'07 LBZ Air Intake Roar

[BradL07]

Greetings to All:

I am a new owner of an '07 Chevy Classic 2500HD with LBZ, having graduated from an '01 Chevy 2500HD with LB7.

Comparing the LBZ to the LB7, I am noticing a lot more turbo whine with the LBZ, which I attribute to the improved air box on the LBZ.

But I'm also noticing, sporadically, on a "cold" start, an intermittent "roar" under the hood with the LBZ - like the air intake is choked off and the engine is trying to suck a large amount of air thru a small opening.

I've checked thoroughly for any foreign objects, etc. and only noticed the baffle at the passenger fenderwell, near the bumper, was loose in the fenderwell, and that's since been secured by the dealer in its proper location via caulking.

But sometimes I still get this "roar" when taking off, after the truck has set overnite or at the parking lot during the day. Normally, all I ever hear is the turbo whine. Otherwise, the LBZ is so much quieter than the LB7.

Anybody have any idea what this periodic "roar" may be attributed to? Anything to worry about?

BradL07

[Duramaster]

One major difference from your old DMAX is the cooling fan. I had to change a belt on a 2007 Sierra classic yesterday, What a pain!!! The improved cooling system moves alot more air!!!:)

[BradL07]

Good point Duramaster. I had the same thought but discounted it since the "roar" seemd to occur at "cold" start, if you can have such a thing in Houston.

I assume the cooling fan has to be thermostat activated? So perhaps I may have an electrical glitch there.

BradL07

[JohnC]

It's a thermostatically activated fluid clutch. When the truck sits the fluid puddles up and locks the clutch. After a minute or two of running at road speeds the fluid redistributes itself and it unlocks.

[BradL07]

Aha....thank you John C, I believe that explains my situation exactly. As you describe, after driving a few miles, the "roar" would be gone. Hard to believe the cooling fan can be that loud at lower speeds, but it definitely is!

[DieselMonk]

have the same thing with mine. I wish there would be a fix for that.

[DmaxMaverick]

have the same thing with mine. I wish there would be a fix for that.

There is a "fix" for it. Remove the acc. belt. Caution--There will be side effects.

This is nothing new. All fan clutches do it to some degree. "Heavy duty" clutches are more aggressive, so will engage more aggressively, which is compounded by a more aggressive fan. The alternative is poor cooling system performance. GM doesn't want to go there again, and neither do we.

You have two choices. Noisy fan, or overheating while trying to crest a grade in the summer. I've had both, and I'll take the noise every time.

[tooltime47]

I've had my truck for three weeks today. I got the same roar that you are describing for the first time today. I drove another one before I bought this one and it did it also. I would think if is an issue with the fluid in the clutch, it would do it all the time. We have had colder days than today I don't think it is temperature related.

[BradL07]

Agreed on the temperature not being an issue - like JohnC says it seems related to "fluid puddling" in the clutch.

[EdHale]

My 2006 LBZ does it too, but only for about 1/2 mile and only once or twice a week, not every morning. Ed

[Dakster]

You guys got me thinking yesterday so I paid attention. Every morning I start up my work car and then finish loading up for the day. It's a Ford Taurus and quite loud from the engine compartment area at 6am. This could also be why my wife's 2004 Volvo sounded so loud when I first starting it. Both cars after a minute or so would quite down considerably.

I haven't tested her new VW TDI yet.

I didn't notice anything with the 2007 LMM's I drove, but I could barely hear the motor at all. My wife actually asked if I was sure I was driving a diesel. Apparently, GM didn't lie when they said they added extra sound proofing in the new trucks.

[cmwilga]

I live in Texas and have a 2002 that roars sometimes for about 1 1/2 miles after starting up then quits. I have also noticed it doing it in 102 degree weather while pulling a trailer. Same sound. Fan clutch no doubt.:eek:

[fajitatone]

I got mine in november 2006 and it has done it periodically. Hell, it happened this morning. I live in Miami, where it's 80 degrees by 10 AM and I figured it was the fan. Now I know it's puddling clutch fluid. I would rather hear the sound and know the engine's cool, than see a dash full of Check Engine lights.

:rolleyes:

[killerbee]

.

Comparing the LBZ to the LB7, I am noticing a lot more turbo whine with the LBZ, which I attribute to the improved air box on the LBZ.



The variable vane turbo in the new truck sounds more like a small jet than the older style wastegated IHI.

[Destroyer]

I had this happen to me I pulled over one morning and checked it out. I opened the Hood and a 750 lbs Tiger jumped out and took down a neighbor kid on the way to school. I guess it crawled up there to get warm. What a way to start your day.

Seriously, I had this issue with my 454 Sub when it was hot. I am glad I saw it here as I plan to move to Alaska and I will have this most days now I won,t freak out and take the Casull to it. http://www.fishandhunttexas.com/454casull.htm

I did the Banks Monster Exhaust, Banks Intake and Super chip programmer. I noticed the Beast is very quite now.

[Destroyer]

I think this explains it all very well.
http://www.innerauto.com/Automotive_Systems/Cooling_System/Fan_Clutch/


I guess if things a out of whack then what is happening is the fan is spinning up at full speed. It reduces HP and Torque which is why sometimes it feels as if the car in running over Moleasses. In a sense you car ,truck or what have you is trying to be an Airplane with out wings due to the fan trying to do 3000 rpms as opposed to spinning just fast enough to do its job. I wonder who thinks this stuff up they must be just as strange as me. I saw a truck once it had 350 Chevy it had three electric fans and an electric water pump. I was shocked to see no fan mounted on the engine.

Hope you all enjoyed the link.

[BradL07]

Now that I understand what is happening, I'm not as worried. But still, hate to hear that "roar" a couple times a week after a "cold" start.

[Axle]

My new 2007 Silverado Classic also has this intermittent fan roar. It only seems to happen when the truck has not been run for a day or two. Then it happens upon first start.

The roar is amazingly loud even at low speeds. Would anyone here consider this a warranty issue? Or would the replacement fan clutch do the same thing?

Seems like the consensus here so far is that nothing is really wrong but that the design has a short-term, annoying loud noise.

[Dakster]

Axle,

As I agree in the annoying department, I don't think there is anything the manufacturer can do unless we want overheating problems like in the past. To me, at least I know the fan/clutch is working and I try to take it easy the first 1 - 1 1/2 anyways.

I live in Miami as well, I bet by noon it is 150+ degrees under the hood and I bet that coil spring has let a lot of fluid in and not out. I couldn't tell you exactly how hot it gets because the thermometer maxes out at around 145 and it is pegged. Once you get going the movement of air cools the clutch and the fan stops spinning.

Annoying and should it happen, probably not. But I'd rather have the noise and not worry about overheating.

[40grit]

mine does it too, I took it in for service a while ago, they said GM's stance is as long as it shuts off at normal op temp and turns on if it gets hotter, it's working OK, GM has no need or desire to replace it due to fluid settling during sitting. mine does it randomly now, sometimes in the morning, other times after sitting a few hours during the middle of the day, no rhyme or reason. sounds like a cessna taxiing for a takeoff when it turns on...

[JohnC]

Years ago a friend of mine asked me to look at her ford pu. Problem was lack of AC and hot running in town, fine on the highway. The fan clutch was shot. When I replaced it she complained of roaring on startup.

Get over it!

;)

[killerbee]

mine does it too, I took it in for service a while ago, they said GM's stance is as long as it shuts off at normal op temp and turns on if it gets hotter, it's working OK, GM has no need or desire to replace it due to fluid settling during sitting. mine does it randomly now, sometimes in the morning, other times after sitting a few hours during the middle of the day, no rhyme or reason. sounds like a cessna taxiing for a takeoff when it turns on...

The viscous slip medium in the clutch is a form of silicone, it's flow from chamber to chamber is modulated by a temp sensitive spring.

If the vehicle has some heat buildup under hood when it is shut down, The spring heats up and permits fluid movement while it is sleeping.

The term usually associated with your annoyance (and mine) is morning sickness. After I added a few changes to the front end, I rarely ever have that happen any more.