LLY overheating - issues and resolutions

[Hunnington]

Just wondering if anyone has let GM replace the airbox as detailed in one of their TSB's to prevent 04 and 05 LLY from Overheating, and did it Work?

[killerbee]

The main issue I have found is a feedback loop between intake air, and the CAC heat.

Excess restriction in the induction tract exacerbates this feedback. A good CAI is vital.

[jbplock]

FYI ...

This TSB was updated recently ...

http://www.alldata.com/tsb/General-Motors/1158044400000_1159945200000_06-06-04-036C/60603601.html

[carco]

I see in the bulletin section a note about an 06 LBZ air box used to help reduce hot running temps on 04-05 LLY's, and a # of 1850306. Mine runs warm when towing. My dealer was unable to make the # 1850306 go anywhere. I searched the forums but found only one post alludeing to a GM bulletin about this. Any help would be appreciated. Thanks. bob.....

[WhiteTruck]

Doc ID 1850306 goes to TSB 06-06-04-036C just as it is supposed to. Have him try again.

[Kennedy]

Sounds like they tried to do a part# lookup rather than a bulletin search...

[carco]

Thanks for the help. bob.........

[Mark Rinker]

This sticky is to give 2004.5 - 2005 LLY equipped truck owners experiencing overheating issues a place to post their symptoms, questions, and to find resolutions.

If you have solved overheating problems with your LLY - please take time to post your experience here.

[Kennedy]

I run the OEM air box with mods shown on my site under Tech Tips (been there for a few years now) and a Uni foam air filter element. I run advanced injection timing and increased boost and have towed my 2002 out to MT and UT numerous times at 5 mph over most posted speed limit.

I definitely DO see oil psi reduction indicating to me that an engine oil cooler would be nice. I see increased ECT, but not so much as to be alarming and really only on the Continental Divide. Otherwise, the truck workes awesome. Yes the fan clutch runs and can be annoying, but it's there to do a job.

Do I think there is a benefit to doing the 06 air box? I'll say it surely cannot hurt and is a step in the right direction. Be sure to have the programming updated as well to match the air flow/MAF placement characteristics of the new box.


Additionally, I think the 2006 style transmission cooler is a good idea and better yet the larger version from Inglewood Transmission. This is the way that I prefer to set up the trans cooler.


As a last ditch effort to cool a hot running LLY you can try the "pony" radiator found at www.coolmyduramax.com I'm not necessarily trying to endorse these mods as I have no first hand experiece with them, just pointing out their availability and potential to help. I've spoken with others who have had good results with them.

[Mark Rinker]

Personally, I am intrigued by the idea of additional oil cooling, combined with an improved intake that eliminates induction of underhood air. Both of these approaches address the LLY heat soak problem at its roots, rather than at its ends.

I may add additional oil cooling to all my rigs as a good measure of protection.

[rickdlance]

Personally, I am sold on the idea of additional oil cooling, combined with an improved intake that eliminates induction of underhood air. Both of these approaches address the LLY heat soak problem at its roots, rather than at its ends.

I may add additional oil cooling to all my rigs as a good measure of protection.

You do realize that the first place the coolant hits as a "cooling" device is the oil cooler. By reducing water temp you effectively add oil cooler capacity automatically. Then the "cooler" coolant goes on into the engine and continues to be effective in places the oil never see's. All this without disturbing GM's critical oil flow design. What ever you guys decide to go with, Good Luck.;)

[Mark Rinker]

"...by reducing water temp you effectively add oil cooler capacity ..." Are you suggesting that under normal operating conditions the oil temperature at the oil/water cooler is lower than the water temp?

Are any of your DMax's LLYs? Any overheating issues? How are they used - i.e. towing, hauling, ???

[rickdlance]

"...by reducing water temp you effectively add oil cooler capacity ..." Are you suggesting that under normal operating conditions the oil temperature at the oil/water cooler is lower than the water temp?

Are any of your DMax's LLYs? Any overheating issues? How are they used - i.e. towing, hauling, ???
Wow, somebody that doesn't know how hard we are on trucks.

All 4 of my current trucks are LLY's, even my 03.:)

I am the definition of hard on them, and yes I have had overheating issue's. I've put my truck's out there repeatedly to test "cures" for a couple of years now. Spent two days in the Kennedy Torture Chamber.:)

Only one thing I've found so far that gets them under control and its out of Texas, but I'll continue to test products as provided.;)

[More Power]

The new '08 Ford 6.4L F-250/350 series pickups are using a radiator that was originally designed for their medium-duty pickups - something like 50% more capacity than their 07 models, and the water pump was uprated to 130-gpm. The CAC (charge air cooler) was also upsized. From what I've read, the much larger EGR cooler (required for the 07 emissions) is mostly to blame for the increased heat rejection requirements. I also suspect keeping coolant temps as close to the thermostat rating to help control NOx emissions is also a factor.

The LB7 for the most part didn't have a temperature problem. What's the difference between the LB7 & LLY that could affect engine temp? Turbos, EGR coolers, programming....
Jim

[More Power]

On a related note... We ran RJ's 6.5TD Suburban at last summer's Pull-Off. This was the first time I witnessed a 6.5 that could run full-pedal at 3000+ rpm for the full mile (6% grade & 10k trailer), and not experience excessive EGT and/or ECT.

The turbocharger was the biggest part of the reason why. The factory GM turbo is too small to allow the engine to operate at high RPM "and" at full power. Correctly sizing an aftermarket turbo for the performance goal allowed the engine to produce a lot more power without temp problems.

Then and now, I couldn't help but wonder if the Garrett VNT is part of the problem with the LLY - and for the same reason.

With the 6.5TD and stock turbo, owners need to pull at a lower rpm. Boost is higher and the engine produces its best towing performance at a lower rpm. A more or less stock LB7 produces a "pulling" EGT max of 1250 when at about 2400 rpm. Allow the LB7 to run up to 3000+ rpm at full-pedal with a heavy load, and it too will produce 1400 degrees or more. Turbo sizing, pressure ratio, and turbo efficiency are among the elements that determine where to run the engine for best and most efficient power.

If there was a way to install one of the performance LB7 turbos offered by Garrett, BD, ATS and others on an LLY, I'd bet the overtemp issues would disappear. ;)

Jim

[Ranch55]

The coolant in any system serves only one purpose. That is to remove/transfer heat.
The oil/lubricating fluid serves two purposes. Lubrication and remove heat. This is the basic properties we look at when sizing coolant and lubrication systems for the big major machinery applications,,,,,,i.e...refinery gas turbines, reciprocating compressors, and other general purpose rotating machinery.
Sometimes we have to add additional cooling on the oil side because the coolant side is inadequate or not enough available. Lowering coolant temperatures does not equate to automatic additional oil cooler capacity. The coolant flow rate, temperature, and capacity in the cooler dictates heat transfer properties. Too fast a flow rate, and there is minimum heat transfer. Too slow a flow rate, and there is coolant overheating, which prevents enough heat from being removed from the oil.
I opted to add additional cooling on my '05 LLY via lowering the temperatures on the oil (engine & transmission).
I installed the '06 Inglewood Transmission cooler. This was quite an improvement. It lowered the overall operating temperature of the transmission by 20~30 degrees F, depending on load and ambient temps. The heat being transferred from the transmission to the engine coolant was reduced.
I then installed an engine oil cooler with a regulated Mocal 180 degree thermostat to maintain proper engine temps. and not run too cool.
With the additional oil/trans. fluid cooling, my temps never run hot any more (according to OEM gauges, this is the only reference I use). I'll pull any rated load and not worry at all.
Anyway, this is some of my thoughts and experiences. I enjoy reading the all the ideas and viewpoints.
One Team,,,,One Goal !!!

[Mark Rinker]

Any Duramax that tows heavy and regularly in hot temps could benefit from these mods. Can you post the part numbers for these coolers? Any installation comments or pictures to post?

[Ranch55]

Any Duramax that tows heavy and regularly in hot temps could benefit from these mods. Can you post the part numbers for these coolers? Any installation comments or pictures to post?

Click on my ID and go to my homepage. I have several photos showing the transmission cooler and the engine oil cooler.
Don't have part numbers, these are not GM OEM parts.
The transmission cooler is Mike L's at Inglewood Transmission. It does use 2006 GM OEM fluid lines.
The engine oil cooler is the TD-EOC discussed on other forums. I have found it to be very reliable and efficient.

[killerbee]

Personally, I am intrigued by the idea of additional oil cooling, combined with an improved intake that eliminates induction of underhood air. Both of these approaches address the LLY heat soak problem at its roots, rather than at its ends.

I may add additional oil cooling to all my rigs as a good measure of protection.


I am still trying to create that better air intake, one that doesn't allow IAT to skyrocket when the fan engages.

This has been tougher than it sounds.

[REDTRUCK05]

This sticky is to give 2004.5 - 2005 LLY equipped truck owners experiencing overheating issues a place to post their symptoms, questions, and to find resolutions.

If you have solved overheating problems with your LLY - please take time to post your experience here.
I bought my 05 LLY new. 2500HD crew. WHENEVER I pulled, the fan would run at any speed below 60 about 80% of the time. Noisey and big drag on engine. Ive heard GM has put out a kit that changes the fan pitch to be more productive, thus running less. I sold mine, got 07 gmc lbz. love it so far

[killerbee]

I bought my 05 LLY new. 2500HD crew. WHENEVER I pulled, the fan would run at any speed below 60 about 80% of the time. Noisey and big drag on engine. Ive heard GM has put out a kit that changes the fan pitch to be more productive, thus running less. I sold mine, got 07 gmc lbz. love it so far

The 06 and newer truck have a new fan, but it is just as noisy and very parasitic also. It is also about 40 or 50% larger in area.

The worst part about the fan and its integration, is that it creates an IAT rise. This IAT rise causes much more heat to be discharged by the turbo into the intercooler, where the added heat rejection keeps the fan on. It is a nasty feedback loop for warmer weather use, or heavy hill towing. Altitude makes it worse also.

[Kennedy]

I've made a lot of dyno runs some with the fan clutch engaged and yes there is a power reduction, but it is not as monumental as one would think.

[More Power]

I've made a lot of dyno runs some with the fan clutch engaged and yes there is a power reduction, but it is not as monumental as one would think.

As veteran 6.5TD owners will attest, overheating is a much worse problem than losing a few HP and hearing more noise when the fan-clutch engages. If you have to pull over during a long climb up a steep grade, you lose all the horsepower your engine is capable of.... :(

Jim

[killerbee]

My opinion on why power reduces to nothing at the end... Timing tables.

Timing is obviously an important parameter for torque stroke power production. It is important that the heat unleashed after TDC be more than what occurs before TDC. When ignition occurs to early, then there will be counterproductive (negative) torque applied to the crank. The basics.

diesel typically ignites at a given temperature and pressure in the cylinder, compression dictates this rising temperature as the cylinder approaches TDC. With our compression ratios, intake air at 100 degrees will be 1300F when fully compressed to TDC. If intake air is 200 F, that 1300 F comes 10 degrees sooner, about 10 BTDC. Hypothetically, if our diesel mix autoignites at 1300, then the effect of increased intake temp, is to create counterproductive torque, and 10 degrees of counterproductive torque. This is a little simplified, but very applicable. The warmer charge also reduces ignition delay, effectively advancing timing. From there, combustion occurs quicker. The hotter cylinder zone temps create the same problem.

So, if our truck is running injection timing at 15 BTDC, a hot intake charge will mean certain power loss as IAT is increased. The way to counter this is to retard timing with this increasingly warmer intake temps.

I'm no expert, but I think the 6.5, with no CAC, would be very prone to this, since intake air is not moderated with cooling. Any increase in airbox temps, translates to increased intake temps, with a factor of 140%. A 100 degree rise in airbox temps, yields about a 140 degree rise in intake temps. Power loss results from the early ignition, and some PCM's thankfully defuel at this stage. (If it didn't, increased cylinder pressures could blow up the motor.)

with the LLY, there is no timing adjustment for increased IAT, or overheating ECT for that matter. But that's not hard to change ;). I can't speak to the 6.5 PCM.

[Kennedy]

I won;'t get into a debate with someone who knows so little about these engines/trucks. Suffice to say, I add quite a bit of timing to ALL of my tunes and they pull very well in any climate.

My 50HP economy/tow tune for the LLY (40HP with no pulse increase) does not really add much fuel and is what Rick Lance uses to tow unless he hits super headwinds and needs to switch it up a notch...

[killerbee]

I guess high EGT's are good for keeping things from overheating. ...

yes, that is correct. EGT and ECT rise are somewhat inversely correlated with timing change. With timing advanced, the coolant is exposed to a longer duration of peak cylinder temperature. So more heat is transferred to it.

This thread is about overheating issues. If you would like to prove me wrong, go for it. But EGT is not the place to begin a discussion on how a motor digests or disposes of heat.

EGT is a measurement of your exhaust temperature, downstream of the motor. It has nothing to do with heat transfer in the motor itself.

You can experience high egt, yet the cylinder temperature itself can remain unchanged, at well over 4000 degrees peak.

I am talking about retarding timing dynamically, as conditions require the change to re-optimize timing for an always changing combustion environent.

[More Power]

I feel EGT is directly related to ECT. If it wasn't for the exhaust runners in the cyl heads, it might not be - quite as much. But, a lot of heat is dumped into the cooling system as a result of the exhaust flame snaking through the exhaust runners in the cyl heads.

There has been all manner of experimentation through the years in all manner of engines that attempted to isolate the heat from the exhaust runners. The best approach I've seen of late has been ceramic coating of the exhaust runners.

Jim

[killerbee]

EGT is usually measured external to any cooled surface, after exhaust has left the building. How can it possibly be relevant to cooling loads in an overheating discussion? It is not a measure of the temperature of a water cooled surface.

High EGT is more a measure of how much combustion (expansion) did not take place in the cylinder.

Quoting a physicist, C Johnson, from Chicago:



[INDENT]This discussion is going to be about the so-called spark-ignition or Otto cycle engine, the process that virtually all cars and trucks operate on, and applies to the diesel motor as well. There are a couple common alternatives: The compression-ignition or Diesel cycle and the Brayton or Joule cycle. The majority of this discussion actually applies to all three, but there are some differences. In Physics-talk, an Otto cycle has an isentropic compression, followed by a constant volume combustion explosion, followed by an isentropic expansion. In contrast, a Diesel cycle has an isentropic compression followed by a NON-explosive combustion at (relatively) constant pressure, followed by the isentropic expansion. Enough of that! They're much alike in many ways, and you can consult any College Engineering textbook regarding the differences...


When the piston began its upward movement (at BDC, bottom dead center), there was then a volume of gas-air mixture above it of (44 + 6.3) or 50.3 cubic inches. When the piston has gotten to TDC, all that gas-air mixture has now been compressed into the remaining 6.3 cubic inches. The ratio of these numbers, 50.3 / 6.3 is called the Compression Ratio of the engine. In this case, it is about 8.0. ...

Most superficial descriptions of automotive engines then say that the gas-air mixture is ignited at that moment and that the even higher pressure of the exploding gas drives the piston down, turning the crankshaft. Reference is usually even made of 'advancing the timing' of the ignition spark, so it occurs maybe 10

[killerbee]

The best way I know of to reduce EGT are:

1. reducing exhaust restrictions
2. reducing intake charge temperature.

You can get over 300 F reduction with these 2 suggestions, there may be others. I have tested number 1, and the effects on ECT. It reduced EGT 150-200 degrees, and provided no help to overheat resistance. Number 2 did provide overheat resistance. There is a clear cut reason for that, though at the time I wasn't aware of what it was. It was because lowered IAT allowed the CAC to stay cooler, which lowered intake charge temps, yes, but kept the CAC from being such a heat source to the radiator.

So, IMO from these 2 experiments, and comparing the results, I do not believe EGT play much, if any, role in overheat resistance with high loads.

again, egt is not cylinder temperature, it is far removed from it. IMO, egt poses no threat to anything accept the turbine, and that is all. Off topic: I do not even subscribe to using it for timing shutdown. I used to, but not since I saw egt under 400 while oil was still over 300.

if peak cylinder temperature was known, I would use that as a predictor of ECT, all other things held constant, if that clears anything up.

[More Power]

The EGT pyro in my Duramax is an inch or two from the #8 exhaust port. I doubt the exhaust gas temperature there is a whole lot different than it is inside the exhaust port - in the cyl head - which is cooled by coolant. ;)

My point is not about timing, but about the heat load the cooling system has to deal with. Whether advanced, retarded or spot-on, the heat in the exhaust runner is still affecting ECT - whether good, bad or indifferent.

Jim

[killerbee]

The EGT pyro in my Duramax is an inch or two from the #8 exhaust port. I doubt the exhaust gas temperature there is a whole lot different than it is inside the exhaust port - in the cyl head - which is cooled by coolant. ;)



sure...no argument. In fact it is warmer in the port. but just so I am not being misunderstood,

exhaust reduces in temperature, not because it is cooled (much), but because it is constantly expanding. Just like compressing a gas charge heats it up, letting it expand more efficiently allows it to reduce temperature. An adiabatic concept. Obviously we dont have 1200 degree gas out the tailpipe, it is a fraction of this. This explains the importance of exhaust restriction removal on EGT, and why removing the cat and muffler reduce EGT's.

It is the backpressure at the number 8 location that is primarily predicting your EGT, all other things constant. Removing all that downstream resistance allows that pressure to reduce very rapidly, and mere inches are the difference measured in 10's or 100's of degrees. These gases began life at 3000-4000 degrees. Only expansion (hence torque) brought them down to 1200.

Expansion also explains the 200 degree disparity between pre- and post-turbo readings. The turbo is not "cooling" the gas (much), there is not enough conduction time in that environment. The gas is expanding through the turbine.

It's no different than the freon freesing your hand. It's room temp inside the bottle. Expanding it adiabatically, sends the temp down.

[dieseldummy]

Yet again KB shows just how much he knows about diesel engines... Take any diesel engine. It can be in a pickup, big rig, or tractor. Run the motor at full load for any period of time at 1000 degree EGT's. Usually the coolant will stay within acceptable range. Bump EGT's up to 1200, usually you can notice a 10-20 degree change in ECT because that hot air is heating up the entire motor... not just the exhaust. If you run up into the 1400 degree range things will usually get out of hand rather rapidly in the ECT department.

Take the motor that will run at 1000 degrees all day and pull some timing. Back it off only 2 degrees and see what happens. Suddenly the EGT's are that of the 1400 degree motor... ECT climbes rapidly as a result. Inversly take that 1400 degree motor and bump the timing on it 2 degrees. It will probably turn into a cool running machine that can be worked for hours with no ill effects. If you don't believe me go run some diesel machinery for your self and find out.

Like MP points out there are exhaust runners in the head that heat the coolant up. The exhaust manifolds are bolted to the head its self which helps heat every thing up. The combustion chamber is surronded by coolant, so if the heat doesn't go to the coolant then where does it go? Just thank god you don't have precups in the head to help out...

There are usually 4 main contributing factors to keeping EGT's under control: Fuel rate, timing, exhaust restriction (be it the tail pipe or turbo housing), and charge air temp. Take this how you will, but with stock everything retarding the timing is the last thing a person wants to do. 4" exhaust neted me 125ish degrees in EGT reduction. That's good, but there's alot more to be had. Nobody has proven that aftermarket I/C's are worth the money, so that aspect is kind of an unknown. The stock intake has proven to flow well, and filter great so it stays. That leaves timing and fuel rate...

Let me start by saying that in stock form my '01 will reach 1350+ on they pyrometer when towing. (before exhaust) I made up a simple tune with EFILive that adds approximately 15% more fuel and uses modified (advanced) timing. I also added alot more fuel in the low RPM ranges so I can leave it in 6th gear and make it up hills. With this tune I only ran 1325-1350 EGT's. (before exhaust) Lower EGT's with more power??? Surely not... Well, it's true. After the exhaust I now run 1250 and have enough power to lug up the hills at 65 mph (speedlimit).

Tell me KB, what really makes a difference in the EGT department. Tuning or exhaust/intake???

Respect? What's that? I have respect for real vendors who solve problems instead of talking about them on internet forums. When the 6.5's broke blocks JK had some splayed main caps made and DSG made a main girdle kit. Both helped to solve a problem. When all of our pickups started making enough power to tear up transmissions ATS and Suncoast steped up to the plate and came up with a solution. Southbend made clutches for us ZF6 guys. As far as I can tell when LLY's started overheating you and that TXChris got in a pissing match on the forums. The only difference between you is that adding a secondary radiator seems to be the closest thing to a fix yet... To your credit I've never seen a dumbass video on youtube about an overheating Dmax from you.

[Kennedy]

The best way I know of to reduce EGT are:

1. reducing exhaust restrictions
2. reducing intake charge temperature.

You can get over 300 F reduction with these 2 suggestions, there may be others. I have tested number 1, and the effects on ECT. It reduced EGT 150-200 degrees, and provided no help to overheat resistance. Number 2 did provide overheat resistance. There is a clear cut reason for that, though at the time I wasn't aware of what it was. It was because lowered IAT allowed the CAC to stay cooler, which lowered intake charge temps, yes, but kept the CAC from being such a heat source to the radiator.

So, IMO from these 2 experiments, and comparing the results, I do not believe EGT play much, if any, role in overheat resistance with high loads.

again, egt is not cylinder temperature, it is far removed from it. IMO, egt poses no threat to anything accept the turbine, and that is all. Off topic: I do not even subscribe to using it for timing shutdown. I used to, but not since I saw egt under 400 while oil was still over 300.

if peak cylinder temperature was known, I would use that as a predictor of ECT, all other things held constant, if that clears anything up.


1) I'd love to claim big EGT drops to sell my exhaust. About 60 degrees EGT with an exhaust system in a controlled environment with fast acting OPEN TIP thermocouple. 100 degrees peak maybe.

http://www.kennedydiesel.com/photogal/images/KD-4-5-Exhaust-EGT-and-Boos.gif

2) I've towed in the mountains across the divide etc. Starting out IAT can be high, but once underway, they seem plenty acceptable to me hanging within a few degrees of ambient most of the time using a Uni foam filter in a modified stock box.

http://www.kennedydiesel.com/dmaxairintake.html


As for EGT not impacting ECT I guess I guess I forgot that Dmax used a special heat rejective aluminum alloy in their heads to keep the heat of the exhaust out of the heads and cooling system. ;)

On Oil temp, cooling it is a great idea. It was a good idea when Rick Lance brought his cooler (designed from the ground up :rolleyes: ) and adapter to be tested.

[killerbee]

Run the motor at full load for any period of time at 1000 degree EGT's. Usually the coolant will stay within acceptable range. Bump EGT's up to 1200, usually you can notice a 10-20 degree change in ECT because that hot air is heating up the entire motor... not just the exhaust. If you run up into the 1400 degree range things will usually get out of hand rather rapidly in the ECT department.



I don't agree with anything you have stated. The context was changing timing, and it's effects on EGT. ( Not how overfueling affects EGT, and thus ECT.) You changed the context by introducing changed tuning parameters aside from timing.

I stand by my statement: all other things remaining the same, just advancing or retarding timing does not affect ECT, though it does affect EGT. And that over advanced timing (a result of increased IAT and cylinder heat soak) is a significant source of non-optimum timing that contributes to overheating.

[dieseldummy]

Well, if timing doesn't affect ECT then how does too much advance cause overheating??? I really feel bad for the uninformed diesel driver that falls for your BS... Almost as bad as Banks advertising hype.

[killerbee]

Well, if timing doesn't affect ECT then how does too much advance cause overheating??? I really feel bad for the uninformed diesel driver that falls for your BS... Almost as bad as Banks advertising hype.

accept...I'm not selling anything.

go figure it out for yourself. I'm done talking to such a rude person.

[dieseldummy]

TD-EOC ring a bell?? how about fruitcake vendor on another site... Not selling anything my ass.

I've got it figured out thank you very much. Once again I suggest you do some research on the operation of diesel engines and rethink your position about this. I'm only rude to people who talk at me and not with me KB...

[killerbee]

This became a project for me about 3 years ago when the LLY was released. It was a slow learning process. I had to dissect every mechanism in the vehicle to finally track it down. For me the heat transfer mechanisms were easy to log, easy to track and easy to assemble. The thermodynamic mechanisms, and what would turn out to be hidden flaws, were much more difficult to nail down. I had to dust off compression thermodynamics to finally arrive with my finger on the cause.

So I’ll start with the statement, then I can explain the rationale. For the most part, the changes that brought about LLY overheat, for those that utilize the vehicle in severe work conditions, are 1) the elimination of the wastegate, through adoption of the variable geometry turbocharger, and 2) the reduction in size of the induction plumbing…CAC boost tubes. It is also important to note 3) the fan coupled IAT rise. This is not a change for the LLY, but it is a critical element that magnifies the effect of 1) and 2).

1. Wastegate. By and large, the wastegate has multiple functions. For this discussion, the applicable feature of the wastegate is its inherent ability to put a hard ceiling on the work performed by the compressor. Most people just recognize that it limits boost, bypassing exhaust flow when the preset compressor boost limit is reached. That boost is sensed at the compressor discharge where the wastegate line is located. But also, in a real thermodynamic sense, it limits the heat that the compressor can generate. I will skip compression thermodynamics; accept to state that the turbo creates a lot of heat in the charge air (measured up to 590 F). As IAT goes up, then this heat also goes up, increasing by 150% of the IAT change. This creates higher tube velocities and friction losses. The real magic of the wastegate is that as IAT gets hotter, the compressor is moderated to keep from further heating the charge air. Physically, you would see a decrease in intake plenum pressure as IAT increases, while discharge pressure remains pretty much constant. The reason this is, is that the wastegate controller maintains a hard boost limit on the discharge, and this equates to a quasi-hard limit on heat production.

The VGT cannot do this!

It has no boost or heat limit protection, no wastegate, nor even a PCM code to detect this issue. When IAT heats up and begins to heat charge, there is NO MECHANISM to limit work (and heat) produced by the compressor. Where the LB7 boost is controlled to a discharge limit, the LLY is controlled to the intake plenum requirements of the MAP sensor. It asks for 20 psi, and if there is 400 mph air charge due to heating and a 7 psi loss in the plumbing, then the discharge is commanded to 27 psi. It’s that simple. With this much discharge boost, the compressor is operating off the map much of the time, especially at higher elevations. This means yet more heat due to the lower operating efficiency of higher boost.

2. Plumbing sizing. This is a critical science by itself, all fluid transport systems must have carefully calculated ductwork to minimize plumbing losses. When dealing with adiabatic compression, it is ultra important. Restriction means lost boost and added heat. GM botched this step. The LLY emerged with very restrictive boost tubes, undersized for the application; from the LB7’s 3” to 2.5”. That increased charge velocity in the pipes 44%, leading to significantly larger losses, between 2 and 3 psi of additional restriction. An awful waste of boost, and tragically, huge consequences in heat production. So the heat machine (VGT), sends the resultant heat product to the CAC, where with all its added heat load, rejects tons more heat into the ambient stream, firebombing the radiator in effect, with ambient as hot as 240 degrees.

So the radiator has plenty of capacity, when it receives the intended cool air. The problem is what happens with the LLY in front of the radiator… no cool air to do the job of dropping coolant temp.

With EFILive, it is possible to create a software “wastegate”. I have been playing with this concept for a few months. It requires careful slight boost reduction with increasing IAT and elevation

Anyone can resolve the overheat issue by employing a cold air intake, with larger boost tubes. I have had very good results with this, I’ll see if I can find the charted data.

You can mask it with cooling system expansion, but you are still left with all the byproducts of poor induction design. The main one is that intake temp (post CAC) can get real high, over 250 degrees, and this leads to significant oxygen loss and power loss on the grade. The ONLY way to address that is keeping IAT down with the correct CAI, and then helping out the efficiency issue further by using the larger boost tubes so that the compressor does not have to work so hard. It’s the simple frozen milkshake and straw experiment. Use a bigger straw and you will give your cheeks a rest, basically create the least restriction possible in the plumbing.

Because it has to work less, the turbo rpm is reduced by 10,000 rpm, and this means lower exhaust backpressure, (more HP to the wheels) and 100-200 degree lower EGT’s, not to mention a grateful turbocharger that will outlast your neighbors as you are passing him on the grade. ;-) When power is up, grade speed is up, which is good for cooling. These are the kinds of improvements that are a win-win-win. Even your tank of diesel will go further. The best part about this is its all passive, my favorite kind. It works full time without batteries, relays, fans, water, or unreliable moving parts.

Flame away.

Michael Patton-Enervative Product Engineering