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Caterpillar or Cummins?

RV Life and Travel Reader David writes...
(Choosing the Right Motohome Engine)

Caterpillar or Cummins? We are looking at a diesel and want to know. Does Cat or Cummins get better MPG? Which is the quietest? Which size engine for which size coach? Thanks.

Bob, the RVing editor's husband replies:

Wow, David, that's quite a bunch of questions! With the information you've given me, there are absolutely too many variables to definitively answer those questions. I'll give some of my thoughts, opinions, and opinionated knowledge that I've gleaned from others about diesel engines.

Caterpillar or Cummins, which gets better fuel mileage? I'm sure there are charts and tables that show fuel consumption, for both, under specific loads. Do those loads correlate to the loads of the particular motor coach you chose, with your particular loading, under the particular driving conditions you encounter, with your particular driving habits and style? No. Those figures are just a starting point if you want to compare. Both Caterpillar and Cummins are highly regarded engine builders that strive to get the most power per gallon of fuel consumed for their customers.

Which is quietest? The engines themselves probably make about the same amount of noise. The muffling systems, the location of the engine, the engine mounts, the building of the coach body, the mounting of the coach body, insulation, and carpeting, all affect the amount of engine noise you hear inside the coach. Something as obscure as the shower stall, or what you pack in the lower storage bays, can affect the sound resonance and amplify the engine noise you hear. Your hearing may be more acute to certain tones than others, making one engine sound louder to you than to me.

Which size engine
for which size coach? I've been told by people I respect in this area that these horsepowers will adequately move these motor coaches down the highway:

250 hp - 34 foot
330 hp - 40 foot
390 hp - 45 foot

For the most part, a coach builder isn't going to put an inadequate engine in a coach, for fear of a reputation for building "dogs." That said, is "adequate" performance what you want? You can get 650 hp or more in a high end coach. You don't really need it, except for bragging rights. I can remember when I ran an 80,000 pound, over the road truck with a 270 hp Cummins. A 45 foot coach possibly weighs 45,000 pounds.

Summing things up, Cats have always had a certain snob appeal or elitism to them. Cummins has traditionally been more a bread and butter workhorse. Cats were once more complicated and costlier to repair and maintain. Today, I don't believe either is less expensive in these respects.

Without a properly designed driveline, including the right transmission and differential gearing, any engine may perform poorly.

I have always preferred Cummins, but would be more than satisfied with either. Your engine is but one aspect to consider in your choice of a coach. Look at the layout, the interior, the storage, the price, the financing, the warranty, the dealership, the manufacturer, and a whole lot of other things. If my wife and I found a coach we liked, the engine would not be a deal killer to us.

We would also consider a Detroit. Detroit Diesel makes some quality, high performance engines.

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Cummins or Cat?
by: Bob H

Are you talking about a coach or a truck? I use a Ram truck to pull my 5th wheel. One thing I know is that the Ram truck with the Cummins diesel is the only combination on the road that does not require DEF.

Coleen the RVing editor ads:
I had no idea what "DEF" meant, so I did a quick search. DEF stands for "diesel exhaust fluid." According to, "DEF solution is used in Selective Catalytic Reduction (SCR) to lower NOx concentration in the exhaust emissions of diesel engines."

About the Diesels - 24 MPG
by: Anonymous Work Campers

We are traveling work campers for over 5 years now. We have a Dodge Cummins diesel.

Our first time to hit the road, I realized my exhaust was shot. So, once we got to Georgia, we had the total exhaust replaced It cost us over $600, but it was well worth the change. We have the four inch pipe, and we are pleased with the change.

We get about 24 mpg solo, and 12.5 mpg pulling our 35 foot 5th-wheel. The exhaust is noisy, but we have heard much worse; we are just glad for better mileage.

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