1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

6.5 Turbo reliability for an RV?

Discussion in 'Diesel 6.2, Conversions Cummins, etc.' started by mcarlo86, Aug 12, 2020.

  1. mcarlo86

    mcarlo86 Supporting Member Supporting Member

    Posts:
    180
    Likes Received:
    250
    Joined:
    May 17, 2019
    Location:
    ND
    First Name:
    Brian
    Truck Year:
    1990
    Truck Model:
    Suburban
    Engine Size:
    350
    A little background first: I have a '78 P30 Itasca class A motorhome with a 454, th400, and 4.56 gears with 235 85R16 tires. Currently the 454 runs like a top and I really have no complaints other than when I am towing a trailer with a couple ATV's on it or pulling my enclosed fish house trailer into a good headwind the 454 likes to run a little hot. I have had the radiator flushed and put a high flow 180 degree thermostat in it and that helped some, but I have to keep my foot out of it when pulling. Oh and when towing into the wind like that, its a 5 mpg adventure.

    I have been entertaining a 12V Cummins swap bolted to the TH400 with a Gear Vendors OD unit and probably re-gearing to 4.11's. The cost and complexity of that swap (along with the added weight to a already taxed front suspension with air bags) makes me wonder about other possibilities. First thing I could consider (and probably will be what I do) is look for a new aluminum radiator to help with cooling the 454.

    The other option I have been kicking around is finding an early mechanical 6.5 Turbo. I have had some people tell me that they can be retro fitted with the newer cooling updates and can be made reliable. I'm curious if anyone here has experience with 6.5's. I had a '97 K2500 with a 6.5 and it was a pretty decent pickup other than it would heat if towing in the hills. I like the idea of a 6.5 because it would be easier to bolt in, and weigh less than a Cummins, and should get better fuel economy than the 454. The biggest concern I have is keeping it cool because the motorhome alone weighs somewheres in the neighborhood of 11,000 pounds I think and it has the aerodynamics of a barn door. So, long story longer....would a 6.5 Turbo even be something I should consider?
     
    MrMarty51 likes this.
  2. bucket

    bucket Super Moderator Staff Member

    Age:
    38
    Posts:
    21,953
    Likes Received:
    7,724
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    I'm going to be right up front. It seems like a lot of trouble and expense to go to for less power potential, similar overheating potential and marginally better fuel economy.

    I know a 6.5 can knock down some impressive mpg, but that's in a truck weighing half as much as your RV.
     
  3. mcarlo86

    mcarlo86 Supporting Member Supporting Member

    Posts:
    180
    Likes Received:
    250
    Joined:
    May 17, 2019
    Location:
    ND
    First Name:
    Brian
    Truck Year:
    1990
    Truck Model:
    Suburban
    Engine Size:
    350
    Yeah, that is my gut feeling too. I had a mechanic friend who has a lot of 6.5 experience float the idea to me. I think first thing I should do is look for a better radiator. The 454 runs really strong and is a lot of fun to drive.
     
    MrMarty51 likes this.
  4. Blue Ox

    Blue Ox Turning Diesel Fuel Into Fun

    Posts:
    2,748
    Likes Received:
    4,226
    Joined:
    Mar 27, 2018
    Location:
    LI-NY
    First Name:
    Derek
    Truck Year:
    1985
    Truck Model:
    K20HD
    Engine Size:
    6.2L
    You would never recoup the cost in fuel savings.

    But if you're bent on it, you could convert a late 6.5L with all the updates into a mechanical engine by swapping in a mechanical injection pump. The only problem is used mechanical pumps for 6.5s are not common. But if you're willing to spend the money a fuel injection shop could build one for you. Or new ones are still available for about $2250.
     
    MrMarty51 likes this.
  5. Bextreme04

    Bextreme04 Full Access Member

    Posts:
    578
    Likes Received:
    533
    Joined:
    May 13, 2019
    Location:
    Salem, OR
    First Name:
    Eric
    Truck Year:
    1980
    Truck Model:
    K25
    Engine Size:
    350-4bbl
    Upgrade that 454, get a bigger radiator, and put some nice big electric fans on it to cool things down when it needs it. I got my donor 1997 Suburban with the MPFI 454 and 4L80E for $500.. tore the engine and trans down. Just got the engine back from the machine shop today. New everything, bored .020 over, new pistons, block cleaned and new cam bearings and plugs installed, rotating assembly balanced... $2,000 out the door. Should be somewhere around 400hp and 560 lb-ft of torque and get 13-14mpg with the fuel injection(you'd probably be closer to 11-12 in that motorhome on flat ground and down near 8-10 when loaded up or in mountains). The original motor and trans had 288,000 miles on them and were still going pretty darn good. You can probably find a motorhome that has the L-29 or L-21 in it for cheap that has been trashed but still has working drivetrain from 1996-2001ish. Either that or get an 8.1/Allison combo from an even newer one and just drop it straight in. You can find those with 100,000 miles on them for $3,000 or less usually.
     
    Craig Nedrow, MrMarty51 and mcarlo86 like this.
  6. Grit dog

    Grit dog Full Access Member

    Posts:
    598
    Likes Received:
    594
    Joined:
    May 18, 2020
    Location:
    Washington
    First Name:
    Todd
    Truck Year:
    1986
    Truck Model:
    K20
    Engine Size:
    454
    Swapping a 6.5 into anything sounds like one of the worst ideas I’ve heard in a long time.
    First, I wouldn’t put any more money into a 40 year old RV than absolutely necessary to keep it on the road.
    Second, the last thing I’d try to do is swap in a non-bolt in engine.

    I look at it like this. If I had the time to take on a crazy project like that to “save money” I’d use that time to make money and buy something that isn’t a rolling science experiment.
     
  7. MrMarty51

    MrMarty51 Full Access Member

    Age:
    68
    Posts:
    4,812
    Likes Received:
    2,974
    Joined:
    Oct 25, 2012
    Location:
    Eastern Montana
    First Name:
    Martin
    Truck Year:
    1978
    Truck Model:
    K20
    Engine Size:
    400
    I love My 2000 crew cab long box truck with the 4L80 and the 6.5 diesel, except when trying to get somewhere and the temps is over 100 degrees, the temp gauge is pegging about 220 and on the analyzer the temp is reading 217 through the ECM, not a fun day. A new radiator is going to be in the making right after I pull the current radiator and check to see if it is plugged up and or filthy durteee on the outsides.
    Without loading the truck or dragging a trailer, the truck gets a solid 18 MPG and that I like.
    A 6.5 would be the last resort for an engine for a rig as big as that, cummins makes more sense but, not as much sense as doing what is necessary to keeping what You have running cool, besides, the 6.5 would be real slow on the hills pulling that load.
     
    mcarlo86 likes this.
  8. bucket

    bucket Super Moderator Staff Member

    Age:
    38
    Posts:
    21,953
    Likes Received:
    7,724
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    How is a 40 year old RV any different than a 40 year old pickup? Are you saying we shouldn't put any effort into our old trucks to make them better or try different things? Most people with old iron aren't content with just "keeping it on the road" and there's nothing wrong with that. I'm sure Brian has the RV because he likes it, rather than because it was cheaper than a new one.
     
    mcarlo86, Blue Ox and Frankenchevy like this.
  9. Rickf

    Rickf Full Access Member

    Posts:
    124
    Likes Received:
    91
    Joined:
    Jul 29, 2017
    Location:
    Grafton NH
    First Name:
    Rick
    Truck Year:
    1974, 1954 & a 1937
    Truck Model:
    K20
    Engine Size:
    350
    You can still find 8.1L BBC's.
     
    mcarlo86, Blue Ox and The88 like this.
  10. Frankenchevy

    Frankenchevy Lying Dog-Faced Pony Soldier Supporting Member

    Posts:
    4,013
    Likes Received:
    3,900
    Joined:
    Jan 3, 2018
    Location:
    USA
    First Name:
    Jeremy
    Truck Year:
    Square
    Truck Model:
    CUCV
    Engine Size:
    Small
    I agree on just making the 454 work. Unless you’re a full timer, I’d bet that RV sees fewer than 5,000 miles a year. The ROI on swapping in a diesel would likely take a long while.

    I think the RV is pretty neat. I also like the old boxy winnebagos.
     
    mcarlo86, Blue Ox and bucket like this.
  11. mcarlo86

    mcarlo86 Supporting Member Supporting Member

    Posts:
    180
    Likes Received:
    250
    Joined:
    May 17, 2019
    Location:
    ND
    First Name:
    Brian
    Truck Year:
    1990
    Truck Model:
    Suburban
    Engine Size:
    350
    Yeah, I started this thread to float some ideas and see what people's opinions were on doing a diesel swap in an old RV. What I like about this forum is all the different ideas and how most of us here enjoy older vehicles. Truthfully, the 454 runs great and it is a blast to drive. There is only 34,000 miles on it as of today. It has been a lot of fun traveling around with the family. I get to drive a BBC and the kids get to hang out in a mobile living room. I have been averaging around 4,000 miles a year in it. This winter I probably will pull the radiator and see about either replacing it, or maybe re-coring it.
    An 8.1 would be an interesting swap with a 4L80E. Might have to keep that in mind if the 454 dies someday. That is a sweet '74 K20 in your profile pic. :favorites13:
     
    bucket likes this.
  12. nabeshin

    nabeshin functioning lunatic

    Posts:
    322
    Likes Received:
    410
    Joined:
    Jan 23, 2020
    Location:
    Cozad, Nebraska
    First Name:
    Grae
    Truck Year:
    1976
    Truck Model:
    K10
    Engine Size:
    400
    My family's old '91 class A motor home had a BBC engine, not sure on the displacement or fuel delivery. At any rate, my dad had straight pipes with no cats put on the thing. We'd sound pretty cool loping into the campgrounds like it was cruse night.

    So I recommend doing that at least.
     
    Bextreme04, bucket and mcarlo86 like this.
  13. Dooley

    Dooley Full Access Member

    Posts:
    138
    Likes Received:
    201
    Joined:
    Mar 19, 2014
    Location:
    North Coast
    First Name:
    RW
    Truck Year:
    1988
    Truck Model:
    V30
    Engine Size:
    454
    I like the 6.5 T in my 94 K2500 Suburban very much.
    Has the extra engine/transmission oil coolers and a huge radiator.
    Never over heated with any load I pulled.
    4L80E and 3.73 gears with 265/75-16's BFG Rugged terrain TA's.
    With camping gear and pulling the little rv trailer I have driven the entire circumference of Lake Erie on one tank of fuel using the cruise control and staying within the speed limit + 7mph. The diesel Suburban has a 42 gal. tank.
    I am familiar with BB performance in many of my own vehicles. The 6.2 an 6.5 will never match BB power as the BB will pass everything on the planet except a gas station in equal vehicles. I have seen a 2006 Silverado 3500 8.1 eat a Dodge Cummins up on a long grade.
    I own trucks currently with 2 with Duramax, two with Cummins 250, one ex-military with a turbo'd 6BT, Continental, Hercules, White, and a Detroit.
    Cheapest way to improve your old motorcoach is a perfect function cooling system and a lesser restricted exhaust.
     
    Last edited: Aug 17, 2020
    bucket and mcarlo86 like this.
  14. mcarlo86

    mcarlo86 Supporting Member Supporting Member

    Posts:
    180
    Likes Received:
    250
    Joined:
    May 17, 2019
    Location:
    ND
    First Name:
    Brian
    Truck Year:
    1990
    Truck Model:
    Suburban
    Engine Size:
    350
    One of the challenges will be finding a better radiator. It has a vertical radiator which appears to be somewhat of an odd ball. I'd like to upgrade to a bigger/better one, but not sure where to look. I should put a mechanical temp gauge in it as the current gauge just has C and a slash in the middle and then H. We took it to Medora, ND this weekend and running 55-60 mph, it stayed pretty much on the middle point of the gauge. If I tried to run 65+, then it would creep up to about half way between the middle and H. I am guessing that the middle point of the gauge is probably 210, but that is just a guess.

    As for exhaust, it does have factory dual 2 1/4" pipes. I have considered headers, but not sure if ceramic coated would put off more heat than the factory exhaust manifolds. Dont really want more heat under the doghouse.
     
    Last edited: Aug 17, 2020
  15. Craig 85

    Craig 85 Full Access Member

    Posts:
    2,749
    Likes Received:
    2,153
    Joined:
    Jan 25, 2017
    Location:
    Grass Valley, CA
    First Name:
    Craig
    Truck Year:
    1985
    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    My dad bought a 91 Southwind 34' motor home new back in the day. It was a '90 P30 chassis with a 454/TH-400 combo with no O/D unit. I don't know what gears he had, but it ran the 19" wheels. I do recall that rig having the stock mechanical fan, but also had dual electric fans IFO the radiator. He put about 70K miles in 12 years on that rig and I don't recall him ever complaining about over heating. He always had a 3000-3500 LBS vehicle in tow. Best mileage he ever got was 7 MPG.

    At 4000 miles a year, I don't think it would be too cost effective to do much other than the cooling system. If you found an O/D unit for cheap, then I might consider that. Lets say you go from 6 to 8 MPG. You're only saving about 160 gallons of fuel. At $3 a gallon, you're only saving $500 a year.
     
    Blue Ox and mcarlo86 like this.

Share This Page