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Old 11-25-2018, 06:49 AM   #1
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06 Crescendo 8356 300HP C7 poor MPG?

Just took an 800 mile trip from the panhandle of Florida to southern Tennessee and back. Six adults and pulling a Honda pilot on a tow dolly. had the water tank at about half but grey/black empty. Coach ran great with no issues but I wasn't really happy to get 6.6 MPG hand calculated.

I ran basically the speed limit up to +5 on the way up with a max of 75 for a few spots when I needed to feel like I wasn't getting run over around Atlanta. I decided to just stay at a max of 65 on the way back. Trip average was 6.6 MPG. This seems really low to me.

I just changed the oil before the trip (15w40 rotella T5) because the selling dealer had overfilled it. I refilled with 19qts and it stopped the excessive slobber....I got nothing in the slobber bottle this trip. I changed the air filter because the restriction gauge was at the top. I don't know when the fuel filters were changed, should I change them?

Power seemed ok, I don't have a lot to go on though, this is our first RV and we have only had it for about 4 months. I would lose about 5 MPH on a moderate grade on the highway..... 65 would slow down to ~60 whether I was on the cruise or not.

Are there any CAT software upgrades I should check into. What does the CAT software update that bumps up to 330 or 350HP cost? What about an aftermarket tuner, will that help mileage/power?
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Old 11-25-2018, 10:32 AM   #2
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JMHO: Speed was the big factor in you fuel economy , my best mileage comes when doing 58/60.
Here's a pdf from Cat on coach fuel economy .
I can get 9.5 mpg when cruising on the interstate, level road with no head wind , but an 8 year fuel mileage average is 7.8.
Attached Files
File Type: pdf Cat_RV_Performance.pdf (246.3 KB, 20 views)
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Old 11-25-2018, 10:42 AM   #3
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These Cat's are a thirsty engine. My C-7 330 hp gets right at 7 mpg driving a maximum of 65 mph, towing a Honda CR-V and full water tank. My old Cummins ISB 275 would get around 10.

Just my opinion, but the money you would spend on any engine upgrades would never get recouped by mpg increase, if any.
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Old 11-28-2018, 09:54 PM   #4
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My 3126-E gets average around 8 mpg. But my speed is generally around 60 mph. towing a 2018 Buick Envision Essense.

I find that those Cat engines with turbo need a air filter where the engine turbo gets plenty of air. I changed from the original Farr to a Racor air filter and the power increase tremendously and better fuel mileage then I was getting with the Farr. I order them through the internet. They run around $120.00
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Old 11-29-2018, 03:07 AM   #5
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Quote:
Originally Posted by RayChez1 View Post
My 3126-E gets average around 8 mpg. But my speed is generally around 60 mph. towing a 2018 Buick Envision Essense.

I find that those Cat engines with turbo need a air filter where the engine turbo gets plenty of air. I changed from the original Farr to a Racor air filter and the power increase tremendously and better fuel mileage then I was getting with the Farr. I order them through the internet. They run around $120.00
Thanks for the info. I didn't realize there were better breathing options. I just put on an OEM style wix air filter for 120.00.
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Old 11-29-2018, 05:11 AM   #6
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I do just under 65 and get 8+, we did a cross country trip (#3) this summer 4 adults 3 children towing a Chevy Treverse and the trip did 8.28 MPG total 6058 miles. We have a 2003 Winnebago Journey 36GD C7 cat 330hp with a Fram air filter.
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Old 03-25-2019, 09:08 AM   #7
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FWIW - I just read an interesting article about a modification to the HUEI pump (injector pump) where an additional oil filter is installed between the engine block and the pump.. I've read that these engines get dirty oil and that the oil filter doesn't get out all that it should and the small bits of dirt get into the extra fine tolerances of the HUEI pump...


The HUEI pump uses engine oil with a second pump to raise the oil pressure to 4000 psi to fire the injectors.... this is very high pressure oil and any dirt will contaminate the mating surfaces... CAT has found that an addition of a filter between the block and the HUEI pump will greatly extend the life of the pump and save several thousand in repair costs..


CAT has a kit for this modification, its not expensive but its means that the air compressor, and the power steering pump must be removed to install the kit....



With the price of the HUEI pump and injectors, I would add the kit as peace of mind... Just my thoughts...
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