PDA

View Full Version : GM 6.5L Diesels



BigClay
05-18-2010, 02:31 PM
I know most people prefer dodge or ford diesels, but those engines must be plated in gold for what some people want for them. So my question is this; is a 6.5L turbo diesel truck from GM with 150k+ worth buying? Opinions?

paulkeith
05-18-2010, 02:41 PM
paging cam...

ATL ZJ
05-18-2010, 02:42 PM
I'll defer to trey or matt...

BigClay
05-18-2010, 02:42 PM
I was also thinking of Overkill haha

zjeepin
05-18-2010, 03:02 PM
if you buy one be very very very very very very very very very very very very careful... then don't do it




seriously, don't waste your money. Mine was in decent shape for when i bought it with 190k on it, from 2 days after i bought it there were problems and never really trusted it completely. I upgraded everything possible when failures occurred and in the end really could have bought a much better truck for my application for the money and time i spend keeping that one on the road. my rig would be insane right now if i didn't have to spend so much money keeping the ole 6.5 going. i ended up selling the truck for next to nothing just to get it off my back.

sound similar matt?

I had upgraded heads, arp studs, heath diesel chip and turbo controller, relocated PMD, gages blah blah blah and there was always something else that needed to be worked on that cost money...

if you want more info I have researched just about every topic on those motors, you can build a 6.5 that will keep up and last but you'll easily have 6k+ in it even if you install the motor yourself. dieselplace.com is an excellent source of info on 6.5's.

my honest to god advice is stay away, pay more get a powerstroke, cummins or a late model 2500 gasser or similar. it'll be worth it, i promise. take your time shopping and educate yourself on the truck you are interested in. there are good deals out there on diesels you just have to be patient and able to snatch up a good deal when you find one.

BigClay
05-18-2010, 03:50 PM
Lookls like the 6.5 is out :)

What do you guys think about a GM 454 in a late 90s GM?

OverkillZJ
05-18-2010, 03:55 PM
I won't type to much since it looks like it's already been said! The 6.5 CAN be a great motor, but if you're jumping into it like I did with little knowledge, you'll be stranded across the country and spending enough fixing it to have bought a powerstroke, cummins, or duramax in the first place.

That was an expensive mistake.

Poser 5.9
05-18-2010, 03:56 PM
One of my old co-workers had a '98 2-wheel drive dually with 4.10 gears from the factory. He loved the truck, and it never let him down, but the milage was horrible.

zjeepin
05-18-2010, 04:06 PM
Lookls like the 6.5 is out :)

What do you guys think about a GM 454 in a late 90s GM?

454 is a good motor for towing, just plan on getting about 5mpg, hell my 6.5 got 10mpg towing!! the automatics in those trucks are really dependable too.

if you are thinking gasser look at the chevy 2500hd's with the 6.0, they are plentiful in the market, affordable and dependable at higher mileages.

what are you looking to spend on a tow rig clay?

ATL ZJ
05-18-2010, 04:47 PM
if you buy one be very very very very very very very very very very very very careful... then don't do it




seriously, don't waste your money. Mine was in decent shape for when i bought it with 190k on it, from 2 days after i bought it there were problems and never really trusted it completely. I upgraded everything possible when failures occurred and in the end really could have bought a much better truck for my application for the money and time i spend keeping that one on the road. my rig would be insane right now if i didn't have to spend so much money keeping the ole 6.5 going. i ended up selling the truck for next to nothing just to get it off my back.

sound similar matt?

I had upgraded heads, arp studs, heath diesel chip and turbo controller, relocated PMD, gages blah blah blah and there was always something else that needed to be worked on that cost money...

if you want more info I have researched just about every topic on those motors, you can build a 6.5 that will keep up and last but you'll easily have 6k+ in it even if you install the motor yourself. dieselplace.com is an excellent source of info on 6.5's.

my honest to god advice is stay away, pay more get a powerstroke, cummins or a late model 2500 gasser or similar. it'll be worth it, i promise. take your time shopping and educate yourself on the truck you are interested in. there are good deals out there on diesels you just have to be patient and able to snatch up a good deal when you find one.


for those that don't know the backstory, that truck was the c2500 that I used to have... I think I got the last bit of reliable life out of it before Trey took it over. And I use the word reliability loosely. I had to put a new range fork in the tcase, replaced a couple slave cylinders, clutch lines, did the whole exhaust after finding my cat was clogged and preventing the turbo from building any boost, etc.

I'm pretty sure that if I hadn't sold it to a friend the buyer would have come after me with a shotgun because it literally broke on the drive home. Even after the truck was "fixed" the nightmare continued...

You'll pay for your savings on a cheap tow rig in blood, sweat and tears. Even on a moderate budget, there are better trucks out there than the 6.5s. An older cummins or powerstroke or even a newer chevy 1500/2500 with a 5.3/6.0 will be fine to pull your rig around the southeast.

carcrafter22
05-18-2010, 09:07 PM
Do yourself a favor and forget about the 6.5. If you want something similar weight on the cheap look at an isuzu 4bd1t they make great power regularly go 350,000 miles in 15,000+ pound loaded trucks with daily abuse and can be had from $300-$1500 all day long in excellent condition.

I dont care what you do to a 6.5 they r junk!

BigClay
05-18-2010, 09:24 PM
what are you looking to spend on a tow rig clay?

$6,500 is my budget. I am also looking for a 4x4, so I am kinda limiting myself to mid to early 90s cummins and powerstrokes with 200k plus miles



You'll pay for your savings on a cheap tow rig in blood, sweat and tears. Even on a moderate budget, there are better trucks out there than the 6.5s. An older cummins or powerstroke or even a newer chevy 1500/2500 with a 5.3/6.0 will be fine to pull your rig around the southeast.

I have seen some 6.0s with over 150k miles, do you think that would be ok?


Do yourself a favor and forget about the 6.5.

I dont care what you do to a 6.5 they r junk!

Forgetting about the 6.5 now :D

ATL ZJ
05-18-2010, 09:49 PM
I have seen some 6.0s with over 150k miles, do you think that would be ok?


Mileage is more relevant than year although the older ones had iron heads rather than aluminum. That said, 150k on a 6.0 is just getting broken in. GM designed them to last for 300-400k if properly maintained. In my motor searching I ran across a lot of takeouts on car-part.com that had over 300k where the yard said "runs good". for what it's worth...

BigClay
05-19-2010, 09:03 AM
Thanks Cam, I will include the 6.0s in my search as well.

paulkeith
05-19-2010, 09:28 AM
http://atlanta.craigslist.org/nat/cto/1735992323.html

+ built tranny&tc + home fab flatbed, done and done.

1fox2go
05-19-2010, 09:57 AM
My old man still has his truck. Did you call him? Maybe you guys can work something out

BigClay
05-19-2010, 10:00 AM
Thanks for the link, just wish it was closer.

zjeepin
05-19-2010, 10:09 AM
http://asheville.craigslist.org/cto/1729477141.html

spend your extra 3k on body work and mods and you'll have one hell of a truck

or http://asheville.craigslist.org/cto/1720063465.html. i know of lots of trucks like these that go 3 or 400k when well maintenanced...

http://asheville.craigslist.org/cto/1702530946.html

paulkeith
05-19-2010, 12:34 PM
Condition depending that '97 looks like it could be a helluva buy.

zjeepin
05-19-2010, 01:04 PM
Condition depending that '97 looks like it could be a helluva buy.

(both fords i posted links to are 97's):tease:

those are really good trucks in general, the ttb rides really smooth and the 7.3 is pretty much bullet proof with tons of aftermarket.

what do you think clay?

bshows73
05-19-2010, 01:15 PM
I have a 97 powerstroke F-350 and love it. Do yourself a favor if you get a 350 it will have a live front axle Dana 60. Spend the $400 on a shackle reversal for the front makes them handle so much better. They always leak around the fuel bowl from the older o-rings. Other than that routine maintenance and a Tranny down the road and you are good to go. Mine has 125,000 my parents bought it brand new and I bought it from them about a year ago.


(both fords i posted links to are 97's):tease:

those are really good trucks in general, the ttb rides really smooth and the 7.3 is pretty much bullet proof with tons of aftermarket.

what do you think clay?

BigClay
05-19-2010, 01:38 PM
what do you think clay?


I am going to call the guy tonight about the blue extended cab ford. Rust is the only thing that makes me apprehensive, I wonder how bad it is.

zjeepin
05-19-2010, 01:53 PM
well, there is a hole rusted in the front bumper now that i look closer but it is a good price for the truck.

if you think you are interested after talking let me know, i work in arden, i could possibly get together with the guy and take a look at it to save you the drive down here..FWIW

BigClay
05-19-2010, 01:55 PM
if you think you are interested after talking let me know, i work in arden, i could possibly get together with the guy and take a look at it to save you the drive down here..FWIW

Thanks Trey, I might take you up on that.

BigClay
05-19-2010, 03:20 PM
Well the blue F250 has already been sold... dang

zjeepin
05-19-2010, 04:32 PM
good deals don't last long usually...

BLK97ZJ
05-19-2010, 10:20 PM
I just picked up a 97 suburban 2500 6.5 with 120k And i love it. It had the injection pump done 6k miles ago. Its in really nice shape. I just did heath stage 2 and couldn't be happier with the amount that I've spent.

zjeepin
05-20-2010, 07:39 AM
I just picked up a 97 suburban 2500 6.5 with 120k And i love it. It had the injection pump done 6k miles ago. Its in really nice shape. I just did heath stage 2 and couldn't be happier with the amount that I've spent.

best of luck to you with that truck, there are guys that swear by the 6.5 and there were times that I was really happy with mine, then something else would go wrong... go ahead and do the dual thermostat upgrade and hi flow water pump, the last thing you want is that engine getting hot. and too hot is 210 or above, you should probably find yourself a set of new injectors too as their service life is 100k before they start to mess with engine timing.

have you towed your jeep with it yet?

BigClay
05-20-2010, 11:01 AM
Going to look at a 91.5 Cummins tomorrow. Anyone know what the mid year changes were? Any advice or opinions on this body and motor?

1fox2go
05-20-2010, 11:48 AM
Ive never heard of a 91.5 only the 98.5 which is when they went from 12 valve to 24 valve and the 04.5 which I do not know all the changes.

Those older body styles have thicker sheet metal than the newer trucks. The autos were top notch. Performance wise they are grunts, turn up the fuel and tweak the boost and you are good to go.

Ahhh. Perhaps that .5 year could be the year they started to intercool them...

If its intercooled find out if its factory or someone added it.

BigClay
05-20-2010, 12:02 PM
Yep, I just did a google search and mid year 91 is when they put an intercooler in the Cummins.

For a diesel newb, is the intercooler for the turbo?

This truck is an auto, so the autos are OK in these years?

paulkeith
05-20-2010, 12:47 PM
baha! diesel newb! everyone point! :D.....jk


When the turbo compresses the incoming air, it heats it up (charles's law). If your setup is intercooled, the hot charge air then enters the intercooler and gets cooled down, usually a pretty appreciable amount, before it goes into the engine. The intercooler is basically an air to air heat exchanger. Charge air inside, ambient airflow outside. Cooler air= denser air = more HP. Its *technically* an aftercooler since it cools the air after the compression, but meh. This also helps control EGTs if the air starts off cooler.

The basic beauty of diesels is that the more air (larger or faster spool on turbo) and fuel (fueling mods) you can cram in, the more horsepower they make, practically linearly, to limits of EGT, head stud, and bottom end strength. The motors themselves are usually detuned for longevity so they're strong enough to take pretty decent mods with no large adverse effects.

quick pic:

http://www.aa1car.com/library/turbo_schematic.gif

as in that pic, you'll see them often referred to as the charge air cooler, CAC, etc. I think this might be what Dodge/Ford/Chevy actually call them.

1fox2go
05-20-2010, 01:17 PM
Yea the autos were pretty good. My dads is still holding strong. Find an oil pan off a newer dodge to put on the older and it will hold more trans fluid. 2 quarts I think he said.

BigClay
05-20-2010, 01:38 PM
haha, thanks paul!

Well looks like if this one is in decent shape it might be a keeper.

zjeepin
05-20-2010, 02:07 PM
haha, thanks paul!

Well looks like if this one is in decent shape it might be a keeper.

cool, glad you've got a good prospect. 12v cummins are hard to beat, simple and tough, cheap and easy to modify.

do you know how many miles?

I've heard from several cummins gurus that if the serp belt doesn't give a little chirp when you shut the motor off that compression is beginning to deteriorate. whats happening is the motor stops turning faster than the accessories being driven by the belt can stop so you get a short and sharp squeak and if you pay attention, most cummins do make that sound at shutoff. FWIW

BigClay
05-20-2010, 02:17 PM
Great info Trey, I will definitely listen for that. This one has a little over 200k on the odo.

BigClay
05-20-2010, 02:19 PM
I have someone on my local forum telling me that this year cummins/tranny has a hard time towing 7k without turning 3k RPMs, anyone on here heard the same?

zjeepin
05-20-2010, 02:54 PM
sean (s10 seanzy) on here tows with a 93 (i believe) and he recently did at 5 speed swap in his for that reason but he didn't turn the fuel up on his until after the 5 speed swap.. lets see if we can get him to chime in on this one

Pearce
05-20-2010, 02:58 PM
That can depend on the axle gearing too, if it has 4.10's then yeah it might be running high RPMs. If I remember right the sweet spot tends to be around 2000 give or take a few hundred depending on engine year. For me its about 1800.
But I've never heard of a good Dodge auto tranny till the more recent models. I've got the 04.5 and it's huge improvement to the previous. The newer ones are even better. But I still have the 1 to 2 shift hunt from time to time even. There is a TSB to fix it, but I'm out of warranty and can live with it for now, 111,000 miles on it.

BigClay
05-20-2010, 03:28 PM
It is looking like the manual is the way to go, so I am still on the hunt...

zjeepin
05-20-2010, 03:32 PM
It is looking like the manual is the way to go, so I am still on the hunt...

you should try to find out what axle gearing the truck you are looking at has, it will make a big difference in running speed rpms, tire size makes a difference too...

depending on how clean the truck is you may be able to read the tag on the rear diff. do some research on the trans gearing and put it all in a gear calculator to see what rpm's you'll be running..

1fox2go
05-20-2010, 05:03 PM
That can depend on the axle gearing too, if it has 4.10's then yeah it might be running high RPMs. If I remember right the sweet spot tends to be around 2000 give or take a few hundred depending on engine year. For me its about 1800.
But I've never heard of a good Dodge auto tranny till the more recent models. I've got the 04.5 and it's huge improvement to the previous. The newer ones are even better. But I still have the 1 to 2 shift hunt from time to time even. There is a TSB to fix it, but I'm out of warranty and can live with it for now, 111,000 miles on it.

Im going to argue with you on this since I hear the stories and help my dad put in the transmissions. The older ones we have yet to have to replace an auto trans. The newer ones are junk and he does at least 2 a week. Many with just over 100k miles on the ticker

The older cummins arent like the 24Vs, they dont turn high RPMs and they arent as quick either. But they are solid and dependable. Dont crowd them and try to get to where you are going in a hurry. My dads has the auto with 3.07 ratio. It pulls a trailer at 65-70 MPH at around 1600-1800 RPM. I would say if it is geared low it would be turning high RPMs and I would shy away from it most likely being the owner installed them theirself. Also for what its worth these trucks non intercooled will pull 7k no problem. A friend of ours hauls round bales of hay on a 30 foot trailer. 1500 lbs a bale, 8lbs of trailer with no issues.

Pearce
05-20-2010, 06:05 PM
Im going to argue with you on this since .

I'm not going to argue with you. :flipoff2: But I can disagree.

S-10 Seanzy
05-20-2010, 06:15 PM
cool, glad you've got a good prospect. 12v cummins are hard to beat, simple and tough, cheap and easy to modify.

do you know how many miles?

I've heard from several cummins gurus that if the serp belt doesn't give a little chirp when you shut the motor off that compression is beginning to deteriorate. whats happening is the motor stops turning faster than the accessories being driven by the belt can stop so you get a short and sharp squeak and if you pay attention, most cummins do make that sound at shutoff. FWIWNot really true dude. I think that is just a belt issue. Mine used to do it...I put a new belt on it and it stopped. It will still chirp every now and then on shutdown, but not often.


sean (s10 seanzy) on here tows with a 93 (i believe) and he recently did at 5 speed swap in his for that reason but he didn't turn the fuel up on his until after the 5 speed swap.. lets see if we can get him to chime in on this one

My truck is a 90 model Trey. They changed a few things on the 91.5...as mentioned before, they added an intercooler. The head design is the same aside from a different injector bore. Non intercooled injectors will make more power as they flow more. They also changed the grill up a bit. They made an absolutely hideous truck look marginally better with this grill:flipoff2:. There are a few other little things different as well, but not worth discussing.

These trucks had two different auto setups. In the early years, they had the TF727 which was the 3 spd. Mine had the TF518 which is basically the 727 with an overdrive unit behind it. They are just like any other auto. Heat will destroy it. Keep it cool and it should treat you right. Any automatic will need rebuilt eventually, when used like we use them. My truck had 180,000 on it when I bought it. The previous owner had the tranny rebuilt at 140k. It did fine while it was in my truck.

I swapped it out a little over a year ago for a Getrag 5 spd. This was the only manual transmission put behind 1st gen 12v trucks. It has its little quirks which you have to keep in mind while driving it. First, do not lug on it hard in 4th or 5th...especially when towing. They will growl at you if they don't like how you are driving it. It's hard to avoid lugging on it a completely because of turbo lag. The turbo lag can be combated by putting a smaller exhaust housing on the turbo, but this raises the egts. The Getrag also needs to be overfilled by at least a quart with only 5w-30 motor oil(preferably synthetic). Anybody that says to use anything else is an idiot. This is what it calls for and they will not survive with anything else in them. You can't speed shift the Rag. It goes in gear when it wants to. If the shifter is vibrating badly or popping out of gear then it is in desperate need of a rebuild.

I have someone on my local forum telling me that this year cummins/tranny has a hard time towing 7k without turning 3k RPMs, anyone on here heard the same?
A stock 12v will not even turn 3k rpms. They are governed at 2750. You can buy an aftermarket governor spring for the injection pump that will raise it to 3200. Being a 91.5, it likely has the 518. The gearing in it is likely 3.55. This was the most common gearset used. 3.07s were only used in trucks with the 727. And 4.10s were only used in 4wd trucks. I never had a problem towing with the auto. The only thing that I ever noticed while towing, is that it didn't like to shift into overdrive until I let off the gas pedal about halfway. This can be quite the pain in the ass when trying to keep you momentum on a hill. This was part of the reason for switching to the 5 spd. I think you just have much more control over your load when using the manual. The load that I pull is probably between 7k and 8k. I haved towed around 10k with the auto no problem though.

Overall, the 1st gens are a tank of a truck. The balljoints on the 2wds suck. Just take care of either tranny and you'll be ok. One thing to look for on the engine. When the head gasket starts to go, they will leak antifreeze at the front of the engine where it meets the block, just under the thermostat housing. I love my truck...it has been the best damn vehicle that I have owned to date. I don't think you can go wrong if the price is good and you look over some of these things.