Weblog - Duramax Diesel

I often am asked the question, which is the best Duramax diesel to buy? I usually provide a range of answers, based on the strengths of the various Duramax engines. Here is a quick run-down of the strong points of each generation of Duramax diesel:

Top Duramax Diesel for Fuel Economy

This one is easy – the original LB7 Duramax. It's produces the best fuel economy of any of the Duramax engines. The big question is: why? Well, that gets a bit complicated to answer, but suffice to say that there are 2 major reasons. Firstly the conventional wastegated turbocharger on the LB7 allows free-breathing under light to mild loads, whereas the VVT turbocharger on the newer engines seems to require more drive pressure, robbing the engine of some efficiency. Secondly, the compression ratio of the newer Duramax engines has been lowered in an attempt to help control NOx emissions.

So why don't I drive an LB7? Firstly, I can tune the newer engines with EFILive to produce similar fuel economy numbers as the LB7. Secondly, the LB7 has old-school 15 second glow plugs which I find an annoyance. Also, living in a cold-climate, I appreciate the automated high idle in the newer engines. Thirdly, although injector reliability has been improved, I'm still not keen on buying a used LB7 with the possibility that there has already been some injector damage done.

Top Duramax Diesel for Power

The LBZ/LMM series Duramax has definitely the best power potential. With a much stronger torque curve that comes in lower, higher capacity turbochargers, and beefy engine internals, these Duramax engines produce the power. Because they are teamed with the even stronger 6-speed Allison, there is also more headroom to crank big power out of these engines with tuning. I am still amazed at how much I can get out of these things and still run relatively safe.

Top Duramax Diesel for Reliability

The prize for this definitely goes to the LBZ Duramax. All the generations of the Duramax have had various service issues, but the LBZ has the least and the most painless problems of the bunch. LBZ's that were produced after December, 2005 are particularly desirable because they have the newer design head-gaskets - the earlier head gaskets can be prone to failure. The LBZ engine also has very robust fuel injectors, able to take a kicking and keep going like no other Duramax prior. And the LBZ has all of the cooling system upgrades that make a real difference towing.

Best All-Around Duramax

It is hard to beat the all-around performance of the LBZ Duramax. Power to spare, decent fuel economy, and good reliability all contribute to making this an all-star performer. With a good power program, it can produce 460hp safely and still return 20+mpg in fuel economy when driven intelligently.

Another factor that is becoming more important to me is comfort. The LBZ is much quieter and smoother than any previous Duramax. With the 6-speed Allison, they just idle happily down the road with little fuss, and respond dramatically when you put your foot down.

So Why Do I Drive a Duramax LLY?

I haven't found reason to sell my truck yet. Once the typical service issues are sorted out, it is a strong and reliable runner. And it is probably the best behaved Duramax in extreme cold weather, starting at temperatures that put Ford and Dodge to shame. It produces good power and fuel economy when tuned, but doesn't have quite the room for power that the LBZ has. Yes, I do want an LBZ eventually, but I can work with the LLY that I have now. So what repair work have I done to my Duramax?

• Replaced turbocharger. The new one should be quite reliable with the complete LBZ intake upgrade that I did. (see Summer 2008 maxxTORQUE)
• Replaced head gaskets. The head gaskets are the new design from GM, so they should be reliable enough. I did install ARP head studs for insurance.
• Replaced #2 and #7 injector connectors. These injector connectors were notorious for having terminal issues, causing the engine to run in limp mode. I replaced them with the new design connectors, so that problem is solved.

Those are the major service issues that I addressed with my Duramax, and are common to many LLY engines. If you own an LLY, you may not ever have to address any of these issues depending on your usage. If you use your truck like mine (see YouTube video) you may need to beef things up a bit.

However, I can't help but have a little envy for all you Duramax LBZ owners. You have one you can be proud of owning, in my opinion, the best Duramax diesel ever!

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