Duramax or Detroit V8 engines?

[Jonathan Ashbeck]

Originally Posted by Nlambert

But that's usually the case..... manufacturers are coming up with more technology that consistently bumps up the power ratings on diesels. The thing is..... diesels can be a lot more powerful than manufacturers let them be. With emissions laws they are trying to squeeze as much power out of the engine as they can within their safety margins while remaining within EPA regulations. A properly set up truck with a tuner will last forever. The problem is most people cannot keep their foot out of them. Anyhow, I digress.


The 6.5 was one of the worst diesel engines to find its way into a truck. There was nothing reliable about them. Dad got suckered by my cousin into trading a 99 F250 (5.4L V8) for a 95 GMC 3500 with the 6.5L in it. At 90k miles it had already been through one engine replacement. In the short time that he owned it we replaced the PMD (pump mounted driver) twice (finally relocating it out of the engine bay to reduce heat soak), oil pressure switch, lift pump, injectors, and a harmonic balancer.


The 6.5L was extremely anemic and it's best case was 215 HP/ 440 lb-ft torque. Typically you found them with 180 HP/360 lb-ft torque until the very late years. The engines were meant to be an "affordable diesel" option and weren't built with longevity in mind. Finding one that broke 300k miles was a sight to see. Rest assured it wasn't trouble free.


In case you weren't aware, here are some of the most of the common issues with that engine:


Lift pump (rough running, power loss, overworking the IP)
IP failure (no start, won't run)
Oil pressure switch (no start)
Harmonic balancer (deteriorates causing a broken crank)
Crank pulley (deteriorates causing a broken crank)
Weak block casting (cracked main webs, cracked head bolt holes, cracked cylinder bores)
Cracked heads (cracked valve bridges, head gasket failure)
Poor head gasket clamping design (head gasket failure)
Injectors (running rough, smoking, loss of power, and in extreme cases a hole in the piston)
Vacuum turbo control system ( low power, rolling black smoke, overheating, engine failure)
PMD overheat (no start, intermittent shut down while driving, all the way to engine run aways)


I would rather have 10 6.4L Powerstrokes before I would own one 6.5L. The 6.6L Duramax all in all is a good engine. A few had injector issues but GM covered those. The only other problem they suffered from years ago were water pump failures. Once GM got that handled the engines are about as reliable as you could ask for.

They also had crank failure due to their age and they had cracked cylinder heads. The Duramax 6.6 LB7 has problems of their own including injector failures and blown head gaskets just like the Detroit 6.5 and Powerstroke 6.0 In general though, the Duramax engines are reliable.

[Nlambert]

Crankshaft failure was not a common failure in the Duramax. Has it happened? More than likely yes. But it wouldn't be too difficult to find on every other brand at some point in time. That holds true for every engine.


The LB7 sees head gasket failures if it's put into high boost/pressure situations. That means someone tuned the truck without studding the heads and allowed the head to lift and the gasket fail. This is common across ALL diesel engines (including the Cummins). Head bolts are just not designed for excessive amounts of boost. You have to do some preventative upgrades (like head studs) if you intend to go that route. If you stick a turbo on a naturally aspirated gas engine it will do the same thing. When the pressure overcomes the clamping force of the head bolts the head lifts. When it lifts and the engine overheats, you can get a cracked head.


Injector failures have already been discussed. GM went through a few years with some issues and extended the warranties on the engine to cover their replacement. Injectors are a wear item on a diesel so at some point you're going to replace them.

[Jonathan Ashbeck]

^^ I wasn't saying that the Duramax had crankshaft failure. I said it was the 6.5L ENGINES that had crank failures.

[Jonathan Ashbeck]

And here's the thing, the Duramax 6.6L diesel engines. They are just as reliable as the Cummins 5.9 24v and 6.7L as well as the Powerstroke 7.3. While I still prefer the 6.5 but the 6.5L is not a reliable engine. Even I bought a truck with the 6.5, I would never carry heavy loads.

[Nlambert]

To each his own I guess.