LLY Overheating: The GM Solution and Beyond - 4

Volume 1 Issue 3 - Diesel Articles

Article Index
LLY Overheating: The GM Solution and Beyond
Exploring Solutions
LLY Underhood Airflow
Aftermarket Solution?
The GM Solution
Facing the Killer
Killer Hill Vanquished
All Pages

Considering an Aftermarket Solution

Now, consider how poorly the radiator works when the air running through it is much hotter than the outside air. This feedback loop leads to the runaway overheating condition that I had experienced on Killer Hill. When this revelation finally got through to me, I went right over to a Duramax and had a close look. I could clearly see how this problem could happen just by looking at

the intake and the intercooler system. The solution became quite simple in my mind: get a cold-air intake. It seemed clear to me that someone at GM had dropped the ball when they installed an underhood warm-air intake in these trucks.

I considered using an off-the-shelf aftermarket cold-air intake; but there is a need to be choosy here as well. One concern with many aftermarket intakes is their cold-air effectiveness. Most do have a baffle which somewhat shields the air filter from underhood air, which is desirable. But for the LLY we wanted complete – not partial – isolation to stop the runaway thermal feedback problem. That left me with two options: Bank’s Ram-Air system or Volant’s cold air intake. Both are completely sealed from the engine bay and have the option of providing a cold air ram scoop. However, there was another concern that made me hesitate: dust.

duramax-lly-overheating-dust-1 duramax-lly-overheating-dust-2

Dust is a mortal enemy of the piston rings and of the leading edge of the turbocharger compressor wheel. Some aftermarket intake systems can allow, in my opinion, too much dust through. Most if not all cotton/gauze/foam-oiled type air filters are not fine enough. With the aftermarket filter only catching the larger particles, most smaller particles pass through easily. In contrast, this is not a problem with the stock paper filter – it has more filter surface area and a finer filtering ability than the cotton/gauze/foam-oil varieties.

Air filters, in themselves, could provide a lengthy discussion for another article, but let me sum up with a couple of pictures. For me, the evidence becomes quite obvious by visually inspecting the air intake. In the stock intake duct (pictured, above left), there is virtually no dust after many miles (90,000) of service. The only dust present is a very light, thin film that barely rubs off with a swipe of a finger.

However, the unnamed aftermarket intake (pictured, above right) leaves a heavy film of dust on the sidewalls of the intake duct. The dust is also evident when inspecting a turbo compressor wheel: visible wear and sandblasting on the leading edge of the vanes. This may not be as evident with trucks used primarily on the highway, but it is a significant concern with trucks used on dusty, dirty roads.

That turned me to thinking about fabricating my own cold-air intake with the stock air filter. I used a lower airbox from a new-style 2007 GMC Sierra gas truck. It fits the Duramax air filter, and it will fit the classic style trucks. They have larger openings and a large foam seal that sits tight to the fender well. Letting in air from the fender well on a Duramax requires removing or cutting the seal over the holes from the factory. I opened both of these to allow cold air into the system, but there was one problem with this: the openings in the fender are not nearly large enough to feed the air-hungry Duramax. My air filter restriction gauge typically showed 50 to 80 percent restriction with a brand-new air filter. So, the easy, almost-free method was not feasible.


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