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Old 09-07-2008, 02:25 PM   #1
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I have been a lurker and occasional contributor to this forum and am always impressed with the quality and thoughtfullness of the responses. I hope that someone can provide some insights for me.

I am a new (2nd) owner of a 2007 KSDP 3912 with the 350HP Cummings in the Spartan chassis. It had 6K miles at purchase and after 1K miles of travel I have a few questions.
1) It is averaging about 6.5 MPG compared to 9.5 MPG on my old (2000) 3126 Cat in a Freightliner chassis. This is dissapointing since the KSDP is only about 4,000 lbs heavier. Based purely on weight, pulling my 4,400lb toad I had expected about 8.5 MPG. (Measured weight is now 29,600 lbs fully loaded.)
2) Now that I can moniter the turbo boost I was surprised to find that on flat level ground at 60 MPH it registers around 20 PSI and uphill goes up to 34 PSI which fades to about 30 PSI after a few moments of wide open throttle. Also when coasting down long grades, the boost remains at about 5 PSI.
3) Engine temperature and Transmission temperature readings stay at 180F. I never hear the hydraulic cooling fan change speeds and wonder how to verify if it is working correctly. If I drive down a gravel drive with a cold engine while leaving a RV park, the dust storm blown up from behind would choke Lawrence of Arabia.
4) After startup, if I drive away immediately, the air suspension seems to be deflated and takes a few moments to come up to normal ride height. Both front and rear air reads above 100 PSI when this happens.
5) The slides operate very slowly. Subjectively, about half the rate of my previous Tiffen MH.


That said - I have been very pleased with the quality and liveability of the Newmar MH. The Spartan ride is noticeably smoother and the Engine is so quiet that I almost have to rely on the Tachometer to see if it is running. The Allison transmission is so smooth that you do have to look at the indicator to see if it has shifted gears.

Have a nice day - Darrel
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Old 09-07-2008, 02:25 PM   #2
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I have been a lurker and occasional contributor to this forum and am always impressed with the quality and thoughtfullness of the responses. I hope that someone can provide some insights for me.

I am a new (2nd) owner of a 2007 KSDP 3912 with the 350HP Cummings in the Spartan chassis. It had 6K miles at purchase and after 1K miles of travel I have a few questions.
1) It is averaging about 6.5 MPG compared to 9.5 MPG on my old (2000) 3126 Cat in a Freightliner chassis. This is dissapointing since the KSDP is only about 4,000 lbs heavier. Based purely on weight, pulling my 4,400lb toad I had expected about 8.5 MPG. (Measured weight is now 29,600 lbs fully loaded.)
2) Now that I can moniter the turbo boost I was surprised to find that on flat level ground at 60 MPH it registers around 20 PSI and uphill goes up to 34 PSI which fades to about 30 PSI after a few moments of wide open throttle. Also when coasting down long grades, the boost remains at about 5 PSI.
3) Engine temperature and Transmission temperature readings stay at 180F. I never hear the hydraulic cooling fan change speeds and wonder how to verify if it is working correctly. If I drive down a gravel drive with a cold engine while leaving a RV park, the dust storm blown up from behind would choke Lawrence of Arabia.
4) After startup, if I drive away immediately, the air suspension seems to be deflated and takes a few moments to come up to normal ride height. Both front and rear air reads above 100 PSI when this happens.
5) The slides operate very slowly. Subjectively, about half the rate of my previous Tiffen MH.


That said - I have been very pleased with the quality and liveability of the Newmar MH. The Spartan ride is noticeably smoother and the Engine is so quiet that I almost have to rely on the Tachometer to see if it is running. The Allison transmission is so smooth that you do have to look at the indicator to see if it has shifted gears.

Have a nice day - Darrel
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Old 09-07-2008, 03:13 PM   #3
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I have the Cummins 400 ISL, otherwise our coaches are just about the same.
My MPG was the same as yours until about 20k miles and I now get 7-7.5 MPG, not a lot more but every little bit helps.
My turbo boost reads the same as yours and my temps too. As for the dust cloud, it helps a lot to rotate your exhaust tip to blow out the side instead of down to the ground. Just be kind to pedestrians on the sidewalk and back off a little!
Upon startup I set the cruise to let the engine fast idle while the air gauges come up and I do not start out until I hear the back air valve blow off.
My slides are very slow also but I am a happy camper as long as they work.
Yours sounds normal to me so just enjoy.
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Old 09-07-2008, 03:36 PM   #4
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Well Darrel, Let's look at your questions.

Miles per gallon: A 350 Cummins starts to deliver better milage at 20,000+ (tires take 35 to 40k). It will not be like your Freightliner Cat combo. Mainly you will only have to look at total weight and performance to justify that difference.

Your turbo is a tottaly different animal than you are probably comparing it to. Thottle or load does not directly dictate the boost pressure. Your engine turbo has no waste gate, like most turbos used to, it controls itself with an ECM controlled noozle that is capable of 0 to 50 psi, should it deem it so necessary. Basically, no worries.

Engine and tranny temperatures are excellent, some run much warmer.

DO NOT DRIVE YOUR MH UNTIL THE SUSPENSION IS FULLY UP. Otherwise damage may happen to body and more. To accomplish this, always wait until your dryer dumps at top pressure. (An Air Gush Will Be Heard)

The slides on Newmar operate at the designed speed. Keep in mind, Newmar invented the flat floor slide and have done more inovative slide feature designs than any other manufacturers.

You have a Spartan Chassis. One of the best built, without question.

Your transmission is an Allison MH3000. You think it is smooth, obviously you have no yet done steep mountain grades. It's a bulldog, bullet-proof. You have the best.

Enjoy.

Peter
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Old 09-07-2008, 03:38 PM   #5
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Hi darrel,
Building on what Wayne posted, what I can add/support is:
1. I pull the same coach steet weight as you. My toad is 5075 lbs steet weight. After 3 years I average 7.4 to 7.7 MPG over a 3-4K trip. Traveling at 60 MPH on the Interstates.
3. Engine temp is the same as yours. Like Wayne posted, turn your exhaust to blow straight out. The dust storm will be eliminated. Go here to see an example.
4. Try this to make sure your suspension is fully at ride height.
* start the engine
* store the jacks
* As soon as the jacks start to store, leave the coach and do your final walk around.
* Once the walk around is completed, the jacks should be fully stored and the suspension up to ride height. Like Peter posted, the air dryer will let out a short gush of air.
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Old 09-07-2008, 04:55 PM   #6
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My 07 3910, like the others who responded, have the same numbers as you. I just turned 5000 miles today and driving between 55 and 60 am getting a consistent 7 mpg. I had a Winnebago witha cat 3126 330 HP and did much better with it thab I do now. I am getting what I expected for mileage and am kind of experamiting with speed. A consistent 55 MPH seems to get the same mileage as 60 MPH. The next trip will be at 65 (where legal of course) MY KSDP seems to ride rough or "harsh" on rough roads-worse than the winnebago, but better on good roads. Go figure! Based on weight I am lowering the pressure to 100 in front and 95 in the rear.
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Old 09-07-2008, 06:19 PM   #7
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Thanks for all your responses. Sounds like everything is about as to be expected. Maybe I'll also se better mileage in another 10K miles too.

Have a nice day - darrel
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Old 09-08-2008, 02:49 AM   #8
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Hi Darrel, in January of this year we purchase a 2004 Newmar DutchStar 4009 with the ISL 370 HP, Sparton, ect. Your summary expresses how we feel exactly.
1) On our trip from Florida to Ontario Canada we averaged 9.5 MPG, your concerns are justified.
2) I have no experience in this area.
3) Ours does the same thing but was assured this is normal...?
4) This is exactly as ours operates.
5) Same, but dealer said that this is normal.
This is our third MH & our first Newmar. So far it's the best yet.
Bill
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Old 09-08-2008, 03:07 AM   #9
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Bill & Marg, WELCOME TO iRV2.

Glad your DSDP is working well for you.
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Old 09-08-2008, 03:15 AM   #10
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">It is averaging about 6.5 MPG </div></BLOCKQUOTE>

My DSDP would only get about 6.5 MPG at first, and I found out the variable speed fan was always running at high speed.

Like your rig, I noticed great clouds of dust in campgrounds.

Once Spartan fixed the fan, my mileage immediately jumped to 7.5+ MPG and I'm about 39K GCW going down the road.
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Old 09-08-2008, 05:08 AM   #11
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Darrel

Welcome aboard the good Ship "IRV2"

I just rolled over 20,000miles on my Coach. I have a 330 Cummins and am averaging 8.6 MPG pulling my Jeep I am about 34000lbs. You do have afew more Horses to feed but I would think your MPG will get a little better.
I do not have a Turbo burst gauge
Engine Temp at 180 is OK it could go to 200 on a hot day and still be OK.
I would get the Fan checked It is a lot louder when it engages. and that could be a contributing factor to MPG and cooler Engine Temps.
Turning the exhaust ext will help with the dust.
After Start up give the bags a chance to fill before moving
The Slides are not fast.

Rick
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