6.5 pros and cons

Discussion in 'Engine Performance + Maintenance' started by smdk2500, Apr 20, 2019.

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  1. SAATR

    SAATR /\___/\___/\___/\___/\

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    Problem with all of that is that it's used with an unknown history. One or more of the previous owners could have worked it like a rented mule, or worse.

    More air and fuel will make anything make more horsepower, that's the easy part. The hard part is keeping it together. That's the reason the 6.5 has been revised and outright redesigned up to the P400 spec engines, and those were only rated to 250hp/550lbft. If you can show me how to make a reliable 400hp 6.5 without sinking Dmax or Cummins swap money in one, I'm all ears.
     
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  2. letitsnow

    letitsnow I'm Awesome

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    Oh. I have a buddy with a 6.5 turbo that totally beats the thing. Never changes oil, never has any problems. I have another that maintains his and it blew up at 48,000 miles. He spends all of his free time trying to keep it running - has been doing the same for the past 10+ years. It seems to be a gamble.

    If it were my money, I'd try to find a gasser in nicer shape.
     
  3. Jaryd

    Jaryd Newbie

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    I drive a 6.5 everyday. It’ll do you good for a dd. As long as the pmd is in the bumper and you keep some type of lubricant in the fuel, change the harmonic balancer and belt pully And injectors every 100,000 miles keep the temp in check then there’s a good chance it’ll last you a long time. Never going to get 400hp from a 6.5 without doing crazy expensive upgrades like drop compression add a girdle, head studs, a hopped up db2 pump and a whole lot better turbo and much more.

    The 6.5 can be a good tow rig if you upgrade the water pump to the 2000 spin on fan clutch type pump and get the 2000 metal fan blade or Duramax fan and keep the coolant temp at 210 and NEVER HIT ANYTHING OVER THAT.
     
  4. skylark

    skylark I'm Awesome

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    Let's see, where to begin... First, I agree with @SAATR
    The 6.5 was based on the 6.2 which didn't have enough power to do much of anything but The fine folks at General Moturds decided to "compete" with the 5.9 Cummins powered Dog and the upcoming 7.3 Powersmoke. To do that they slapped an inefficient turbo on a larger displacement engine with crappy metallurgy. Then they used a cooling system that wasn't up to the task. They also rushed the electronic injection pump using, in my opinion, an underdeveloped control module (PMD). There are notorious for PMS failures (was that really a typo?...), cracked blocks in the main webs, cracked heads, overheating cylinder #8, injection pump issues, failed oil pressure sensors, complete cooling system failures, harmonic balancer failures resulting in sheared crankshafts, a crappy rubber balancer pulley, the wastegate system consists of failed vacuum pump, cracked plastic lines and solenoid failures, the turbos used were really undersized for their application resulting in high drive pressures causing excessive heat leading to cracking in the heads and valve failures plus additional heat to the already overtaxed cooling system. Oh, I almost forgot that oil cooler lines like to fail in dramatic fashion. Don't believe me? Just Google 6.5 and everything that I mentioned.

    I personally have owned 4 6.5 powered trucks. One I immediately sold. Two came to me with low mileage, 79k and 124k and both of those had valve failures. The 79k one had meticulous records including the additive and fuel mileage of every tank of fuel since new, every light bulb, oil change and truck wash. The fourth truck was my own personal truck and the #3 exhaust valve failed taking out the head, piston and possibly the rod as well. May it rest in pieces at 104k...

    I'm stupid enough to put a 6.5 back in my truck because I don't have Cummins swapping cash and I had already bought new hoses, glow plugs, injectors, upgraded turbo, mandrel bent crossover and more prior to the engine failure. Not too long ago I came across an Optimizer for a reasonable price. Do I trust it? NOPE! I've addressed every single issue mentioned above but prior to it getting back on the road I will renew my AAA membership.
     
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  5. 82c10step

    82c10step Newbie

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    Ouch. No love for the 6.5 in here.
     
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  6. skylark

    skylark I'm Awesome

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    I don't hate it either. I just don't trust it and I won't candy coat it's issues.
     
  7. 82c10step

    82c10step Newbie

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    It's actually my daily driver. No issues. Great fuel mileage.
     
  8. JCribb

    JCribb Old Army truck mechanic

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    To add to what @skylark said, I wouldn’t rush into owning a 6.5. I worked on this engine platform for over ten years in the Army, and we were constantly fixing dumb things, and I have changed more of these engines than anything else.

    I have a very well built 350, and I love it. If I was to ever own a GMT400 in a diesel platform, it would have a Cummins swap.
     
  9. Sparkysikes

    Sparkysikes I'm Awesome

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    Love the 6.5. But you don't race a 6.5. You let it get there at its own speed. I have the optimizer now with upgraded injection pump. I almost did the cummins swap. I love my 6.5 but will not claim it'll stay with a cummins. But I always stayed with my buddies 7.3. And his was modified. Since than I did the motor than the turbo hx35 and other than that just oil. Change every 5,000 miles fuel filter ever 15k and work on cleaning up the older body and interior. I do however have the mechanical injection
     
  10. phantom 309

    phantom 309 Newbie

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    I've had 6.5 diesels for 15 years or so,. I let it warm up before i push it,. I get them tuned for better performance, everybody knows about the pmd, so eveybody i know carried a spare with a spare cable.
    Open up the exhaust, if it has 4:10's or more put the hx35 turbo on it. I put 3:23's in my dd 2wd suburban so the small turbo is fine if you keep it below 2200. My 4x4 eclb is a 94 and it has a 5068 pump on it, program has it maxed out, pulls harder than any 6.5. I also did the 4 corner water line mod which keeps it cool.
    I added a cat 2 micron fuel filter and a larger fuel inlet to the pump. Factory fuel filter is a joke.
    Tiny fuel line from filter to pump.
    I was in the northwest all winter, on the drive back it got a steady 20.2 mpg
    Good injectors are the key to any diesel the 6.5 is no different. Pulls good enough for me, i have 284,000 miles on burb(us truck) and 530,00 kms on the 4x4
    I bought both trucks cheap, the more people who think them unreliable the better.
    Always warm them up,. Always cool them off,. It was way over stressed with poor cooling in military units and driven like gassers,. So they died easy. There's the internet world, then there's the real world.
     
    Last edited: Apr 22, 2019
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