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Old 09-07-2016, 08:44 AM   #1
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Seneca

Hi. I am in the process of purchasing a 2005 Seneca on a Chevy Duramax chassis. Most of the posts I have seen are from owners of newer Senecas on a Freightliner chassis. Any words of wisdom from the Chevy owners? I am curious about reliability, fuel economy, common issues and overall experiences.

Thanks in advance for responding.
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Old 09-07-2016, 09:22 AM   #2
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We bought our third motorhome last December which is an '08 Seneca 35GS on a 2007.5 Kodiak chassis with the Duramax.
We couldn't be happier and the Chevrolet side of things are rock solid.

A pre-welcome to the family.
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Old 09-07-2016, 10:40 AM   #3
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How many miles on your prospective purchase?

Bought our 2006 Seneca 34SS after a long bit of research. I owned a 2003 Chevy Crew Cab 4X4 Pickup with Duramax and Allison before. That was the LB7 generation of Duramax, which was the first. Solid engine with a weak set of injectors. Replaced the injectors 3X in the pickup. Two of those were under warranty. Third was out of pocket because it was >10 years old and no longer covered by the factory. $5k per swap. They changed the injectors and the placement of them in the change to the LLY generation. I think that occurred sometime in 2004, but not sure. You might check out what generation of Duramax you have in that motorhome, and ask a lot of questions of the previous owner. Some of the LB7s never had injector problems, some had nothing BUT injector problems. Seems a bit of a crapshoot. Remember that your chassis year is likely one model year before the motorhome year. So, your chassis is likely a 2004. My Seneca is LLY, so the injectors have never been a problem in 37k miles, and likely won't be until much later.

Seems new injectors, when done properly, yield about 40k to 60k miles. However, my first ones were changed at about 30k in the pickup as I recall. They have not changed the injector design for replacement injectors for the first generation (LB7), just the materials. And you need to ask the questions if they have ever been changed out. Even with new injector seat and plug materials, some have limited life.

Later generations of Duramax have different injectors and are much easier to change out if necessary. If you are getting a good enough deal on the motorhome, you may calculate that into the price and just get it done.

The best way to tell if the injectors need changing is to drip a few drops of engine oil from the dipstick, after engine is at operating temp, onto a folded paper towel sitting on a flat surface. After a minute or two, if there are two different color rings of oil soaked into the paper towel, one dark brown or black, and the other a dark amber, then you have diesel fuel in your crankcase. That is the surest way to tell without a complete analysis.

If you have diesel fuel in the crankcase, it will show up on the paper towel, and I would at the very least figure in about $5000 for the work. A Chevrolet Medium Duty Truck Dealer can usually check injector condition using the fuel return flow as a guide. They usually have the instruments to check it.

Aside from that, should be a reliable rig. Some minor issues on Kodiak chassis, but not much more than an annoyance that is easily fixed. Adding your own accessories is easy due to the tilt front end on these chassis, and service work on the engine is infinitely easier than any diesel pusher. You will find the Allison trans to be a joy to drive, and almost bulletproof. The only thing that kills them is heat when the owner doesn't pay attention to the trans temp gauge.

As for the coach, DW and I both love this. The previous owner corrected any flaws, and added a few handy options of his own. He didn't want to sell this one, but had to due to three daughters headed to college. He took pretty good care of it as well, and offered us a decent deal to buy it.

The Duramax/Allison is an excellent drivetrain for a Super C class motorhome, and I can enthusiastically recommend this package in most of its forms. If the power steering hoses which deliver fluid pressure to the power brake module aren't already replaced, you might also consider that. They eventually leak and weep, and most owners end up replacing them at some point. It's a pain in the ass, and is much more than a half hour job. I would recommend having it done unless you are used to such work.

Oil changes are personal choice. I did mine. It can be messy if you aren't prepared. And it's way more oil than you might guess. As I recall, ended up being 11 quarts with filter change. If they haven't done the trans fluid in the last 20k miles, I would do that, with BOTH filters (one inside the pan and one spin-on for the controls). Use GM Transynd fluid, and you will be happy with the results. This is one of those cases where there are a LOT of wrong ways to do this. Most trans fluid is NOT suitable for the Allison. Also, check your generator hours and do the air and oil filter and fluid changes if necessary. I use about 100 hours as a guide in the Quiet Diesel Onan.

Finally, they drive like a truck. Which means you will hear noises and squeaks, especially any rubber seals between the cab and the coach. Maybe a bit of wind noise at highway speeds, but nothing too annoying. Normal conversation should be easy. But it also means they handle the load of a motorhome coach very well, and have towing capacity well beyond many Class A units. Chassis is a brute, and suspension is very simple and solid. Headlights are a bit dim, and mine has high intensity halogen fogs under the bumper for supplemental lighting when necessary. Just don't use them with oncoming traffic. Drive in mountains using the temp gauges as your guide, and lock out of overdrive in the hills, don't get in a hurry, and you should be good. If it's equipped with an exhaust brake, use that. It will save lots of wear and tear on the brakes.

This is a very pleasant rig to drive, and I still get giddy at the whistle of that turbo, even after 14 years of owning a Duramax powered vehicle. We took this to Colorado just a few weeks ago, towed the Jeep. Everything worked flawlessly, and I was quite impressed with the drivetrain's ability to handle some big-league mountain highways. The turning radius will blow you away. Nothing like I expected. Just watch your rear end. It has a long overhang, and will swing out BEYOND the track of the outside rear wheels, and it's easy to hit gas pumps, railings, etc if you're not carefully paying attention.
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Old 09-07-2016, 11:58 AM   #4
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Many of 05's & 06's may be reprogrammable to make it a 6 speed, check with Allison. As Dustdevil said stick with Transyd fluid, trany runs cooler and needs less frequent changes. If you add a brake controller besure to follow Chev's bulletin 66 since you do not use the brake switch in the circuit. If you connect to the switch it causes it to fail. One other issue has been radiator leaks. GM had a batch of bad crimps causing seapage on the lower driver's side. I had two go bad so I switched to an all copper/brass radiator.

As been said overall it's a great MH put 55,000 on our 08 in 6 years and the radiator was the only issue. Avg fuel economy was 8.5 mpg towing a Silverado 1500. Only reason we traded was we wanted more room since we're full timing.

Add a set of KONI shocks and you will see a great improvement in the ride. Also have it weighed and follow MICHELIN's pressure chart for the tires. I ran 85 front and 90 rear with the 35GS
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Old 09-07-2016, 01:14 PM   #5
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Quote:
Originally Posted by Grumpy View Post
Many of 05's & 06's may be reprogrammable to make it a 6 speed, check with Allison. As Dustdevil said stick with Transyd fluid, trany runs cooler and needs less frequent changes. If you add a brake controller besure to follow Chev's bulletin 66 since you do not use the brake switch in the circuit. If you connect to the switch it causes it to fail. One other issue has been radiator leaks. GM had a batch of bad crimps causing seapage on the lower driver's side. I had two go bad so I switched to an all copper/brass radiator.

As been said overall it's a great MH put 55,000 on our 08 in 6 years and the radiator was the only issue. Avg fuel economy was 8.5 mpg towing a Silverado 1500. Only reason we traded was we wanted more room since we're full timing.

Add a set of KONI shocks and you will see a great improvement in the ride. Also have it weighed and follow MICHELIN's pressure chart for the tires. I ran 85 front and 90 rear with the 35GS
Great points. I haven't followed Michelin's chart, and run about 90 up front. I should check that chart. Been getting right about 10mpg overall. A bit better when losing altitude, even with occasional climbs thrown in. I would also think twice about full-timing in this 34. But I have no plans to full time any time soon anyway. I haven't checked how the exh brake is hooked up, but I'll look into that. It's an aftermarket system, so I have some homework to do. Thanks for the heads-up.
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Old 09-07-2016, 02:19 PM   #6
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Originally Posted by Dustdevil View Post
I haven't checked how the exh brake is hooked up, but I'll look into that. It's an aftermarket system, so I have some homework to do. Thanks for the heads-up.
Clarification: I'm talking about a trailer brake controller.
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Old 09-07-2016, 03:02 PM   #7
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Clarification: I'm talking about a trailer brake controller.
Oh, good thing. Mine had one of those. It's now in one of the storage cabinets, just in case it might be needed in the far distant future, LOL! It was trying to occupy the very same space usually reserved for my right knee.
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