The LBZ Duramax is, still today, the favorite Duramax of diesel enthusiasts. Produced from 2006 to 2007, the shortest production Duramax, the LBZ produced 360hp and 650lb-ft. of torque. To support the power increase over the LLY model, the block was improved, the rods were forged, and the engine was overall built to withstand more power. Because of this, the LBZ is a favorite amongst diesel enthusiasts because of its bolt-on mod performance capabilities.
When you couple the performance potential with the reliability, and lack of emissions regulating systems, it’s no wonder the LBZ is still the fan favorite over 13 years since its discontinuation. The engine was phased out in 2007 solely for the purpose of emissions regulations. Overall, the Duramax LBZ is an awesome engine that is highly reliable and capable from a performance perspective.
However, the LBZ’s on the road today are getting up there in age and likely mileage as well so it’s important to consider the common LBZ engine problems prior to purchasing one.
The LBZ and this engine problem guide are applicable to the following Duramax Chevy/GMC vehicles from 2006 to 2007:
- Chevy Silverado HD 2500 & 3500
- GMC Sierra HD 2500 & 3500
- Chevy Kodiak
- GMC TopKick
5 Most Common LBZ Duramax 6.6L Engine Problems
- Cracked Pistons
- Water Pump Failure
- Glow Plug Failure
- Transmission Line Leaks
- EGR Valve Failure
1. LBZ Cracked Pistons
The LBZ is revered for its tune-only performance capabilities. With various upgrades, this engine is easily capable of producing over 600whp and 1,000lb-ft. of torque. However, one common failure point on tuned LBZ’s is cracked pistons.
This “common problem” is really only common for folks pushing serious power. The pistons on the LBZ are generally good up until around 600whp, levels beyond that are when piston failure becomes imminent. If you plan on keeping your engine purely stock, you can ignore this problem. While the pistons have cracked before on totally stock engines, it’s highly unlikely and rare.
Duramax strengthened the block and lower half of the LBZ to handle to stock performance increases over the previous LLY models. However, the pistons remained the same, produced purely from cast iron which is why they are prone to cracking at serious power levels.
I will note that running a tune-only probably isn’t going to crack your pistons but it will obviously make it more likely to happen as any power increases will put additional stress on the engine internals.
Cracked Piston Prevention Options
If you are looking to produce serious power, you’ll need to open your wallet. And your engine. To prevent piston failure, your only option is to either not tune your LBZ or to upgrade the pistons and probably the rods to something forged.
2. Duramax LBZ Water Pump Failure
The water pump on any vehicle generally functions the same way. The pump is responsible for pushing the engine coolant throughout the cooling system to prevent the engine from overheating. On the LBZ, and all Duramax engines for that matter, the impeller inside the water pump is made of plastic. The impeller is like a little rotating fan that is responsible for actually forcing the coolant through the system.
If your impeller breaks or goes bad, the coolant won’t flow through the engine. On the Duramax LBZ water pump the impeller is made of plastic. This is actually very common on a lot of engines and is usually the #1 reason water pumps break. Over time the impeller is subject to a lot of normal wear and tear and high temperatures. For no fault other than the plastic, the impeller wears down and eventually fails.
At some point in 2006 (in the LLY Duramax model) the water pump was changed from a cast iron impeller to a plastic one. All engines from that date on, including the LBZ, are very prone to frequent water pump failure. LBZ water pumps are known to fail every approx. 80,000 to 100,000 miles.
Duramax Water Pump Failure Symptoms
- Engine overheating
- Leaking engine coolant
- Frequent low coolant warnings / refills
- Water pump is making weird squeaking noises
- Steam coming from the radiator
Water Pump Replacement Options
Solving this issue is generally pretty simple. If you continue to replace your water pump with an OEM pump that has the plastic impeller, expect to continue replacing it every 80k-100k miles. Alternatively, you could upgrade to an aftermarket pump that has a billet/aluminum/iron/etc. impeller on it to guarantee that you won’t have to be replacing it again anytime soon.
Aftermarket pumps are probably an extra $50-$100 but the replacement cost is the same and the added reliability is totally worth it in my opinion.
3. Glow Plug Failure – LBZ
For non-diesel owners, you might be wondering “what is a glow plug?”. Due to the size and the mass of diesel engines, they absorb massive amounts of heat in colder temperatures. This absorption of heat can make it very difficult to start a diesel engine in cold weather as the lack of heat prevents ignition. Enter glow plugs.
Glow plugs sit within each cylinder of a diesel engine and have a metal “tip” at the end of them. During the ignition process, the tip of the glow plugs are provided electrical current to create heat within the cylinder. The fuel injectors then spray fuel directly onto the tip of the glow plug which ignites the fuel, creating ignition when the engine is normally not warm enough itself.
In 2006 year models, both the LLY and LBZ Duramax engines had glow plug failure issues. The glow plugs are powered by a glow plug control module which sends the electrical current to heat them up. 2006 year models had a control module issue in which the module was known to overload the plugs with current, causing the tips of the glow plugs to actually break off. If the tip breaks off, you now have a piece of metal flying through your engine.
As you can imagine, this problem could cause significant engine damage.
Glow Plug Control Module Fix
Fortunately, this problem was caused by the programming of the control module. Fixing this issue was as simple as having your dealership reprogram the control module. While this issue was common in 2006 LBZ models, if you are considering buying one today this shouldn’t be of any concern as the problem was fixed long ago. Simply confirm that the module had been reprogrammed back in the day.
If you are replacing your glow plugs for any reason, here is a helpful DIY: https://www.thetruckstop.us/forum/threads/lbz-glow-plug-replacement.21280/
Glow Plug Failure Symptoms
If you have the issue with the control module, you probably won’t be running into many of these symptoms. However, I wanted to provide some common symptoms of normal glow plug failure. Glow plugs are pretty cheap and easy to replace so I recommend refreshing with a new set if you have any of these symptoms:
- Hard starting / difficulty starting (especially in cold weather)
- Rough idling
- Cylinder misfires
- Glow plug engine light
- Black smoke coming from the exhaust
4. Allison 1000 Transmission Line Leaks
While the Allison 1000 transmission is one of the best diesel transmissions out there, the tranny cooler lines used by GM had some design flaws. The cooler lines are responsible for circulating transmission coolant to keep the tranny from overheating which is important for reliability and longevity.
The lines on the Duramax LBZ have a design fault at the “crimp” to where the crimp isn’t suitable enough to hold onto the line and prevent fluid from leaking. Leaks are most common when the fluid is cold and on trucks running high idles. Some folks have a consistent leak while others tend to only leak when the engine is cold.
Fluid leaks are important to catch early as running low on fluid can cause catastrophic damage to the transmission. If you are leaking you will notice red fluid dripping from underneath the engine bay. This issue is extremely common and can occur as frequently as every 20,000-30,000 miles. There are plenty of owners who have experienced this issue within their first 20,000 miles of ownership who then continue to experience it every additional 20k-30k miles.
The best replacement options here are to upgrade to more durable aftermarket transmission lines.
5. Duramax EGR Problems
Since puffing black smoke out of your exhaust is frowned upon nowadays, diesel engines have undergone some serious emissions transformations over the last decade. While the LBZ is one of the last engines lacking serious emissions regulation systems it was still equipped with an Exhaust Gas Re-circulation system, known as an EGR.
The most common EGR issues are caused by the EGR valve. EGR essentially recirculates exhaust gases back through the engine to reburn the gas and reduce the amount of nitrogen oxide leaving the vehicle. The valve is responsible for controlling the re-circulation, essentially determining when the gas should be let out of the exhaust or sent back to the engine.
When the exhaust gases pass through the EGR valve they are carrying more than just carbon dioxide. They are also carrying particulates and other “gunk” which can get lodged in the EGR valve and cause the valve to no longer function properly. When the EGR valve becomes gunked up or clogged, it restricts the amount of airflow which then enters the engine, altering air to fuel ratios. The valve can also become stuck closed or stuck open which is what can cause significant performance issues.
Failing Diesel EGR Valve Symptoms
- Rough idle
- Sluggish performance
- Cylinder misfires
- Engine stalls while idling
- CEL for EGR or lean/rich AFR codes
- (P0401, P0404, P1404, P0405)
A lot of LBZ owners will essentially block out or delete the EGR itself. Completely removing the EGR is going to be slightly more expensive and complicated than blocking it. Either option should be sufficient in solving these problems. Blocking or removing it will remove the recirculation of exhaust gases which will prevent the gunk and particulate buildup in the EGR valve and intake manifold which is what primarily causes EGR problems. You will get CEL’s for doing either of these but they can be coded out with a tuner.
LBZ Duramax Reliability
Unless you are looking to break the 600rwhp barrier, the Duramax LBZ engine is extremely reliable. The tune-only power capabilities combined with its reliability are what make the LBZ the most sought after Duramax today, nearly 14 years after it stopped production.
With a strengthened block and good internals, the LBZ is easily capable of surpassing the 300,000 mile mark with sufficient maintenance and care.
Throughout the course of ownership you’ll probably have to replace a water pump or two and upgrade your transmission lines. Outside of these small things, you’re really only left with standard maintenance. These are really the only two common problems I would consider these engines to have as pistons are only a problem at high HP, the glow plug module should have been fixed, and the EGR can be deleted to remove any potential problems there.
One other worthwhile reliability factor to mention is the Allison 1000 transmission itself. Great transmission, however, it is only capable of handling an additional ~100hp or so before it will need to be upgraded and rebuilt. Just something to consider if you are intending on dropping more than a tune and a few bolt-ons onto the LBZ.