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Old 10-14-2020, 10:17 PM   #1
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Used Super C, C5500 8.1L or Duramax

Looking at a few Kodiak C5500 based motorhomes,
a 2005 Jayco with a 6.6L Duramax, 65,000 miles.
A 2006 Gulf Stream with 8.1 gasser, 25,000 miles.
the gasser has $10,000 cheaper asking price.
To be honest I'm leaning towards the gasser. No towing.
What's your opinions? Assuming both are in good condition and run / drive like they should.
Thanks!
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Old 10-14-2020, 10:58 PM   #2
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I've owned a 2003 3/4 ton GMC pickup with the 8.1 and my current motorhome with the 8.1.

I've put 96,000 miles on the motorhome and I like the 8.1 gas engine.

However....I'd sure look at the Duramax because going down mountains with the 8.1 is not much fun. Going up is fine, I don't mind going a bit slower.

The Duramax diesel would be great for going down mountains because the engine braking with a diesel is wonderful.

Is the fuel tank the same size on both RV's?

I have a 75 gallon tank and would pay a ton to increase my gas tank size. However nobody offers aftermarket gas tanks for my coach.
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Old 10-14-2020, 11:23 PM   #3
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Apparently the Duramax in the Kodiak, for certain years, has a bad habit of the engine cooling fans exploding. Just read a recent thread about that but cannot find it now. Its a design flaw for which there is no good cure.

The 8.1L for those old school folks is 496 cubic inches, basically a stroked 454. I have a friend with one in a 2500 surburban and he loves it. Its a hoss of an engine.

I am assuming since both are medium duty truck chassis, that they have Allison transmissions. I want to say the 6 speed was introduced in 2006 (chassis year) but not sure about this. That alone could be worth something.

Charles
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Old 10-14-2020, 11:50 PM   #4
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Hard call here, but as an 8.1L owner I have to say go with the 8.1 there are a few issues you need to watch on the 8.1L, mostly get a Scangauge II OBD-II unit and monitor the LF1 and LF2 fuel trims, as the 8.1L computer is bad about potentially going lean without setting a check engine light even though it should in case of bad MAF, O2 sensors, etc. and destroying the engine.
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Old 10-15-2020, 07:51 AM   #5
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Quote:
Originally Posted by Arch Hoagland View Post
I've owned a 2003 3/4 ton GMC pickup with the 8.1 and my current motorhome with the 8.1.

I've put 96,000 miles on the motorhome and I like the 8.1 gas engine.

However....I'd sure look at the Duramax because going down mountains with the 8.1 is not much fun. Going up is fine, I don't mind going a bit slower.

The Duramax diesel would be great for going down mountains because the engine braking with a diesel is wonderful.

Is the fuel tank the same size on both RV's?

I have a 75 gallon tank and would pay a ton to increase my gas tank size. However nobody offers aftermarket gas tanks for my coach.
I have a 34' motorhome with the 8.1 liter GM engine. I live in Colorado and travers 10'000+ foot mountain passes almost every time I leave home. I find the compression braking with the Allison transmission excellent. My previous gasser was a 7.4L with the 4L85E transmission and it did well with compression braking too. You just have to shift into a gear low enough the engine can hold it.

2005 and newer Class A motorhomes with Allison transmission had a "GRADE BRAKE" that provide automatic shifting for downhill grade control. Earlier models the driver had to do that.

On a 7% down grade in 1st gear the engine compression braking will hold speed to less that 20 MPH without using the friction brakes. I have no way to compare compression braking of the 8.1L to the "engine" braking of the DuraMax. It may not be as good but it certainly is adequate.

For every horror story about early engine failure with a 8.1L there is a horror story about early engine failure with a DuraMax. They are both great engines and perform long and well for almost everyone.
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Old 10-15-2020, 08:33 AM   #6
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We currently have a 2007 Jayco 33DS Greyhawk super c with the 8.1 and we previously owned a 2006 Chevy Silverado 3500 dually with the Duramax (towing a 40' 5th wheel) And I'll say this........I wouldn't trade the 8.1 for anything.
What a great engine and tranny set-up. Pulls hills as good as the Duramax ever did and absolutely NO issues going down grades either.
The cost of maintaining it is also much cheaper, less oil, fewer filters, less to go wrong all around. Only downside is a little less fuel mileage, 7 to 8 MPG overall with the toad attached. Then again towing with the Duramax was no great shakes either, got about the same mileage. And around here diesel is .75 to $1.00 a gallon more than the regular unleaded the 8.1 uses.
The Jayco has an 80 gallon tank so even at 7 to 8 mpg you get some good distance out of it.
Go for the 8.1, it won't disappoint!
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Old 10-15-2020, 09:22 AM   #7
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I have owned both older 2005 Super C units, 3 gas and one Duramax. I unfortunately was also a victim of the exploding fan problem in my 2006, which by the way was also a 5 speed trans. Fan exploded going up a steep hill in 94 heat pulling a trailer and car, so it was working. Destroyed the shroud and radiator, had to be towed off I-75, spent 3 days in a hotel waiting for a radiator to be shipped to a small town and installed, total cost was over $2000, and the tow was free!
As far as power I agree with the above poster, I was pulling a 9500 lb trailer with both, and went from NY to FL. with both, and they actually tow about the same, I didn't see any big difference, and the fuel mileage was only maybe a half to one mpg better with the diesel, but fuel cost was much higher. Could not drive enough miles to make it pay for the difference. Mine was bone stock, I am sure with a programmed ECM or tuner there is much more power available, never tried any.
Be careful of the front window models, they are prone to leak water, mine was bad, several thousand dollars were spent by 3 owners trying to fix it. My current one has no windows up front and I would never buy a super C with them, just my opinion.
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Old 10-15-2020, 11:12 AM   #8
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Quote:
Originally Posted by mlorlomoski View Post
We currently have a 2007 Jayco 33DS Greyhawk super c with the 8.1 and we previously owned a 2006 Chevy Silverado 3500 dually with the Duramax (towing a 40' 5th wheel) And I'll say this........I wouldn't trade the 8.1 for anything.
What a great engine and tranny set-up. Pulls hills as good as the Duramax ever did and absolutely NO issues going down grades either.
The cost of maintaining it is also much cheaper, less oil, fewer filters, less to go wrong all around. Only downside is a little less fuel mileage, 7 to 8 MPG overall with the toad attached. Then again towing with the Duramax was no great shakes either, got about the same mileage. And around here diesel is .75 to $1.00 a gallon more than the regular unleaded the 8.1 uses.
The Jayco has an 80 gallon tank so even at 7 to 8 mpg you get some good distance out of it.
Go for the 8.1, it won't disappoint!
I had a few more questions so I sent you a private message.Thanks!
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Old 10-15-2020, 11:36 AM   #9
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Perfectly happy with my 8.1 C5500 Jayco 33DS Super C. No problem on power and cant even tell my tow'd or trailered car is back there. It is a lil thirsty at the pump but the $15-20k difference in purchase price will buy a lot of gas... Maintenance is cheaper than the DMax and I believe the reliability is better as well.
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Old 10-25-2020, 08:47 PM   #10
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I own a jayco seneca 34ss with a the 6.6 duramax. The diesel power train is worth every penny. More power ,better fuel economy, longer life, engine brake. This unit will run all day at 1800 rpm towing my car trailer loaded and still get 10 mpg.
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Old 11-01-2020, 12:27 PM   #11
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Quote:
Originally Posted by Arch Hoagland View Post
I've owned a 2003 3/4 ton GMC pickup with the 8.1 and my current motorhome with the 8.1.

I've put 96,000 miles on the motorhome and I like the 8.1 gas engine.

However....I'd sure look at the Duramax because going down mountains with the 8.1 is not much fun. Going up is fine, I don't mind going a bit slower.

The Duramax diesel would be great for going down mountains because the engine braking with a diesel is wonderful.

Is the fuel tank the same size on both RV's?

I have a 75 gallon tank and would pay a ton to increase my gas tank size. However nobody offers aftermarket gas tanks for my coach.

Advice like this is just dangerous. Diesels have far LESS engine braking than gas engines. If engine braking on a down grade is a concern I'll take the 8.1 every time. The lack of engine braking on diesels is exactly the reason that exhaust brakes were invented.
A diesel with an exhaust brake does a great job of slowing a vehicle on a decent. Now that so many diesel vehicles come with exhaust brakes people make the false assumption that all diesels have them. They do not. As far as I know the Duramax engine never got an exhaust brake until the LML engine was introduced in 2010 so none of the MH Duramax engines will have an exhaust brake.
I had an 8.1L engine in a 2001 Dually. It was a great engine: smooth, quiet, powerful. It was almost the equal to my 2005 Duramax, but not quite. I drove a fully loaded 26' Uhaul truck from western NY state to VA; it had the 8.1L engine. I was really impressed with that truck. I thought it would be a dog in the mountains but it really did quite well. I'm also shopping for MHs built on the Kodiak chassis. I'd take either engine, all else being equal. I would have no problems at all with an 8.1L. The biggest disadvantage in my mind would be that the MH generator wouldn't be a diesel.
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Old 11-02-2020, 06:06 AM   #12
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You might want to check your facts on the exhaust break availability with the duramax engine. I know the lmm in my Seneca has it and I've seen earlier models the lbs with it. So it appears that it came in the heavy truck application well before the lml.
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Old 11-02-2020, 07:29 AM   #13
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My 06 Endura that had the LLY according to the Vin had a factory exhaust brake switch. It was almost too much deceleration and I didn't like seeing the higher engine rpm when you engaged it, it also dropped down one gear as soon as you lifted your foot off the gas.
Wonder if the increased engine rpm had anything to do with the exploding fan I got to experience??
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Old 11-03-2020, 07:35 AM   #14
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When I inspected my fan blades, I saw small cracks in a number of blades as if the nylon was drying out. So I replaced it. I take a look every oil change. It's been 2 years and so far no cracks.
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