearly drag your mileage way down since accelerating is when your engine gulps the most fuel. My actual, manually tracked at each fillup, record over 2 years and 12,000 miles has been 7.2 to 7.6 with it gradually increasing over time. My 2005 36' Discovery is in the same weight class as yours (28,000), and I tow a 4000 lb pickup. Since I'm still working, my free time is more valuable than my fuel mileage and I make no attempt to do anything to save fuel. I drive the legal speed limit or whatever speed is safe for the road & traffic conditions. My 12,000 miles is all out west and probably 70% on Interstates going 70 mph. from what I read here and on several other forums, my mileage is close to what most other C7 owners of this vintage report. but, yes there are exceptions at both end of the scale.
3) the benefits of the C7 engine are its dependablility, torque and
 power for our size/weight MH. I am more often than not, the one passing going uphill, rather than the one being passed.

just offering my feedback
Jim
Quote
We are new to the forum and new to MH moving from a 27' travel trailer. In September we purchased a 2004 Journey 36G with a C-7, 330HP engine. This is our first MH and first large diesel. My previous auxiliary Yanmar diesels were in a way different class. Owning a Cat engine seemed to me at the time of purchase to be a plus. Circumstances at the time of purchase required a Cat dealer to do a printout of the engine computer. With 18,328 miles on the engine the computer reported an average 5.7 mpg. At the time of purchase I was told, apparently as others have been, that I could expect 8-9 mpg. So the 5.7 mpg was a mild shock.
I assumed that I could do better then 5.7 mpg, especially after finding the Cat document titled "RV Performance Guide." So I turned on "economy mode" and have been montoring the instant fuel mileage as I drive and tracking the average mph. I am up to 6.5 mpg but we have only taken three short trips so not sure what the longer haul will look like.
After reading many posts regarding mpg I am a little discourage by the realization that 7 mpg may be the top rung.

I have two questions that I am hopeful that more experienced C-7 owners can help with. (1) Has modifying the continous cooling fan opeartation by adding a thermostate made a sigicant change in the mpg and how expensive is this mod (discussed in the Cat performance guide)? (2) What are the postive performance chanrateristics of the C-7? Is there a good side to this engine?

Thanks,

Offline c7smooth

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C7 330HP engine performance
« Reply #6 on: November 01, 2006, 07:03:26 PM »
Yahoo Message Number: 5013
Charlie and others, Thanks for the C-7 performance feedback. Helpful information and something I can work on. We're heading out this weekend for four days so will start manually calculating the mpg and see how it stacks up against the computer. Also, I am not going to over focus on the mpg as the intent was to use the MH at will and enjoy ourselves while doing it. But I am, and have always been, interested in making sure the equipment I own runs efficiently, dependably, safely and is able to do the job it was designed to do.
So that will be my focus and there in the mpg will take of itself. It is also good to hear that the C-7 is a strong engine and will perform as it was designed to do for our GVW. We mostly drive in the 60-62 range depending on traffic conditions and at this point tow heavy with a F-150 (5,550#). A lighter toad will probably help the mpg, but for now the F-150 is a "cellar." Again, thanks, Steve
« Last Edit: September 18, 2011, 03:47:24 PM by spuds »

Offline Dave Rehm

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C7 330HP engine performance
« Reply #7 on: November 02, 2006, 06:17:36 AM »
Yahoo Message Number: 5019
I don't have a C7 but rather the last version of the 3126, which I understand to be the 3126E. It runs great and is getting 7.84 mpg, including 222 hours on the generator. Mileage is determined by how many gallons of fuel taken on vs. miles driven. No other instrumentation used.

I have 25, 596 miles on the rig and am still on the original air filter. I noticed that the yellow thing finally hit the red mark so air filter will be replaced in the next week or so. Perhaps the mileage will be even better then.

Dave Rehm, W5KKC
'04 Tiffin Phaeton, 40 ft.

Quote
I used to have a 2004 Itasca Meridian 34H with the CAT C7. It's pretty much the same coach as the Journey. I averaged about 7.5 mpg until I got about 15,000 miles on it then consistantly got 8.0 mph. Are you figuring your mileage based on miles driven and fuel purchased or are you looking at the info center? The info center average mileage is from day one and will usually be lower than current mileage.

Joe Fischer
« Last Edit: September 18, 2011, 03:47:46 PM by spuds »