LLY Overheating: The GM Solution and Beyond - 2

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

Exploring Solutions

I was already aware of a GM service bulletin (06-06-04-036D) addressing overheating in extremely hot ambient temperatures. The bulletin applied to all 2004 and 2005 LLY Duramax engines. GM’s solution retrofits the new-style LBZ air intake to the LLY engine. I had a difficult time getting my mind around how a change in intake systems would solve an overheating issue. As a result, I did not pay much attention to the bulletin. Instead, I spent my time examining the airflow over the cooling stack: the A/C condenser, intercooler and radiator. The configuration seemed quite restrictive to me, especially the intercooler. I wondered how the radiator could ever receive adequate airflow to do its job. I also put some thought into how close the fan was to the engine. The airflow would have to take quite a turn at that point after it was pulled through the radiator. I was starting to believe that the whole problem was caused by poorly designed airflow over the cooling stack. I had begun to map out an air-to-liquid intercooler – intending to remove the factory air-to-air unit and substitute a liquid heat exchanger – that would allow better airflow in the cooling stack. Of course this would have required a serious engineering effort unto itself: a large capacity air-to-liquid unit that would handle the DMax massive airflow and heat rejection requirements, an additional liquid radiator, electric coolant pumps, thermostatic controls, all the fabricating and plumbing and so on. An expensive, complex, and highly experimental solution which may have only helped improve airflow over the cooling stack and little else.

Being a GM technician, their proposed solution lingered in my mind. As skeptical as I was about it resolving the overheating problem, it was obvious that the engineers had spent considerable time designing the new intake system. The LBZ air intake offers a much better design than the older LLY. This is true for a couple of reasons. First, the air filter proved itself to have higher capacity, lasting much longer on our dusty oil field roads than its LLY predecessor. Secondly, and most importantly, the LBZ design is a true cold-air intake system. Any hotrodder worth his salt knows that a cold-air intake is an absolute must for optimal performance; but this truth applies not only to hotrodders. For this reason alone, I was considering building or purchasing an aftermarket cold-air intake system. To understand the significance of a cold-air intake, it is crucial to understand the affect that cold air has on the turbo. Colder air means higher density air; this denser air “helps” the turbocharger – and the entire engine – by allowing it not to work as hard at its task of compressing the air before sending it on to the engine.. The turbocharger works more efficiently (meaning less power taken away from the engine) and with less heat.

I started digging into some of the Internet forums and found that the overheating issue is quite a subject for debate. In fact, I began to wonder if research on the Internet would yield any useful information. Fortunately, I did run across a Michael Patton article (these were pre-maxxTORQUE days) called Thermal Feedback Loops in Turbocharger Applications that piqued my interest. And yes, it was as fun to read as it sounds. It sought to explain how a proper cold-air intake system could potentially solve the Duramax overheating issue. I was intrigued. GM engineers certainly seemed to agree according to the service bulletin that they provided. I downloaded the article. As it turns out, the problem was not all that difficult to understand. In fact, it should have been obvious to me just by looking at the air intake system. To be fair, extraordinary effort was required (on Michael Patton’s part) to figure out the source of the problem in the first place.

I want to consider an example from the world of sound to illustrate what happens with the LLY under-hood “warm” air intake. Almost everyone has heard feedback from a sound system and “squeal” when someone turns the gain on a microphone too high. The reason for the feedback is simple: when the microphone hears sound, it feeds that sound into the amplification system. If it happens to hear sound coming from the speakers at a high enough level, it sends that sound back into the system only to be amplified more. That sound then is reproduced by the speakers at a higher volume, allowing the microphone to hear it at that louder level only to send it into the amplification system again. This happens in a very fast cycle until you hear the characteristic squealing noise or “feedback”. And then it takes very little time for the noise to drive everyone crazy. That is the essence of feedback: when something generated by a system gets re-introduced into that system and is made more intense by the operation of the system. In the case of a sound system – as with the LLY overheating issue – this effect causes a very undesirable result.


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