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Old 01-28-2023, 06:10 PM   #1
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Question Transition from gas to diesel

My wife and I have owned four gas RV's over 25 years, but are strongly considering a diesel pusher (specifically a Tiffin RED 340 38LL in our case) for long range national travel. My question is not about make/model/chassis, etc, at this time, but I need guidance in the driving and monitoring of diesel engines compared to gas. I know nothing about temperatures or pressures monitoring or about air brake systems. I need some pre-purchase tutoring before I invest in the change. Thanks for any guidance
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Old 01-28-2023, 06:52 PM   #2
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I doubt you will find the change difficult. As for the engine you monitor temp and oil pressure, same as gas. You will most likely have either an exhaust or engine brake of some sort. You will find this the largest change and a major benefit. The air brake system works just like a hydraulic system from a drivers perspective. There will be additional dash gages to monitor system air pressure.
The diesel engine will have much more torque than a gas engine. For a motorhome that weighs north of 30K lbs. it's the only way to go.
Some other differences:
Diesel costs more than gas
Oil changes will be 30 - 40 quarts depending on engine size
Fuel filters need to be changed frequently and you should carry a spare
Normal annual service for chassis $800-1000
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Old 01-28-2023, 07:34 PM   #3
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Transition from gas to diesel

Air bags, their systems and sensors are one thing when working but when and if they act up could affect ride height and leveling. Lots of systems and filters depending on models. Coolant maintenance is very very important.
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Old 01-28-2023, 09:04 PM   #4
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We had a 340 powered 38 Newmar LE prior to the current 360 hp we now own. I would advise driving that Tiffin on a variegated road test. Then drive other potential choices which have larger hp. We found the 340 a bit too weak to satisfy our needs. Make sure your potential toad is under 5K as that is the limit due to the Alison 2500 transmission which may be in the Tiffin 38.
Just my .02.
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Old 01-29-2023, 06:31 AM   #5
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We had a 340 powered 38 Newmar LE prior to the current 360 hp we now own. I would advise driving that Tiffin on a variegated road test. Then drive other potential choices which have larger hp. We found the 340 a bit too weak to satisfy our needs. Make sure your potential toad is under 5K as that is the limit due to the Alison 2500 transmission which may be in the Tiffin 38.
Just my .02.
Iím familiar with the Tiffin model line, your assumptions are all correct. The RED 340 line uses the Cummins ISB in 340/660 tune with the Allison 2500 transmission. Accordingly it has a tow limit of 5,000lb.

Also, it is built on the Freightliner XCS straight rail chassis so does not have passthrough storage, so something to check out and make sure it is adequate.

The OP doesnít say what in what state they are licensed. Moving to a coach with a GVWR above 26k may require them to secure a higher license classification - it does here in Texas. Regardless, I suggest finding your states CDL study guide online and learning the air brake section. How they work, how to perform a test, routine maintenance, etc.
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Old 01-29-2023, 06:57 AM   #6
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Diesels run hotter than gas. Usually 165-185, depending on engine & to some degree how hard it is working.

Diesels like clean fuel, clean oil & clean air. I have had three diesels used in marine applications & now the Isusu in my truck. Oil is cheap mechanic repellant. Use a better than specified grade of it & a better than specified filter. Get into a routine of checking fluids before a long drive.

Diesels are simple beasts but when something goes wrong hang on to your wallet.
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Old 01-29-2023, 08:57 AM   #7
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I have a Tiffin 37PA with a 360 HP engine and the Alison 3000 transmission. The 38LL would be much better with the same setup. That rig is too heavy for the smaller engine, and the 2500 transmission limits your towing too much. And I also have a XC chassis, and it does have pass through storage in the two big bays. That being said, the transition to a diesel isn’t too hard. You need to learn about engine braking and exhaust brakes, but temps and pressure limits are well marked on the dash instrumentation. The exhaust brake along is worth its weight in gold if you travel a lot in mountains.
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Old 01-29-2023, 10:18 AM   #8
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Originally Posted by hll60 View Post
My wife and I have owned four gas RV's over 25 years, but are strongly considering a diesel pusher (specifically a Tiffin RED 340 38LL in our case) for long range national travel. My question is not about make/model/chassis, etc, at this time, but I need guidance in the driving and monitoring of diesel engines compared to gas. I know nothing about temperatures or pressures monitoring or about air brake systems. I need some pre-purchase tutoring before I invest in the change. Thanks for any guidance
The newer diesel coaches are just like the gas coaches. The computer monitors all of your engine functions and will let you know if there is an issue. A modern diesel will not have overheating issues and again, the computer will watch for all of this. The big difference will be how the coach accelerates. A gas coach likes to have the pedal "mashed' for instant acceleration, but a diesel will just fall on its face if you try the same thing. Diesels are powerful but need to gain momentum versus accelerating.

Your gas coach uses hydraulic fluid, under pressure, to activate your brakes by putting pressure on the pads or shoes (drum brakes). A diesel (air brake) coach works differently. In the most basic description, springs are always applying the brakes on an air brake coach. It's the air that puts pressure against the springs, releasing the brakes. This is why it's important to know and maintain your air brake system. If the air fails, the brakes are applied, and the coach will come to a stop. This sounds serious, but rarely ever happens in the lifetime of people operating air brakes, especially in an RV.

Lastly, a diesel coach will come with an exhaust brake or engine brake. Similar to some of the grade brakes on newer gas coaches, the exhaust and engine brake basically block the exhaust from exiting the engine and cause a diesel to slow down. This is done in combination with the transmission downshifting. It's a useful feature when descending grades and towing a car or trailer. Operation of the exhaust or engine brake has a short learning curve, but can't be done wrong, just done better as you get more experienced.
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Old 01-29-2023, 10:43 AM   #9
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Hi ! Welcome to IRV2! Weíre sure glad you joined the gang here!

I don't know that much about Tiffin, but isn't the RED the one with the engine up front? If so, I would not want it, but that's just me. Hope you fine the perfect rig for your needs!

Good luck, happy trails, and God bless!
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Old 01-29-2023, 11:35 AM   #10
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Thanks for the feedback. I did not think the license situation would be an issue with a non-commercial vehicle in Alabama, but I'll check that. Sounds like I need to rethink the 340hp. We like that specific floorplan, but it sounds like it will be under-powered.
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Old 01-29-2023, 11:48 AM   #11
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Tiffin 360 RED

We have a 2020 Tiffin 33AA with the 360 engine and Allison 3000 transmission. These are a great match. Our RV is 35 feet long. Yours would be almost 40 ft. long. I think the 340 might be underpowered.

Good luck with your purchase.
Jerry
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Old 01-29-2023, 12:19 PM   #12
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Quote:
Originally Posted by Dutch Star Don View Post

Your gas coach uses hydraulic fluid, under pressure, to activate your brakes by putting pressure on the pads or shoes (drum brakes). A diesel (air brake) coach works differently. In the most basic description, springs are always applying the brakes on an air brake coach. It's the air that puts pressure against the springs, releasing the brakes. This is why it's important to know and maintain your air brake system. If the air fails, the brakes are applied, and the coach will come to a stop. This sounds serious, but rarely ever happens in the lifetime of people operating air brakes, especially in an RV.
To clarify what Dutch Star Don said above, only the parking brake is spring applied and air released. The service brakes are air applied and spring released.
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Old 01-29-2023, 05:48 PM   #13
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Hey jarwiebe, I think you need to take an air brake course.
Dutch Star Don is correct, the air works against the spring applying the brakes.
The park brake release the air from the brake chambers and the coil spring applies the brakes. You must have seen the twin skid marks on the highway. Generally caused by air loss to a set of highway trailer brakes causing full application by the spring and locking up the brake on that wheel
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Old 01-29-2023, 06:00 PM   #14
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If I recall correctly, and I could be very wrong, when we looked at this model I thought the salesman said that the coach has air leveling and no hydraulic levelers. Again, I could be wrong, but it stuck in my head and was one of a number of things that caused us to cross the model off our list.
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