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Old 04-03-2017, 02:36 AM   #29
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Originally Posted by RV-Writer View Post
What factors into the "abuse" rating?
Funny you should ask. We asked the same thing, then recounted to our friends at Cummins the anecdote that will follow the first part of my reply to your question herein.

First: so what causes the abuse rating? Keep in mind the conversation about this was brief and casual, but essentially it boiled down to over-revving the engine, pushing it too hard when towing or under adverse (read: mountainous) conditions, that kind of thing.

Now here's my personal observation and anecdote. Most people have larger engines than we do, from 350hp and up. When we start up a hill and the engine *begins* to labor, I immediately downshift and raise the RPM's to the proper "spot".

Others...well, they don't. I can honestly say I can't think of *one* time across the U.S., and back again this past month, that a coach followed along with us or got in front of us and took the hill slow and easy.

Without exception, every coach blew past us up the hill: diesel pushers of all ages, 5th Wheels, travel trailers, Class C's, gas coaches, you name it. Not just passing us most of the time, mind you: I'm talking going FAST up the hills.

As far as I could see, all but 1 or 2 made it over the hills without an issue. I seem to recall about that many during the round trip, parked by the side of the road near the crests of a couple of hills. But I'm more convinced than ever that many (but obviously, not all) people think because their coach can do it, they just should go for it at any speed they can manage.

More power to them (no pun intended); but before I buy a used coach from anyone down the road, we're going to have that sucker poked, prodded, and tested to the maximum extent possible. I know some coaches can handle that kind of thing just fine--but I'm still not convinced that it's good for the engines in them. After observing so much unnecessary pushing of diesel coaches up steep hills, I want to make sure we get an engine that has a good ECM report, good oil, etc. before we pull the trigger on another big purchase.

That's my two-cents, for whatever that's worth--which may not be too much.
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Old 04-03-2017, 07:08 AM   #30
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Originally Posted by ereadingrv View Post
Funny you should ask. We asked the same thing, then recounted to our friends at Cummins the anecdote that will follow the first part of my reply to your question herein.

First: so what causes the abuse rating? Keep in mind the conversation about this was brief and casual, but essentially it boiled down to over-revving the engine, pushing it too hard when towing or under adverse (read: mountainous) conditions, that kind of thing.

Now here's my personal observation and anecdote. Most people have larger engines than we do, from 350hp and up. When we start up a hill and the engine *begins* to labor, I immediately downshift and raise the RPM's to the proper "spot".

Others...well, they don't. I can honestly say I can't think of *one* time across the U.S., and back again this past month, that a coach followed along with us or got in front of us and took the hill slow and easy.

Without exception, every coach blew past us up the hill: diesel pushers of all ages, 5th Wheels, travel trailers, Class C's, gas coaches, you name it. Not just passing us most of the time, mind you: I'm talking going FAST up the hills.

As far as I could see, all but 1 or 2 made it over the hills without an issue. I seem to recall about that many during the round trip, parked by the side of the road near the crests of a couple of hills. But I'm more convinced than ever that many (but obviously, not all) people think because their coach can do it, they just should go for it at any speed they can manage.

More power to them (no pun intended); but before I buy a used coach from anyone down the road, we're going to have that sucker poked, prodded, and tested to the maximum extent possible. I know some coaches can handle that kind of thing just fine--but I'm still not convinced that it's good for the engines in them. After observing so much unnecessary pushing of diesel coaches up steep hills, I want to make sure we get an engine that has a good ECM report, good oil, etc. before we pull the trigger on another big purchase.

That's my two-cents, for whatever that's worth--which may not be too much.

A couple of points.
1. I'm not sure how you can over rev an electronic engine. They up shift and won't down shift according to the ECM programming.
2. Low rpm under heavy throttle will raise engine temps which is much more abuse than keeping the RPMs up close to the hp peak and will keep the engine cooler. Now I agree, that if you downshift enough to keep the RPMs up at less than WOT that is better for the engine. These diesels are designed to operate at a high load. Allowing the engine to lug down to the torque peak rpm is much tougher on the engine.
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Old 04-03-2017, 09:56 AM   #31
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Originally Posted by Steve Ownby View Post
A couple of points.
1. I'm not sure how you can over rev an electronic engine. They up shift and won't down shift according to the ECM programming.
2. Low rpm under heavy throttle will raise engine temps which is much more abuse than keeping the RPMs up close to the hp peak and will keep the engine cooler. Now I agree, that if you downshift enough to keep the RPMs up at less than WOT that is better for the engine. These diesels are designed to operate at a high load. Allowing the engine to lug down to the torque peak rpm is much tougher on the engine.
Just reporting the news, Steve.

Then again, during our discussion with our friends at Cummins, we all could have both been using the wrong word to describe the condition. As I said, it was a very brief and very casual conversation on the topic.

Let's replace "over-revving" with a variation on your word--lugging. I'll define it, at least for the purpose of this thread, as pushing the engine past healthy operating levels under adverse conditions, whatever you want to call those.

For example, in our case, it would be *very* easy for us to engage in "lugging" our engine—especially if we simply didn't care or were stunningly ignorant. The previous owner, when asked after our engine replacement if he ever downshifted to raise the RPM's to cool the old engine under hilly conditions, told us (with a baffled expression on his face): "Why would I do that? The transmission handles everything automatically, no matter what the road conditions are."

Sure. If only that were true. One new engine, 13,000 miles, and countless discussions with Cummins later, we can verify that he is incorrect.

One other thing: we've now visited multiple Cummins facilities in different states, from California, Oregon, and New Mexico to Florida. Each time, we inquired about a number of the diesel coaches in for service; this was on purpose, as we've grown quite curious about this subject over the past 18 months.

This is anecdotal, but of the coaches we observed at Cummins, the ratio was approximately 1 Onan generator repair or service to every 2 or 3 engine rebuilds or replacements, with the remainder of the coaches in for routine maintenance or odd repairs. I'd estimate the number of coaches at the Cummins facilities we visited to be around 3-6 at any given time, and that seemed consistent across all states.

99.9% of the coaches were considerably newer than ours; I don't think that means much, other than that there are a dwindling number of diesel coaches from the late 90's on the road. We do encounter them, but I’d swear we see far more older gas coaches than we do diesel.

Although this is also anecdotal, a high number of diesel motorcoach owners, in my observation, seem to be blowing up engines. Especially when those engines are rated at hundreds of thousands of miles when properly cared for. Granted, a number of those engine replacements and rebuilds, we were told, were due to poor storage maintenance followed by extensive driving without proper engine preparation.

Still, the number of damaged diesel engines due to poor driving habits seems unnaturally high to me. Maybe my opinion will change after another year or two or three of full-timing and talking to more people. We shall see. Either way, it's a topic that interests me more and more as we continue on our journey.
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