Pros and cons of a Diesel?

[Tom]

Without one of the additional braking systems (such as engine/Jake brake, exhaust/Pac brake, or transmission retarder), a diesel has little or no braking, and the service brakes have to be used to slow/stop the vehicle. That would result in short life for the service brake components.

An engine brake works by effectively turning the engine into a compressor, releasing the compressed air (and energy) at the top of the compression cycle. See a fuller explanation on Jacobs' web site.

An exhaust brake works by electrically closing a flap in the exhaust system, creating back pressure to slow the vehicle.

As has been said, engine brakes are more effective in slowing a diesel than an exhaust brake. So much so, that some vehicles offer the driver several degrees of braking, which changes the number of cylinders used for braking.

 

[Oldgator73]

I had Cummins install an engine brake on our truck. They put it on the back cylinder. On the steepest grades out west I could put the truck in 3rd gear (5 speed) and engage the engine brake and never get over 30 mph and never engage the truck or trailer brakes. That was pulling a 37' triple slide triple axle 5th wheel.

 

[Tom]

Aye gator, when I've driven diesel coaches with multi-cylinder braking, I found myself reducing the number of cylinders.

FWIW when a CAT mechanic had the rocker covers off the big CATs in our boat (for maintenance), he explained the 3196 engines were both the same as used in over-the-road trucks at that time. He also showed me where they install the solenoids for engine brakes (not used on boats), and any combination or all six cylinders could have the brake solenoids installed.

 

[Oldgator73]

Most of you guys are smart on the mechanics  and Engineering of these things. All I know is I enjoyed the diesel truck. It powered up the steep grades with no problems and with the engine brake got us down the other side with ease. Now, mind you, this was back in the late 90's. Diesel was $.89 gal and this was before that DEF stuff was required for diesels. I just took the truck to Cummins when needed and got the required maintenance performed. Now, the Dodge truck it was in was a different story. The motor was built to last a million miles and the Dana 80 rear end contributed to the 3900lb CCC but the rest of the truck, the Dodge parts were basically crap.

 

[Larry N.]

It's the difference between an exhaust brake, and a compression (Jake) brake. the Beaver had a Jake brake.

I know, Tony. I guess I should have specified, but I was just trying to correct the impression that Arch left of the engine compression braking being an automatic thing just as it is on a gasser. Things work differently (and the Beaver was two stage, either three or six cylinders).

 

[Gary RV_Wizard]

What are the pros and cons of a Diesel over a gas motorhome?

Well, the diesel engine is part of it, but just one piece of "diesel pusher" vs a gas motorhome.

Diesels are used on larger/heavier rigs because it is the more effective way of moving big vehicles. Much has already been said here about engines and fuel, so I'll move on to the other aspects.

DP's have air brakes and air suspension. Air suspension is superior to leaf springs for ride comfort ans well as being auto-adjusting for changes in weight and weight distribution. Air braking has some technical advantages as well, so is the system of choice for very large & heavy vehicles.

A DP chassis is invariably designed to be more rigid and with greater weight capacity (GVWR & GCWR).  Some of that is because the diesel provides better low-rpm power, but some of it is simply that its a higher priced chassis that can bear the extra expense as part of the coach price (see below).  DP's enable the use of heavier components, e.g. real tile floors, solid wood cabinetry, larger appliances, bigger water tanks, etc.  Gas coaches max out at 22k-24k and 38 ft, so larger rigs with more amenities and upscale components are invariably diesel. You can have a few of the nice things in a gas rig, but you can't have them all because of weight and length considerations.

Because the diesel engine is so expensive, it pushes the coach into a higher price class. Thus, motorhome builders tend to put the other more expensive design attributes and components along with it.  There is a lower end to the  DP price scale, of course, but they generally still are better equipped than many gas chassis rigs. DPs generally start about where gas chassis coaches leave off.

 

[WILDEBILL308]

Well I wish the OP would come back and tell us what the coach is.
Bill

 

[Oldgator73]

WILDEBILL308
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

I learned my lesson with cats when I tried to take ours in the shower with me. Took the wife a good while to extricate the cate from my chest.

 

[timjet]

As Gary above has said, a DP is more than the engine. It was the other things that swung the decision for me to buy my DP. But the very reliable and often used Cummins ISL didn't hurt either.

 

[Gary RV_Wizard]

Putting it another way, a typical diesel pusher is a bundle (package) of enhanced chassis capabilities and house upgrades.

If the discussion is solely about engines, then the proper comparison would be something like Freightliner FRED or Workhorse front diesel vs the Ford or Workhorse front gas chassis.  Those are substantially the same except for the engine and are used to carry substantially the same size & equipped body (house). The Tiffin Allegro Open Road, for example, was available with either front gas or front diesel power, so an apples-to-apples comparison can be made.  The front diesel version has an increased GVWR (carrying capacity), gets slightly better mpg, and accelerates well without requiring high (noisy) engine rpms.