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Old 04-06-2010, 09:45 AM   #1
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Ah, Houston, we may have a problem.

After doing, what I thought was thorough research, I purchased a late 2004 LLY 2500. Since then I have pulled our 11,000 - 12,000 fifth wheel only a couple of times and through mostly flat terrain. Last weekend was it's first true test. The wife and I drove from Phoenix up to Payson, AZ. A drive that is fairly hilling and an overall elevation climb of 3,000 feet. During one of the inclines I noticed the temperature gauge had jumped from the nominal range of 210 to half-way to the red zone. Just as I noticed this, I heard this tremendous sound - like it had a second turbo charger or something. I then watched the temp gauge drop back down to 210 in about 15 seconds - while still climbing the hill! The rest of the way up to Payson, I could hear, what I assumed was a secondary fan that I was not aware of, kick on and off - usually for no more than 10 - 15 seconds and the temp stayed in the normal range for the rest of the trip up and back. When I got home, I started googling to find out what the sound was and discovered it was the fan clutch locking up and running at nearly engine speed. OK, I thought. While I was a little un-nerved that the temperature had gotten that hot to begin with I was also relieved that Chevy had engineered a way to rein it in. However - in doing my research on the fan I found a boat load of user comments about the overheating problems with the LLY! Dang it - I thought I had done a good job of researching our truck purchase. I'm not ready to accept that I have a problem - yet. Other than that short period of hot running, I thought the truck performed very well. I especially appreciated the auto grade braking.

Are there other LLY owners out there who are NOT experiencing significant overheating issues? Are there any reasonably priced after-market fixes?

Truck info: 2004 2500 Duramax/Allison LLY, extended cab, long bed, completely stock, I'm the second owner and first owner never towed with the truck. I've owned the truck for about 9 months, put about 5,000 miles on it and this is the first time I had heard the fan clutch lock-up or had seen the temp gauge go over 210. Truck now has approx. 80K miles on odometer.

Thanks in advance.
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Old 04-06-2010, 11:45 AM   #2
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After doing a little more research, it appears this subject has been beat to death. I apologize to everyone who groaned after reading my initial post.
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Old 04-07-2010, 04:19 PM   #3
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Sounds like your engine performed as designed. Duramax engines have two thermostats, only one is normally operating. When the coolant temperature rises beyond a set point, the second thermostat opens, allowing a higher volume of coolant to flow into the radiator. At the same time, the clutch fan engages, pulling more air through the radiator. Unless the temperature gauge hits the red zone you should be fine.
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Old 04-08-2010, 02:37 PM   #4
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Ray, thanks.

I got a little nervous when I found so many postings about the LLY overheating. In my research, I also discovered the "design flaw" in the intake mouthpiece of the LLY. I ordered a LBZ mouthpiece and will be installing it before my next trip to the mountains at the end of May. This modification should give me a little more HP and allow the engine to run a little cooler.
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Old 04-08-2010, 08:13 PM   #5
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Is this what you purchased? Duramax Diesel Performance Products by Killer Bee This man seems to be the expert on LLY over-heating.
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Old 04-09-2010, 07:55 AM   #6
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I read all of the materials on Killer Bee's site, although I could not follow all of his math, the concepts made sense. How I am going to address the problem, identified by KB, which is based on other blogs and postings, is to purchase the next engine generation's (LBZ) mouthpiece and marry it to the existing LLY air duct. Total cost - $95.

The next thing to do is to address getting outside air into the intake. Its hard to use the term cold air intake here in Phoenix.
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Old 04-20-2010, 09:29 PM   #7
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Killer bee lives very close to you. give him a call and have a visit.
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Old 04-21-2010, 01:47 PM   #8
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After doing a lot of research on Duramax forums, I decided to do my own upgrade of the LLY mouthpiece to the LBZ mouthpiece, $95.00 from GM parts online. I completed the work last Friday and wow, what a difference. Seems like I have a new truck. I also did my own "hillbilly" cold air intake. I put a 3" pvc elbow into the front of the air box and ran a foil dryer duct down to a toilet flange which is bolted to the back side of where a fog light would go (my truck does not have fogs). I then cut a 3" hole into the fog light area and viola! Cold air. I don't think the dryer duct material will last very long, so I'm looking for a substitute. It actually looks pretty clean and should work very well.

I'm doing the exact same trip as I did last month at the end of May. Then I'll know if the mouthpiece and cold air keep the engine any cooler. The only difference will be the outside temperature will be about 20 degrees warmer.
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Old 05-07-2010, 07:25 PM   #9
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Quote:
Originally Posted by marcusallen View Post
. I don't think the dryer duct material will last very long, so I'm looking for a substitute. .
Get the metal duct builders use for down draft cooktops. Its all metal. Most large appliance stores will have it. Home Depot nor Lowes had it even though they sell down draft appliances.
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