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Old 12-07-2016, 07:02 AM   #1
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DP Motorhome for Dummies

Is there any type of book for someone that knows nothing about diesel motorhomes? I have been reading as many posts as I can concerning problems with them. Most of these posts scare me some. I am especially concerned about buying an used one that has problems that I could not see.
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Old 12-07-2016, 07:08 AM   #2
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Quote:
Originally Posted by reubenray View Post
Is there any type of book for someone that knows nothing about diesel motorhomes? I have been reading as many posts as I can concerning problems with them. Most of these posts scare me some. I am especially concerned about buying an used one that has problems that I could not see.
First remember 1 very important thing. Most people only post on the forums when they have a problem. For every problem you see here there are probably thousands of people that are happy with no problems. As far as picking a coach, find one you like and pay someone to inspect the coach for you. There are hundreds of posts here also telling you the kind of things to look for. Be wary but don't let it scare you away. DPs may not be for everyone but they are normally worth every penny for the upgrades you get over a gasser. Good luck.
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Old 12-07-2016, 07:35 AM   #3
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It helps to have a diesel 'background', as in, you owned a diesel truck at some point. However, as the poster above mentioned, having someone with diesel experience to look at the DP before you buy, might be a good idea. Or, get a PPI, a pre-purchase inspection from an independent shop. Hard to do on both dealer and private party purchases. If private party or dealer, the latter difficult, get as much previous work history as possible. Ours from a dealer, had none, 'protecting the privacy of the previous owner' they said! But, I have a diesel background and didn't care.

There are basically two engines, the Cummins and the CAT. I like the Cummins, had two in trucks beforehand. Ours is a 350 hp version in a 40 foot Winnebago Vectra, ok for flat-country travel flat-towing a heavy Jeep. However, on bigger, rolling hills, not much happening in the speed department. But it gets the job done. CATS have the same engine block, to a degree, and tweak the computer to increase horsepower, I think.
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Old 12-07-2016, 07:38 AM   #4
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Originally Posted by reubenray View Post
Is there any type of book for someone that knows nothing about diesel motorhomes? I have been reading as many posts as I can concerning problems with them. Most of these posts scare me some. I am especially concerned about buying an used one that has problems that I could not see.
Have an independent and unbiased PDI done on it, before closing the deal and make sure you pick a good one, that doesn't know the dealer or other from Adam.
After that, hope for the best, while learning what you can, along the way.
As said, you only hear about the small percentage with these problems.
Not that you won't have issues and everyone does, but that's something that goes with the territory.
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Old 12-07-2016, 08:50 AM   #5
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First remember 1 very important thing. Most people only post on the forums when they have a problem. For every problem you see here there are probably thousands of people that are happy with no problems. As far as picking a coach, find one you like and pay someone to inspect the coach for you. There are hundreds of posts here also telling you the kind of things to look for. Be wary but don't let it scare you away. DPs may not be for everyone but they are normally worth every penny for the upgrades you get over a gasser. Good luck.
What Jerry said!
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Old 12-07-2016, 09:00 AM   #6
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Yes by all means get someone to inspect it for you. Then we carry extended warranty coverage on ours because if we for instance blow an engine, we cannot afford to replace it.

Repairs on a DP will probably be at higher cost, but there should be fewer of them so it usually averages out. Maintenance is done less frequently than on a gassor so that averages out as well.

A DP is generally built on a heavier frame and along with a better ride there are many other advantages from it such as a heavier built coach body, ect.
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Old 12-07-2016, 11:11 AM   #7
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Aren't there more things that are different between a DP and a gasser besides the engine? A friend of mine had an air bag mess up. Do all DP's have them?
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Old 12-07-2016, 11:48 AM   #8
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Quote:
Originally Posted by Grenadiers View Post
CATS have the same engine block, to a degree, and tweak the computer to increase horsepower, I think.
Eh, not really.

Cummins have three common RV powerplants (depending on year)
ISB 5.9 and 6.7 liter (6.7 after 2005) - max 900 ft/lbs torque - more like 650 in early 5.9 ISBs.

ISC 8.3 liter - makes 1050 ft/lbs of torque in the 2000-2004 versions - and 300 to 350 hp

ISL 8.9 liter (basically a 8.3 liter with a longer stroke) - makes 1200 ft/lbs of torque and 360-425 hp.

Cats are 7.2 liter (c7) or 9.2 liter (c9)
C7s Tend to be similar hp as ISC but max of 850ft/lbs in <2003. Cats also had some issues with their HEUI fuel systems in the 2000 range.

C9s are basically similar to ISLs as far as weight, performance and service intervals.


Quote:
Originally Posted by reubenray View Post
Aren't there more things that are different between a DP and a gasser besides the engine? A friend of mine had an air bag mess up. Do all DP's have them?

yes.

Like others said find a local inspector. Ask if they will give you a copy of the report you will receive. Confirm the report checks for safe motivation - (Brakes have no leaks and stop safe, air pressure is adequate) Confirm the report checks for leaks (both engine and structure), Confirm the report has checks for electrical systems (both genset and chassis).
Ask if you can contact someone who has previously purchased a RV that was inspected by the company - (if they at least say you can then they are likely not fly by night)
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Old 12-07-2016, 02:11 PM   #9
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Quote:
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Aren't there more things that are different between a DP and a gasser besides the engine? A friend of mine had an air bag mess up. Do all DP's have them?
I don't hear of airbags failing very often but I do hear about the great ride you get on air suspension and the white knuckle ride and handling you get with non-air bag suspension! If you keep listening to the few and far between complaints about DP's normally from people with gassers, you will end up with nothing or something that is not as comfortable or efficient. This forum is full of people who have upgraded from gassers and are very happy. Yes you will find a few who aren't happy. Remember all the happy people aren't posting problems. Just the few unhappy people are. I've put 15K miles on my 2003 in 3 years and have had a few problems but...it has also taken us all over the country in comfort. Good luck.
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Old 12-07-2016, 02:14 PM   #10
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Eh, not really.

Cummins have three common RV powerplants (depending on year)
ISB 5.9 and 6.7 liter (6.7 after 2005) - max 900 ft/lbs torque - more like 650 in early 5.9 ISBs.

ISC 8.3 liter - makes 1050 ft/lbs of torque in the 2000-2004 versions - and 300 to 350 hp

ISL 8.9 liter (basically a 8.3 liter with a longer stroke) - makes 1200 ft/lbs of torque and 360-425 hp.

Cats are 7.2 liter (c7) or 9.2 liter (c9)
C7s Tend to be similar hp as ISC but max of 850ft/lbs in <2003. Cats also had some issues with their HEUI fuel systems in the 2000 range.

C9s are basically similar to ISLs as far as weight, performance and service intervals.





yes.

Like others said find a local inspector. Ask if they will give you a copy of the report you will receive. Confirm the report checks for safe motivation - (Brakes have no leaks and stop safe, air pressure is adequate) Confirm the report checks for leaks (both engine and structure), Confirm the report has checks for electrical systems (both genset and chassis).
Ask if you can contact someone who has previously purchased a RV that was inspected by the company - (if they at least say you can then they are likely not fly by night)
You are forgetting the CAT C-12 (12 Liter), 13 and 15. The C-12 is 1550 torque and they go up from there.
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Old 12-07-2016, 02:19 PM   #11
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How about the actual operating/driving differences?

I know to expect the maintenance to be much higher than a gasser, but what has to be maintained that is different from a gas rig?
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Old 12-07-2016, 02:50 PM   #12
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Quote:
Originally Posted by jimmy braden View Post
Eh, not really.

Cummins have three common RV powerplants (depending on year)
ISB 5.9 and 6.7 liter (6.7 after 2005) - max 900 ft/lbs torque - more like 650 in early 5.9 ISBs.

ISC 8.3 liter - makes 1050 ft/lbs of torque in the 2000-2004 versions - and 300 to 350 hp

ISL 8.9 liter (basically a 8.3 liter with a longer stroke) - makes 1200 ft/lbs of torque and 360-425 hp.

Cats are 7.2 liter (c7) or 9.2 liter (c9)
C7s Tend to be similar hp as ISC but max of 850ft/lbs in <2003. Cats also had some issues with their HEUI fuel systems in the 2000 range.

C9s are basically similar to ISLs as far as weight, performance and service intervals.





yes.

Like others said find a local inspector. Ask if they will give you a copy of the report you will receive. Confirm the report checks for safe motivation - (Brakes have no leaks and stop safe, air pressure is adequate) Confirm the report checks for leaks (both engine and structure), Confirm the report has checks for electrical systems (both genset and chassis).
Ask if you can contact someone who has previously purchased a RV that was inspected by the company - (if they at least say you can then they are likely not fly by night)
ISL is now up to 450 HP but still 1200 lbs ft torque.
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Old 12-07-2016, 03:09 PM   #13
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The best place to get info on driving and maintaining a DP may be at a CDL driving school. Some offer a course for RVers that will give you the basics on what you need to know. The DMV will have manuals for air systems.
DP's are far more complex than a gas coach but the power and ride comfort are well worth it. Most are on air ride suspension and they very rarely give problems if maintained properly. As with any RV maintenance is key.
There is a bit of a learning curve and there will be lots of ideas from other sources but getting from a professional source will be a benefit.
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Old 12-07-2016, 03:13 PM   #14
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In an attempt to try to answer your questions, here's my version of the differences (Diesel vs. Gas):
- Diesel coach weights tend to be heavier than gas. As a result, the tires can be a larger diameter able to carry heavier weights.
- Brakes. Diesel's are air brakes, versus hydraulic brake fluid on gas. There is an air compressor and air reservoir tanks, which are used to hold the air. You put your foot on the brake, and it pushes air to the brake air cylinders at each wheel, which puts on the brakes. Diesels will typically have drum brakes on the rear dual axle, and fronts could be disc or drums. If you loose air, the brakes go on. When you put the parking brake on, it releases air from the rear brakes causing the brakes to go on. Not sure about a gas RV, but a gas car will have a cable that goes to the rear wheel and apply pressure to a little drum brake. Diesel brake shoes will last forever.
- Suspension. A diesel will typically have air bags, which are between the coach and the axles. The coach is aired up to ride height by letting air from the tank into the bag. It is leveled by putting more air into the lower side, and taking air out of the high side. A gas coach will have metal springs between the coach and the suspension. So a diesel will ride smoother than a gas. There are sensors which determine ride height, and automatically adjust.
- Leveling at campground. By pushing a button, a diesel will dump the air from it's air bags lowering the coach to it's lowest position, then the hydraulic lifts will come down to level the coach. In a gas there is nothing to lower since you're sitting on the springs, so the lifts will start from the normal ride height position.
- Engine brake. A diesel will have an engine or turbo brake, which restricts the air going into the engine (or coming out of). So coming down a long medium grade the engine brake will hold back the coach speed by itself without applying the brakes. On steeper grades, you'll supplement the braking by periodically applying the air brakes to slow down and then release so the engine brake continues to hold back your speed. A gas, you apply the brakes and downshift if/as you can. (For me, the engine brake is one of the top three reasons I bought a diesel).
- Diesel engine is in the back, versus gas in the front. That effects a number of things. A diesel is quieter when driving because the engine is in the rear. Because there is no drive shaft running from the front to the rear, there can be more storage underneath. And since the diesel is in the back, the generator is in the front, so if you are boondocking and sleeping with the generator on, then it's at the other end of the coach as opposed to underneath the bed.
- There is more energy in a gallon of diesel, than a gallon of gasoline. Therefore you will get more mpg, and hence diesel will have a longer range. Add in the fact that diesel tanks can be larger (greater carrying weight), there can be a significant difference in range.
- I've had a couple different diesel cars over the years, and they tend to be solid engines that last forever. I've also got a diesel lawn tractor, acquired for longevity and power. There's nothing really scary about diesel engines.
- You do have to watch your diesel fuel, more so than gas. When diesel fuel gets into the 10-20 degree range it will start to gel up and won't go thru the filters. So they make a diesel additive that you put in your fuel if you travel thru that cold temperatures. In the summer when it's hot and humid, if you leave your tank empty you can get condensation in the tank, and algae can grow if you don't use your coach. Here again, easily solved by an additive and keeping fuel tank filled up. If you get algae it will clog your fuel filter, and the engine will stop because it doesn't get any fuel. Both of these conditions are easily avoided/managed.
- Not so important, but since you have an air tank reservoir, many diesels will have an air chuck so you can attach an air hose. I've filled tires and swim toys while on the road.
- Diesels tend to be heavier coaches, than gas.
- DIesel engines turn slower and torque is what matters. Under heavy load the engine may be turning 2000-2500 rpm. A gas engine will have to rev over 4K rpm, hence it's noisier.
- Diesels tend to be much more expensive than gas to purchase.
- Some say that diesels are more expensive for annual maintenance. They do have a larger oil tank capacity so change needs more oil, but I paid 200 bucks for an annual oil/filter change, chassis lube, and 2 fuel filter change.
- Diesels tend to have a higher resale value, and miles don't matter when buying/selling used, then can go multiple hundred thousands of miles. A gas coach with high miles however, will be discounted for the wear and tear.
- Diesel radiators are in the rear of the coach, gas in the front. Therefore on long trips a gas might be hotter up front (depending upon insulation), since all that radiator heat gets pushed into the front of the coach.
- I believe the front wheel cut can be more with a diesel than a gas , hence can turn tighter.
- Almost forgot one. Newer diesels use DEF to eliminate emissions, so the exhaust ends up being extremely clean water and nitrogen. They have a small tank (approx 10 gals) which hold this DEF fluid. You can fill it when you fill the diesel fuel and most stops, or buy it like I do at Walmart in 2.5 gal jugs for $8. You'll use about a gal for every 400-500 miles. I usually just carry two jugs and refill whenever it's convenient while sitting at a campground.

- Higher end larger diesels (can/will) have other differences as well. Tag axle to handle even more weight and rides nicer, heated floors, additional a/c's, diesel or all electric (ie no propane) heat, etc). I don't think that's what you're trying to understand so I've ignored all of those types of differences.
- Water and waste tanks between the coaches.....are the same.
- 120v, 12v, inverter, converter, batteries...typically are similar. Diesels can have some extra bells and whistles, but functionally very similar.

Those are the major typical differences I can think of.
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