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Old 02-26-2018, 10:50 PM   #1
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Help!GMC 3500 6.5l should I?

Hey guys your the expert Iím new Iíve kind of been set on the 7.3 but I just found a 98 gmc 6.5 l diesel for only 3000. They say it only has 70000 miles on it which I hope is true. Are these good engines? She said it wasnít turbo diesel but I looked up the vin and it said it was a 6.5 v8 turbo diesel???? Would it be worth it any advice would help, thanks guys
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Old 02-26-2018, 11:30 PM   #2
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I had a mid 90ís suburban with the 6.5. Maybe something is different with this application, but it was the least reliable vehicle Iíve ever owned.
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Old 02-27-2018, 03:05 AM   #3
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Basically the same motor as whatís in the Hummer H1. They arenít big power houses, but very efficient. If memory serves, 195 HP 430 ft lbs TQ when new. Iíve had good luck with the 6.5liter, Iíve had both turbo and NA versions. Hope that helps. Good luck.
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Old 02-27-2018, 07:22 AM   #4
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I think the difference is in the injection pump. The mechanically injected ones were great the electronically injected ones were terrible. At least the ones used in GM trucks that is.
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Old 02-27-2018, 09:09 AM   #5
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The 6.5 is a good engine for longevity but does have some issues.

First, make sure the PMD has been relocated. Heat tends to burn them out.

2nd.. make sure the harmonic balancer is in good shape. With 70k miles on it, I'd replace it. These engines are notorious for breaking cranks.. and 99% of the time, it can be linked back to a worn harmonic balancer. Yup.. a ~$70 part causing complete engine failure.

Otherwise, they are good workhorse engines. They are not power houses... but they will do work for years on end as long as basic maintenance is kept up on them.

The electronic injection pump on the newer 6.5 is sem-failure prone. They aren't terribly expensive though.
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Old 02-27-2018, 09:15 AM   #6
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I knew a bus yard that was buying 6.5 buses with bad injection pumps and retrofitting one from the 6.2. The reputation I've seen for them is that the pump is the weakest spot.
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Old 02-27-2018, 10:06 AM   #7
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Gmc

So a little less reliable than the 7.3 but not a bad motor is what Iím getting from yíall. Iím a big mountain biker do you think it will hold up well with lots of mountain driving? With less power do you think it will have a significantly lower mpg? By the way yíall are awesome thanks so much for the quick responses and all the help.
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Old 02-27-2018, 10:18 AM   #8
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If you plan on lots of mountain driving, the tranny will be a really big factor. Anything that lacks full lockup will generate way too much heat going up and will not provide any braking coming down. And when paired with a smaller motor, it makes for a pretty awful mountain combo that won't last long.
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Old 02-27-2018, 10:47 AM   #9
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Dt466

What about the dt466? Would this be an efficient mountain rig or is the 7.3 my best bet? And full lock up? Sorry I donít understand
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Old 02-27-2018, 10:50 AM   #10
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Given the same transmission, a bigger motor is likely a better plan. But I'd take a 5.9 with a locking 6 speed transmission over a DT466 with at AT545 any day.
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Old 02-27-2018, 11:58 AM   #11
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Quote:
Originally Posted by Lherrlinger View Post
So a little less reliable than the 7.3 but not a bad motor is what Iím getting from yíall. Iím a big mountain biker do you think it will hold up well with lots of mountain driving? With less power do you think it will have a significantly lower mpg? By the way yíall are awesome thanks so much for the quick responses and all the help.
The 7.3 has more hp and torque than the the 6.5 but the 6.5 gets better MPG. The 4l80 trans behind the 6.5 has a lock up TC that locks in 3rd and 4th. Definitely not as HD as the Allison but plenty for a van based short bus.
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Old 02-27-2018, 01:36 PM   #12
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4l80e is a great trans and should be what is behind that 6.5

With a basic shift kit (TransGo HD2), the 4l80e can hold north of 700hp (weak link is the input shaft at that point).

As far as comparing the 6.5 to the 7.3 (powerstroke I assume..).. they both have their quirks. The 7.3 has plenty of common issues such as valve cover harnesses, fuel leaks, high pressure oil system failures (leaks, pump, etc).. but it's still a good engine.

I'd say they are pretty equal. The 7.3 has a higher power potential.. but stock for stock, they are similar. As stated, 6.5 does get better mileage.

The 6.5 is cheaper to work on due to it's injection system design. Injectors, pump, etc.. are cheaper by a good bit.
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Old 02-27-2018, 04:00 PM   #13
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The AT545 is a non-lockup transmission. That basically means there is never a mechanical connection between the engine and rear axle. Only fluid. It over spins when under a load (going up a hill) which produces excess heat (the bane of all auto trans) and will not provide any engine braking when you let off the pedal (overworking the brakes and making for a scary decent). Since mountain driving involve a lot of both up & down, this type of tranny is the poorest choice. A newer Allison that has the lock-up feature will provide much better control and survive much longer under such conditions. There are numerous models available with lock-up. I believe all the Allison 1000, 2000 & 3000 series are such but maybe someone else here can verify or expand on that. Just maybe the best place to find a Skoolie so equipped is in Colorado. Many of their buses are speced that way for just the reasons above.

Best of luck on the hunt.
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Old 02-27-2018, 05:21 PM   #14
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Don't know if it's the same but I have the 6.6 duramax in a 2001 2500 that just hit 400,000 and still runs strong even with a loaded trailer.
Over the years it has had problems but nothing major.
More like fuel lines wearing out and keeping the carbon blown out of it.
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Old 02-27-2018, 05:32 PM   #15
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Don't know if it's the same but I have the 6.6 duramax in a 2001 2500 that just hit 400,000 and still runs strong even with a loaded trailer.
Over the years it has had problems but nothing major.
More like fuel lines wearing out and keeping the carbon blown out of it.
GM kept using the 6.5l in the 2500 and 3500 vans until 2003. I wish my bus had a duramax, I have one in a 09 dually.
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Old 02-27-2018, 05:57 PM   #16
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We have had a few issues over the years as for as being picky about starting every now and then but a little gasoline(not either) will do it every time.
Either is to hard on a diesel and it usually vapor locks the motor especially after 2-3 tries on the batteries. A squirt bottle of gas is a lot softer on the motor,allows weak batteries to still turn it and does the same job.
With either one? Make sure your key switch is off and the glow plugs ain't warming up or hot and ready especially if you spray directly into the turbo verses the filter.
Please use gas instead of ether? You run less chance of cracking something.
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Old 02-27-2018, 08:15 PM   #17
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there is no real comparison between the DT466 and the 7.3 (T-444E).. your inline 6 cylion der diesels have more low end torque than the V-8s.. I own a DT-360 (mechanical) and a T-444E (navistar version of the ford 7.3).. my DT-360 is nice and torquey on the lower RPMs.. it doesnt have a lockup transmission so it lacks a bit in the hills but its in a heavier bus than my 7.3, the only reason my 7.3 outperforms my DT-360 is because the 7.3 has a lockup transmission..

a DT-466 with a lockup transmission is a great torquey rig!!

-Christopher
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