6.5 GM V8 diesel engine.....How many miles will that engine last for....!!??

[midnightman]

Father inlaw has a 96 2500 with one. Engine has been torn down and rebuilt twice. I think it’s still under 400 000km, so not a lot of miles. Still runs, but doesn’t sound quite right. Carries a 100gal fuel tank now so its longest round trip now is about 5 miles. Seeing that it probably gets less than 100miles put on a year it should last a long time 

[MeanGene1]

Operator error- I always thought it was very unreasonable and abusive to expect those pickups with 6.5's to actually pull a trailer- what were they thinking? When we were still running the 410 sprint car my buddy had a Chebbie dually to pull the trailer- it was really embarrassing to tow a sprint car at 50 mph 🤡

[vtfireman85]

I went to college with a guy who drove a 00’ classic 3500 CCDRW with 350 (a very new truck at the time). The 6.5 would have been a big improvement power wise. I always wondered why not a 454 or 6.5. In those days diesel was cheap, with the right gears, that would have been a decent truck. 

[FarmerFixEmUp]

17 minutes ago, vtfireman85 said:

I went to college with a guy who drove a 00’ classic 3500 CCDRW with 350 (a very new truck at the time). The 6.5 would have been a big improvement power wise. I always wondered why not a 454 or 6.5. In those days diesel was cheap, with the right gears, that would have been a decent truck. 

My 92 3500 with the 6.5 pulled way better than my current 1998 K2500 with the 5.7 Vortec gas. Diesel had 4.10 axle, this one has 3.73. Going up a hill hauling a tractor or something the diesel would shift down a gear or so and keep pulling. The 5.7 drops 2 or 3 gears and starts screaming 4500 or 5000 RPM. Seems like they could program that transmission not to do that. Both 4L80E transmissions. 

[vtfireman85]

9 hours ago, FarmerFixEmUp said:

My 92 3500 with the 6.5 pulled way better than my current 1998 K2500 with the 5.7 Vortec gas. Diesel had 4.10 axle, this one has 3.73. Going up a hill hauling a tractor or something the diesel would shift down a gear or so and keep pulling. The 5.7 drops 2 or 3 gears and starts screaming 4500 or 5000 RPM. Seems like they could program that transmission not to do that. Both 4L80E transmissions. 

My dad had a 5.7 4l80e in a 2001 van with 3.73 gears. It did ok, the 6.0 was an improvement, despite my trucks being ordered with lowest possible gears and his being ordered with higher ones, he acknowledges mine tow better and get similar mileage, but he continues to beat his head against a wall and orders high gear sets. 

[Pukeko]

On 6/28/2026 at 11:21 PM, mike newman said:

...looking at a single cab Sierra with the 6.5 V8    diesel engine,...its already gone 240,000 miles....The flat deck is what i like...its been converted to RHD..looks the goods..it has a price tag on it that will make you guys laugh your socks off...but that is New Zealand..but its only a 2x4.....

...however...just wondering if some of you blokes could offer a few thoughts on that particular engine's life.....if any......after 240k   miles....

TIA

Mike

dont touch it with a barge pole . Overpriced P.O.S. No parts available down there,nobody will know anything about them.They broke cranks due to harmonic balabcer breaking,blocks cracking due to poor casting,oil pump switch failing causing hard srarting problems .If an auto,probably 4L80trans ,certainly no parts or knowledgedown thereon that topic.They were replaced early 2000,s by the Isuzu  "Duramax" for good reason. Being 2 wheel drive ,heavy front end ,pisspoor off road  due to heavy front end .

[acem]

Saw an ex military blazer with the diesel on the road today.

[db1486]

Reading this sounds like 99% of 6.5's were lemons and we got the one good one in the bunch here lol. I can't complain about the service we got out of it. Other than the pump issues early on I thought they were pretty decent

[FarmerFixEmUp]

10 hours ago, db1486 said:

Reading this sounds like 99% of 6.5's were lemons and we got the one good one in the bunch here lol. I can't complain about the service we got out of it. Other than the pump issues early on I thought they were pretty decent

Guess I had another one, replaced with another used engine.The one we took out had over 300000 on it. 

[db1486]

6 hours ago, FarmerFixEmUp said:

Guess I had another one, replaced with another used engine.The one we took out had over 300000 on it. 

Original motor in dad's had 425000 km on it. Truck has around 540000 now. I have no doubt the original motor would still be running, but we swapped it due to cracked block, which was our fault, not the trucks. 

[Sask466]

They sure have a recognizable sound.  When you hear one in a parking lot, you don’t even have to look to know it’s a 6.5

[dale560]

1 hour ago, Sask466 said:

They sure have a recognizable sound.  When you hear one in a parking lot, you don’t even have to look to know it’s a 6.5

At my funeral I want a continuous tape rolling of a 5.7 diesel idling. They are a unique sound just like a 6.2/6.5 or a 6.9/7.3 ih.

the 6.2 ,6.5 weren’t that bad but not excellent. If you took care of them 100,000 miles wasn’t abnormal. The problem with most of the engines were die grinder gasket wheels if worked on. 

[dale560]

Dad bought this Kent Moore tool from ih dealer when the were closing. If you did any pump work this worked well to set timing. I could get them pretty close by ear when they idled but checked them with this all the time. It picked up pulse from injector firing and you set timing to specification with tool. I had a certain amount for lag in pulse pickup you corrected for and offset of timing probe to pointer. Snap on had a lumy mag timing tool that you screwed an adapter in glow plug hole and it picked up flame from firing. Of course snap on claimed it was best but you had a lot of issues with fuel quality and other stuff trying to time them that way. I think most the 5.7 and 6.2 were set at 4 degrees afte tdc with the kentmoore. The actual timing was probably around tdc or a bit advanced but the tool figured the pulse and magnetic pickup signal to give you that setting. Usually the pump was set 1/8 inch towards driver side from the two hash marks on pump and mount adapter. Ford was set the upposite way towards passenger side if i recall correctly. Been 20 years now since I messed with them.

[vtfireman85]

7 hours ago, dale560 said:

Dad bought this Kent Moore tool from ih dealer when the were closing. If you did any pump work this worked well to set timing. I could get them pretty close by ear when they idled but checked them with this all the time. It picked up pulse from injector firing and you set timing to specification with tool. I had a certain amount for lag in pulse pickup you corrected for and offset of timing probe to pointer. Snap on had a lumy mag timing tool that you screwed an adapter in glow plug hole and it picked up flame from firing. Of course snap on claimed it was best but you had a lot of issues with fuel quality and other stuff trying to time them that way. I think most the 5.7 and 6.2 were set at 4 degrees afte tdc with the kentmoore. The actual timing was probably around tdc or a bit advanced but the tool figured the pulse and magnetic pickup signal to give you that setting. Usually the pump was set 1/8 inch towards driver side from the two hash marks on pump and mount adapter. Ford was set the upposite way towards passenger side if i recall correctly. Been 20 years now since I messed with them.

It must take some awful funny looking wrenches to set timing on the fly on a 6.5/6.2

[jimw]

 The 6.5 I had did a better job of pulling my gooseneck than the 454 I had. I had a gravity box I would pull. Hard to beat diesel torque .  Good 80s trucks though they came out later but nothing like the Duramaxes after. 

[dale560]

2 hours ago, vtfireman85 said:

It must take some awful funny looking wrenches to set timing on the fly on a 6.5/6.2

Yes they had wrenches that were double offset. I always used a couple of set open end and one closed end wrench to turn the bottom nuts. You are not supposed to turn pump while running it can lock head and rotor but I did a lot of them that way.. here are wrenches and turning tool

[Sask466]

Remember they were a cheap option back then when new (I think 1/2 of a Cummins?), got amazing mileage and by the end were okay for reliability.  Pretty low cost of ownership motor when you look at the entire lifecycle.  And you could get them in 1/2 tons.  
 

Compare them to modern 1/2 ton dieselengines for reliability and get back to me. 
 

They were to 3/4 tons what the 3208 Cat was to tandems.
 

Best diesel ever, no.  Worst ever, certainly no!   
 

edit - I may be wrong on the 6.5 option being a lot cheaper than the Dodge or Ford diesel offerings back then.

[dale560]

2 hours ago, Sask466 said:

Remember they were a cheap option back then when new (I think 1/2 of a Cummins?), got amazing mileage and by the end were okay for reliability.  Pretty low cost of ownership motor when you look at the entire lifecycle.  And you could get them in 1/2 tons.  
 

Compare them to modern 1/2 ton dieselengines for reliability and get back to me. 
 

They were to 3/4 tons what the 3208 Cat was to tandems.
 

Best diesel ever, no.  Worst ever, certainly no!   
 

edit - I may be wrong on the 6.5 option being a lot cheaper than the Dodge or Ford diesel offerings back then.

I remember looking at a window sticker of a 1989 extended cab 6.2 with auto long box light duty 2500. The bottom line was 18900 dollars so there was some room for wiggling yet. I think the diesel option was around 3000 back then.

[vtfireman85]

9 hours ago, Sask466 said:

Compare them to modern 1/2 ton dieselengines for reliability and get back to me. 
 

They were to 3/4 tons what the 3208 Cat was to tandems.
 

Best diesel ever, no.  Worst ever, certainly no!   

Agree on the first point, but I really like the 3208, no it’s not a power house, but it starts really well cold and it gets good economy, but most of all it just doesn’t seem to give any drama. I feel like the 6.2/6.5 earned a bad reputation much like Saab did, it wasn’t that they were bad, it’s just that nobody seems to know how to fix them. 

[FarmerFixEmUp]

When I bought a trailer to haul tractors for my shop I had a 1989 GMC K2500, standard cab, 5.7 gas and a turbo 400 (no overdrive) and 4.10 axle. Did pretty well but not very efficient on gas. I looked around and found a 1990 GMC 2500 extended cab 6.2 diesel 5 speed with 3.73 axle. Told the owner I'd like to see how it pulled.  Hooked on to the trailer and went for a ride with my 706 on it. That truck had no business being in ffront of a trailer. Wouldn't pull a hill nearly as well as the 89 with the gas engine. Brought it back, told him it's a nice truck but no thanks. Later I bought my 1992 K3500 srw standard cab, 6.5 turbo 4L80 with 4.10 axles. It was a day and nught difference from the NA 6.2. Not a Cummins or 7.3 but did well. 

[Sask466]

2 hours ago, vtfireman85 said:

Agree on the first point, but I really like the 3208, no it’s not a power house, but it starts really well cold and it gets good economy, but most of all it just doesn’t seem to give any drama. I feel like the 6.2/6.5 earned a bad reputation much like Saab did, it wasn’t that they were bad, it’s just that nobody seems to know how to fix them. 

Oh I didn’t intend any disrespect to the 3208 Cat.  It had its place.  At 200hp and below - great engine.  At 275hp and 50,000lbs and drove hard … well it wasn’t a L10 Cummins or 3306 Cat.  
 

 

[vtfireman85]

6 hours ago, FarmerFixEmUp said:

When I bought a trailer to haul tractors for my shop I had a 1989 GMC K2500, standard cab, 5.7 gas and a turbo 400 (no overdrive) and 4.10 axle. Did pretty well but not very efficient on gas. I looked around and found a 1990 GMC 2500 extended cab 6.2 diesel 5 speed with 3.73 axle. Told the owner I'd like to see how it pulled.  Hooked on to the trailer and went for a ride with my 706 on it. That truck had no business being in ffront of a trailer. Wouldn't pull a hill nearly as well as the 89 with the gas engine. Brought it back, told him it's a nice truck but no thanks. Later I bought my 1992 K3500 srw standard cab, 6.5 turbo 4L89 with 4.10 axles. It was a day and nught difference from the NA 6.2. Not a Cummins or 7.3 but did well. 

That’s how my utility truck is set up, and I like it a lot.. when it runs. 
the 6.5 was the diesel option for my dad’s 01’ 2500 Savana, I was young enough to still be enamored with diesels, and I practically begged him to get it. He ended up with a 5.7, it ended up wiping out the cam bearings at 60K, it was well outside warranty,  but the dealer went to bat for him and he never saw a bill. That was the beauty of a small dealer with a good customer relationship. 

[acem]

I have an old air force box van with a diesel. Probably a 6.5.

Never started it. Bought it at a city auction and use it for a storage building. It was supposed to run and drive but I wanted it for a storage building 

[mike newman]

..thank you all for the many replies to my query, re the ubiquitous  6.5 V8  GM Diesel....

..I did detect a general theme of negativity, towards this offering from General Motors...thus I passed on the truck in question...

Trucks of that size in New Zealand  are few and far between....our offerings from the three main Japanese companies, if offered as cab /chassis, have a deck suitable for two dogs and a lunch box... anything bigger than that is subject to the same rules and inspections and road tax  and diesel tax...as the big   guys..Class   8 and beyond...

I had a neat 3 ton rice burner ...Toyota....but as it aged, it got a bit rusty  here and there...thus becomes  fodder for the  crusher....and being Toyota, it was mechanically   OK...so the motor /G box etc are exported back to some third world country....the rest scrapped... 

Bit odd considering various Socialist Govts have almost reduced NZ to third world status.....oh well..just part of the great tapestry of life....sigh

Mike