LLY Overheating: The GM Solution and Beyond - 6

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

Facing the Killer

There is something tangible about the character of Killer Hill. People remember it, even though they may not be aware of my nickname for it. Maybe it is the solitude of the remote location. There are no full time human inhabitants, just a seasonal lodge about five miles southeast of the top. Cell phones do not work, period. Even the wildlife seems scarce in this area of the Canadian Rockies. Vast glaciers occupy the gaps in the mountain range; their unpredictable crevasses have claimed the lives of several adventurers. Imposing towers of granite surround the narrow valleys and there are crystal blue glacier-fed lakes and snow-covered mountain meadows. I can not imagine anyone not being awe-inspired, if not fear-inspired, by the grandeur of these mountains and valleys. Killer Hill itself climbs to Bow Summit, located on the famous Jasper-Banff highway (also known as the Icefields Parkway) that spans two national parks. Though remote, the highway is a well-traveled tourist route during the Summer. In the Winter, the area is deserted due to extreme weather conditions. In the Spring, the tourist traffic picks up again, so I would not be completely on my own if I needed help. Still, it made me a bit nervous to torture test my truck on a highway hill in a wilderness mountain range 200 miles from home.


The trip out to Killer Hill made it clear that altitude does make a difference. As the truck travelled higher into the rarefied air, the cooling fan operation became longer and more frequent. When I arrived at the hill I made one preliminary run at lower speeds to get a sample data log with my laptop and determine if I needed to make any adjustments to my test strategy. This also allowed me to select turn-around points and to normalize the engine temperature. The long run back down the hill would serve to cool the engine and get it ready for each subsequent test run. All of the runs would start at an engine temperature of 185ºF. At 65 MPH, the intake air temperature for each run would begin at 52ºF. The hill starts at 5,800 feet and ends at 6,800 feet; just the conditions that I needed for my tests. The hill runs 3.7 miles long and there would be no problem getting the fan to engage, even at the cool ambient temperature of 47ºF.

Test Run #1: Stock LLY Air Intake

For the initial part of the first run, the engine temperature rise was not as sharp as my first experience on this hill. This was likely due to the much colder ambient temperature, about 47ºF compared to about 80ºF. I seemed to be climbing the hill with no significant issues. When the fan came on, however, things headed south rather quickly. Intake air temperature shot up to 103ºF – double the initial 52ºF. The engine temperature continued climbing until I could smell coolant at 241ºF. The engine had yet to reach its overheating specification of 250ºF but I was not going to chance it. I ended up backing off part of the way up the hill and continued slowly for the rest of the pull. At the top, I checked for the cause of the coolant smell – it appeared to be overflow from the surge tank, nothing to get alarmed about. Still, I was happy I had not taken the risk and pushed my truck harder. This test confirmed that the stock intake is a poor performer.

Test Run #2: Simulating an Aftermarket Cold-Air Intake

I removed the stock airbox and installed the LBZ airbox without installing the rest of the baffles specified in GM’s service bulletin. I also uncovered the holes in the fender to provide more air. I reprogrammed the ECM for the different MAF sensor scaling for the new airbox and moved the engine oil dipstick. Back at the bottom of the hill, I punched it again. This run did perform slightly better than the first. The intake air temperature was just slightly cooler than the previous run, the fan turn-on point was higher up the hill. But when the fan did engage, the same intake air temperature climb – thermal feedback – came into play. The ramp up was not as dramatic as it had been with the stock intake, but it was there. Intake air temperature reached 84ºF during the climb. Eventually, just within sight of the top of the hill, I was forced to back down. Engine temperature was back at 241ºF. This simulation of an aftermarket cold-air intake represented an improvement over the stock intake, but only a marginal one. For me, it reinforced the need to be very choosy about aftermarket cold-air intakes, if you should decide to go that route. Only those products that are true cold-air intakes – that completely seal off the filter from exposure to underhood warm air – would help relieve the thermal feedback that occurs in a stock LLY.

Test Run #3: Testing the GM Service Bulletin Solution

For the third test run, I installed all of the extra baffles and one duct specified in the GM service bulletin for the Chevy. It became quite obvious why those baffles are necessary – they completely seal off the air inlet from the rest of the engine bay and they manage the airflow so that the engine can draw sufficient external air. Turning around at the bottom of the hill, I began my third run. The fan came on at nearly the same point as the previous run, only this time the intake air temperature only reached 73ºF (compared to 84ºF on the second run and 103ºF on the first run). Yes, all the hot air coming off the intercooler and the radiator was still affecting the intake air, but the result was significantly better than in the previous runs. In fact, this run was the first time I could hold 65 MPH over the top of the hill. The engine temperature reached 237ºF. It was interesting to note the rate of the engine temperature rise. It rose quickly to about 235ºF, and then plateaued with the fan engagement, eventually peaking at 237ºF. This phenomenon indicated the effectiveness of breaking the heat feedback loop. With a lower intake air temperature during fan engagement for each consecutive run, the rest of the cooling system performed better and it did not seem to take much reduction of intake temperature to make the difference that we needed. Between the first and third runs, there was a peak intake air temperature difference of 40ºF. And between the second and third runs, there was only a difference of 11ºF. That change, however, made enough of an improvement to reduce the heat rejection of the intercooler significantly, allowing the radiator, in turn, to work better.

Any remnants of skepticism about the ability of the upgrades called for in GM service bulletin 06-06-04-036D to improve cooling system performance were now fully set aside. There is no question that GM’s solution works to reduce hot intake air feedback. However, if I had a hotter day, a heavier load and a slower climb, it may have been possible, still, to drive the engine into overheat; it would just take longer than it would with the stock air intake. The result was not as good as I had expected it to be. Still, with the typical towing conditions that I experience, the runaway overheat was essentially solved. Now there was one test run left. Would upgrading to the LBZ inlet duct make a difference? Or had the GM solution already brought the LLY to its peak cooling capacity?

Test Run #4: Installing the LBZ Turbocharger Inlet Duct

I felt good at the end of the third run. My truck was still in good shape: no coolant scattered over the ground and the GM service bulletin solution had made a measurable difference. I changed the turbocharger air inlet duct at the top of the hill in good spirits. I actually thought about heading home at this point – my fuel level was getting low – But I had committed myself to this test. I was not prepared for how impressive a change one part could make.

After turning around at the bottom, I accelerated back up to 65 MPH again. The truck felt quite different from the previous runs – it came up to speed too easily. After the second corner, starting up the long straightway, I knew, without even looking at the data pouring into my laptop, that the LBZ inlet duct was making a huge difference. My truck geared up much earlier, running fifth gear where I had been running fourth on the three previous runs. It felt like I had thrown 2,000 pounds of weight off the trailer. Also, the climb in engine temperature was definitely slower. In fact, the fan turn-on point was much higher up the hill than it had been for any of the previous runs. When the fan did come on, the engine temperature read 230ºF, where it stayed for the rest of the run. This was the first time that I had seen the fan keep the engine temperature under control, meaning that the temperature did not continue to climb for the rest of the run.

This test proved a very strong indicator that the LLY turbocharger inlet duct is unduly restrictive. The fact that the engine temperature was controlled on this last run – with the LBZ part – demonstrated that the intercooler was shedding less heat into the radiator. This tells us that the turbocharger was working more efficiently, creating less heat as it compressed the air to the desired boost level. But why did my truck appear to make more power?

To answer that question, I had to go back and look at the data logs recorded by my laptop. Remember that the turbocharger vane angle tells us how efficiently the turbocharger is working. Higher vane angle corresponds to more closed vanes, which requires more exhaust energy to drive the turbocharger. When this occurs there is more exhaust back pressure on the exhaust stroke of the cylinders. Less vane angle corresponds to more open vanes; less exhaust energy is required to drive the turbocharger. To see the significance of this, imagine the turbocharger as a variable supercharger, with the exhaust system being the equivalent of the drive belt on a supercharger. In the case of a belt-driven supercharger, the energy used to drive it comes from the crankshaft. Some of the combustion energy produced goes to drive the supercharger through the crankshaft and belt. A turbocharger has a similar parasitic effect, yet it is more efficient because it uses some of the waste heat energy in the exhaust system. However, the turbo still requires combustion energy from the exhaust stroke to generate boost, which ultimately steals some mechanical energy from the engine, much like the belt on the supercharger.

Consider the turbocharger vane angle as a rough measure of the exhaust energy being used to drive the turbocharger. Removing the restrictive LLY turbo inlet and replacing it with the free-flowing LBZ turbo inlet should make the turbocharger easier to drive, like removing a restriction from the supercharger. The data from the test runs supported this conclusion: the actual measured vane angle for all three prior runs to maintain peak boost levels was 68%. For the run with the LBZ turbocharger inlet duct, the vane angle was only 45% to maintain the same boost level. A 23% reduction to maintain peak boost is a huge difference in terms of the variable-vane turbo. That reduced the combustion energy (a result of reduced exhaust back pressure) required to drive the turbocharger by a large proportion. In all four runs, the load on the truck was generally the same: maintain 65 MPH with a constant mass and the same incline. The horsepower required from the crankshaft to drive the wheels is basically the same for all tests. However, the combustion energy underwent a measurable reduction with the fourth run, as less combustion energy was required to drive the turbocharger as measured by the vane angle. The data logs revealed another interesting detail that reinforced the fact that the truck was indeed making power more efficiently. For the length of the third run, made with the LLY turbocharger inlet duct, the truck spent 22% of the time in fifth gear. For the fourth run with the LBZ inlet duct, the truck spent an astounding 70% of the time in fifth gear. That, in itself, was an impressive change. It clearly demonstrated that a large parasitic load from the restrictive LLY turbocharger inlet duct had been removed. It also confirmed another suspicion that I had for a long time. There is a very short run of LLY engines in early 2006 that had all the LBZ parts on them. Their horsepower and torque ratings were the same as my truck, but they always seemed to feel stronger. Now I understood the primary reason why.

This change also has a dramatic impact on the cooling system. Less combustion energy equals less heat generated in the engine for the cooling system to accommodate. Consider that more efficient turbocharger operation reduces the heat workload of the intercooler as well, reducing the heat supplied to the airstream in which the radiator resides, improving radiator efficiency. All this results in a compound blessing: reduced airstream temperature that improves radiator performance as well as reduced engine heat load for the radiator. This creates another pleasant effect: reduced cooling fan operation, which became very apparent on the return trip home. On the way to the test hill, the fan engaged 23 times. On the trip back, it only engaged six times, and for shorter durations. A single part reduced the waste heat generated by the engine and turbocharger by a large margin, with a corresponding increase in power to the ground. Amazing, isn’t it?. When you look at the difference between the two parts (page 46) – it’s no wonder the turbocharger inlet duct was redesigned.

Which brings up another question: why doesn’t GM include this part with the service bulletin? The new, cold-air intake, by itself, does slow down the possibility of heat feedback, but the LBZ turbocharger inlet duct buys much more protection against overheating, not to mention increased power and efficiency. Add to that the increased longevity of the turbocharger itself due to a lower operating RPM: a win-win situation, no matter how you look at it. Surely GM engineering is aware of the benefits; after all, they redesigned the part. My recommendation for anyone who has had GM’s service bulletin applied to their truck: get the new LBZ turbocharger air inlet duct installed – even if you have to pay for it. It will pay you back in fuel savings alone, especially when towing.

One reason that GM would not include the LBZ turbocharger inlet duct in its service bulletin is that the 2004 Chevrolet Silverado with the LLY Duramax has a hood clearance that is much lower than the 2005 Chevrolet Silverado. The LBZ turbocharger inlet duct is somewhat taller than the LLY and so there may be a hood clearance issue with that specific truck. I spent considerable time trying to find a 2004 Chevy to investigate this, but they are few in number. Expect an update on this point. (This part will also fit the LLY-powered 2004-2005 GMCs and the 2005 Chevrolet Silverados.)

Unfortunately, the LBZ turbocharger inlet duct will only fit with the rest of the LBZ air intake system. It will not retrofit to the LLY. That means that the whole system will need to be upgraded to the LBZ specification. There is an alternative, however, if you choose to purchase an effective cold-air aftermarket intake, get an ‘06-’07 LBZ complete intake kit. That will bolt-up to the new LBZ turbocharger inlet duct, and will likely cost less than purchasing the entire GM system. A caution worth repeating: in order to stop the feedback loop, which is the other problem in this intake system, you need to purchase a system that completely isolates the underhood air from the intake.


maxxTORQUE in Print

(Available through Amazon.com)

Follow us on Twitter