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Old 09-06-2011, 05:34 PM   #1
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cummins or cat

I looking a DPs, what is the best engine to go with.
From the cat and cummins forums they both seem to overheat and low on power in the Rocky Mountains. I notice no DPs ever passed me in the mountains.
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Old 09-06-2011, 05:43 PM   #2
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Both are good engines. If you notice no DPs ever passed you in the mountains then why you looking a DPs? If that is what concerns you.
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Old 09-06-2011, 06:10 PM   #3
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We've owned both a Cat and Cummins DP, as well as 3 other gassers. We had far fewer problems with the Cat than the Cummins. Probably there are others here that would say just the opposite based on their experience.
We entered the DP market with a 97 Beaver Patriot with a 330 HP Cat. Great engine-absolutely zero problems. Traded it in 99 for a Country Coach with a 350 Cummins-lots of problems from day 1-Blowby problems with diesel fuel all over tow car, sensor problems, replaced fuel injection pump twice. Fortunately, most of these problems were covered under warranty which Cummins took care of very well, but lots of downtime in service bays and when you're fulltiming that's a real pain.
In fairness to Cummins, in that year that 350 was a pumped up 325 and in the first model year they had lots of redesign and fix it problems to correct. Later models seemed to be better.
After owning those two, we decided to stick with gas- far fewer problems, lots less maintenance $$ to service and keep running.
Just our personal opinion
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Old 09-06-2011, 06:19 PM   #4
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I have a 400 Hp cat. runs great never been to the rocky mountains but I have cross the smokey mountains several times no over heating. I also have never been passed by a DP or a gasser. The big difference a DP maybe in 4th or 5th gear when a gasser might be in 1st or 2nd gear.
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Old 09-06-2011, 06:32 PM   #5
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Cat vs. Cummins is like arguing Ford vs. Chevrolet. Either are good engines that will likely outlast the coach if properly maintained. CAT stopped making OTR engines a few years ago so you will see only Cummins in most DP's nowadays (except for the really high $$ coaches that might use Detroit Diesels).

Our 2002 330 CAT has been fine. Over heating issues you may have heard of are often related to rear radiator DP's with dirty radiators/charge air coolers. Rear rad DP's need the cooling pack thoroughly cleaned at least annually.

I pulled the Beartooth highway from Red Lodge, MT to Cooke City towing a 2008 4,700 lb Ford Explorer. The CAT ran fine and never over heated.
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Old 09-07-2011, 05:49 AM   #6
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Why am I looking at DPs? I blew up my workhorse 8.1 on Monark Mt and now a rebuilt. I have read on here how great DPs so I was hell bent to get me one untill I read the cummins and cat forums, all I see is overheating and 20mph up the big mountains in the Rockys.
I spend July and August in Colorado and all I ever see that climbing ok is the diesel PU and 5th wheel
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Old 09-07-2011, 06:33 AM   #7
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We've done the rockies twice in a gasser. Both times it got done. This year we upgraded to a DP. Haven't been out west yet, but it's still better, I'd keep it even if I had to push it.

Most of those problems seen in the 90's have been fixed permanently in newer engines.

Also, I like how our rear engine monaco puts the radiator and charge air cooler on top of each other rather than back to back.
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Old 09-07-2011, 10:15 AM   #8
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We've been all over the West and it's mountains for the past six years, first with a W24 gasser and now a C7 diesel. Both performed fine, and with proper driving technique, neither ever overheated. In your case, you don't sound convinced that a diesel will solve your personal needs, so I'd advise not to spend the money.
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Old 09-07-2011, 10:46 AM   #9
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Most of the people who switch to DP have not driven diesels before. They are different than gas engines! That is not just a no fooling.
You have to keep it in the power band of the engine when you are not just toodling along.
Remember the EPA wants the best mpg out of everything if they can not ban it.
My father did the Black hills and then got a recall for overheating. While not the Rockies he also never saw any overheating, but had the modifications made any ways. Last year he went to Rocky Nat Park and did not have issues while in that area. (I do not know his path to or ftom) He probably was doing 55 and I think once he said he did 45. When in hills like that he controls the trans.
This year I was able to switch from a v-10 to a diesel to pull my toyhauler. Pulls great.
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Old 09-07-2011, 11:29 AM   #10
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The best characterization I've heard between a Cat and a Cummins is the Cat is faster off the line and the Cummins is better at top end. I have no basis for comparison or even know if it's true, but if it is I know I spend more time at top end.
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Old 09-07-2011, 12:07 PM   #11
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CAT has more torque (initial power) and Cummins has better mpg for similar sized blocks. Cummins generally outlast CAT.

It is easier to find a Cummins repair shop if needed. CAT no longer makes RV motors.

I've been up and down CO I-70 many times. I do wish the MH engine was a size or two larger, but then I would also pay for it in less mpg. Keeping the rpm's in the power band is important. You'll need to know what the power band is for your motor. It differs from motor to motor.


Truckers say, drive the tach and not the speedometer when climbing. If you're in the power band with the correct gear, then that's all she'll do.

Go down the hill in the same gear you went up. Know what is right for your vehicle.

Downhill Braking:
- Keep the vehicle speed down. Use exhaust brakes if you have them and the area permits. Shift to lower gears.
- Brake some, then let off to cool. Brake some, then let off to cool. repeat allowing time for the brakes to cool. If you cannot maintain, pull over. I've seen truck tires on fire from the brake drums getting white hot. Plus, you can warp the drums and possibly crack them. Once the brakes get hot, the brakes will feel spongy. Too hot!! and they stop working.
- Don't let the vehicle go too fast since it takes way too much to bring it back under control again.
- I brake to bring the vehicle down say 10 mph, let it build back up and then brake again.
- I use a soft pumping action on the brakes.
- I do not hold the brakes down.
- I carry an infra red temp guage to check my brake temp when stopped.
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Old 09-07-2011, 12:08 PM   #12
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Quote:
Originally Posted by ron55 View Post
Why am I looking at DPs? I blew up my workhorse 8.1 on Monark Mt and now a rebuilt. I have read on here how great DPs so I was hell bent to get me one untill I read the cummins and cat forums, all I see is overheating and 20mph up the big mountains in the Rockys.
I spend July and August in Colorado and all I ever see that climbing ok is the diesel PU and 5th wheel
Guess it wasn,t all that fast !!!!
It all depends on what you want. I have a 34ft with a 330 Cat that passes everything and runs cool. They put the same engine in the 40fters. I doubt that it's all that fast in them.
Torque to weight my friend. Big show... No go !!
Buy a Motorhome for the floor plan without a consideration for whats underneath and it's a crapshoot.
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Old 09-07-2011, 01:02 PM   #13
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Originally Posted by ron55 View Post
I looking a DPs, what is the best engine to go with.
From the cat and cummins forums they both seem to overheat and low on power in the Rocky Mountains. I notice no DPs ever passed me in the mountains.
Cat no longer makes NEW diesels for RV's.However, they are trying to sell Cat branded trucks & engines (trash - dump)which are manufactured by Navastar- International & serviced by cat dealers.
If you are looking for a used coach & have a choice I would go with Cat. My 08 Cat-C7- 35 ft.goes up the Fancy Gap 7% grade (between Va. & WV.) in 6th gear (2nd overdrive) without downshifting at about 1850 Rpm. and never overheats .(not towing)----OVERHEATING & LACK OF POWER SHOWS A LACK OF PROPER MAINTAINANCE.
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Old 09-07-2011, 01:40 PM   #14
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Regarding the overheating problem, I think it's the result of improper or lack of maintenance and not the fault of the engine manufacturers. An initial proper and thorough cleaning of the radiator and every six months after, or immediately after driving on salted roads, will prevent any overheating problems as a result of insufficient cooling.
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Old 09-07-2011, 02:16 PM   #15
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Originally Posted by ron55 View Post
I looking a DPs, what is the best engine to go with.
From the cat and cummins forums they both seem to overheat and low on power in the Rocky Mountains. I notice no DPs ever passed me in the mountains.
If you find the DP you like and the powertrain is in sound condition, whether the engine is a Caterpillar or a Cummins would not be a "deal-buster" for me either way.

Overheating is not a normal characteristic of a diesel engine. Just like a gas engine, it could be due to dirty/fouled heat exchangers (radiators), a bad fan drive, faulty thermostat, low coolant or a number of other factors.

A turbocharged diesel engine is much less affected by altitude than a naturally aspirated gasoline engine. The naturally aspirated engine loses up to 4% of its rated power output for each 1000 ft increase in elevation whereas the turbocharger on the diesel engine will just spin faster as altitude increases to make up for the decreased air density (lb/cu ft) and shove more cubic feet of air per minute into the engine to maintain the same mass flow (lb of air/minute). The diesel engine may not show any altitude deration until 6-7000 ft elevation or more when the turbo finally maxes out on speed. This depends on the turbo match of that particular engine design.

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Old 09-07-2011, 03:03 PM   #16
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CAT has more torque (initial power) and Cummins has better mpg for similar sized blocks. Cummins generally outlast CAT.
The electronics in a Cummins ISC and ISL limit the torque output in the Allisons first and second gears. This is a result of testing that showed the trans couldn't take the initial torque of the Cummins. As far as I know the CAT's aren't limited.
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Old 09-07-2011, 03:04 PM   #17
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If you find the DP you like and the powertrain is in sound condition, whether the engine is a Caterpillar or a Cummins would not be a "deal-buster" for me either way.

Overheating is not a normal characteristic of a diesel engine. Just like a gas engine, it could be due to dirty/fouled heat exchangers (radiators), a bad fan drive, faulty thermostat, low coolant or a number of other factors.

A turbocharged diesel engine is much less affected by altitude than a naturally aspirated gasoline engine. The naturally aspirated engine loses up to 4% of its rated power output for each 1000 ft increase in elevation whereas the turbocharger on the diesel engine will just spin faster as altitude increases to make up for the decreased air density (lb/cu ft) and shove more cubic feet of air per minute into the engine to maintain the same mass flow (lb of air/minute). The diesel engine may not show any altitude deration until 6-7000 ft elevation or more when the turbo finally maxes out on speed. This depends on the turbo match of that particular engine design.

Rusty
Cummins says 10,000 ft elevation before you run into power decreases.
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Old 09-07-2011, 03:15 PM   #18
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Cummins says 10,000 ft elevation before you run into power decreases.
Yep, that's greater than 7,000 ft, as I said. It all depends on how much margin the turbo(s) have and how fast the OEM wants to spin them.

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Old 09-08-2011, 11:48 AM   #19
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We have owned 8 Motorhomes Gas & diesel The 3126/C7 cat Is appx, 450 CI. The chev 454 ford 460 Chry 440; The torque out put for the gas is near 400 foot lbs. the diesel out put is near 900 Foot lbs.( I don't want this to become a hair splitting post The figures are appx.) If you were passed by a gas Motorhome of equal Gross weight. Then there was a problem with the diesel. Another thing ,The gas engines are about 50,000 miles Engines ( I lost 3 of them) The diesel They say is a 500,000 mile engine... Some will say I know a friend that only got <<<>>>> miles. Well I know someone to, That lost there diesel . come over the mountian pass Dropped down the other side . well he never turned his Exhoust brake off and it kicked in trapping all that pulling heat in the engine and it Exploded;; That my friend has a bit of common sense;Not diesel problems, If you are going to keep the coach. Go diesel It's an investment. that you will enjoy and get more when you turn it.. Life is good
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Old 09-08-2011, 12:01 PM   #20
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CAT has more torque (initial power) and Cummins has better mpg for similar sized blocks. Cummins generally outlast CAT.

It is easier to find a Cummins repair shop if needed. CAT no longer makes RV motors.

I've been up and down CO I-70 many times. I do wish the MH engine was a size or two larger, but then I would also pay for it in less mpg. Keeping the rpm's in the power band is important. You'll need to know what the power band is for your motor. It differs from motor to motor.


Truckers say, drive the tach and not the speedometer when climbing. If you're in the power band with the correct gear, then that's all she'll do.

Go down the hill in the same gear you went up. Know what is right for your vehicle.

......... I carry an infra red temp guage to check my brake temp when stopped.
X2 on that.
My 190HP cummins carried the 18-19K combo up over monach pass at about 36MPH last month. I was in 4th gear @ 2500 rpm for the whole 9 miles up the east side. Once the clutch fan engauged I checked the gauges everry mile and all was well.
I did stop at the top and check everything.
And went back down in 4th as well.
A exh brake is in my plans.
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