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Discussion Starter #1
My '05 has recently started running very hot when towing over mountains. My mechanic mentioned that maybe the radiator was full of sediment and needed to be replaced. If I end up going that route is there a better, higher cooling capacity radiator that would be a direct fit? I'd rather upgrade a bit then just put another OEM radiator back in .
Also, what else should I check? I know LLY's are known for running hot. I've owned this truck since new, put 252,000 miles on it. I've been pulling loads over this same mountain for years and it never got this hot this fast before. The gauge pegged and I got the "engine overheated" message on the DIC. This was with the AC off and the heater running in the cab.

Thanks,
 

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I have the Ron Davis main radiator and aux. The main radiator is a direct fit with more capacity. However, if it all was fine before and it truly is a clogged radiator (totally possible at this age) why change to something bigger and more expensive? If you take it out and look in the bottom (where the clogging starts), are the tubes covered in sediment? It may be as simple as a new stock radiator.

Beyond that, check the cooling fan clutch. Did it engage? Also, did the trans heat up too (adding heat to the system)?

As for the aux, again, if something changed, fix what changed. If you just want more capacity, then either the Ron Davis aux or the main radiator is where I would start. Frankly, I would install the aux first and only add the main radiator if the stock one was going south AND I had the extra cash to do it. I am not sure of the current prices but $2000 for the pair wouldn't surprise me.
 

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You should also remove the radiator and intercooler and clean them out. Debris gets stuck in there over time reducing the airflow and cooling. At that point you can check the radiator too.
 

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Why don't you just upgrade to an LBZ radiator, fan shroud, fan and fan clutch for a 2006-2008. LBZ's never had an issue with running hot, there all factory parts and will bolt right in
 

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No, I believe you can push an LBZ to overheat but they are certainly far better. There are LBZs that installed the secondary radiator.
 

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From what I understand the LLY equipped trucks had the smallest radiators out of all the Duramax pickups. Which is one of the reasons why the LLY's tend to run hotter.
 

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I thought the LB7 was the same and that was the issue. They cranked up the power with the LLY but didn't increase the cooling capacity. Alas, this has been beat to death.
 

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Why don't you just upgrade to an LBZ radiator, fan shroud, fan and fan clutch for a 2006-2008. LBZ's never had an issue with running hot, there all factory parts and will bolt right in
Are you certain the LBZ radiator will bolt into an LLY? I am getting ready to pull my engine and Plan to replace a few things as I reassemble. I'd like a larger capacity radiator as I always upgrade when possible.

I was under the impression that the LBZ radiator was taller, used a different support, and needed the taller hood for clearance. Not true?
 

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Loader, from what I read over the years, my understanding the same as yours, that it won't easily fit (or not at all).

engineer837 made something (using Ron Davis, I think). Mishimoto might be good, too, I don't know. Either way, some of us believe an aux radiator is the only real solution keeping the LLY temps in check.
 

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Why won't it fit? It's the same exact truck, same body style, same everything. The only difference is one is an LLY and one is an LBZ, and even that the engine's are very similar.
 

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Loader, from what I read over the years, my understanding the same as yours, that it won't easily fit (or not at all).

engineer837 made something (using Ron Davis, I think). Mishimoto might be good, too, I don't know. Either way, some of us believe an aux radiator is the only real solution keeping the LLY temps in check.
Why won't it fit? It's the same exact truck, same body style, same everything. The only difference is one is an LLY and one is an LBZ, and even that the engine's are very similar.
 

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Why won't it fit? It's the same exact truck, same body style, same everything. The only difference is one is an LLY and one is an LBZ, and even that the engine's are very similar.
The LLY & LBZ are GMT800 trucks but after that there’s not much similarities.
It has been done but it’s costly.
https://www.duramaxforum.com/forum/04-5-05-lly-duramax-powertrain/103416-difference-between-lly-lbz-cooling-systems.html
It’s best to Google (duramax install an LBZ radiator and cooling system on his LLY) you will get a lot more info than on here.
 

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Start with the cheapest first........clean your cooling stack! You'd be surprised how much crap comes out of there. Rad, intercooler, AC condensor, Trans cooler. Clean em all.

The fan clutch only works if the air can pass through the stack, and hit the fan.



Sent from my LM-G820 using Tapatalk
 

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Discussion Starter #16
My mechanic installed a T in the little line that goes from the top of the radiator over to the expansion tank. He ran a tube from this T into the cab to a pressure gauge. He told me to watch the gauge and see if I'm building any pressure. Just driving around The gauge only reads maybe 1 to 3 psi. Going up a mountain with the truck loaded to about 11,000 pounds it gets to about 3 or maybe 5 psi.
Today I hooked up a trailer with a Bobcat on it and went up and over 2 mountains twice. I had as much as 14 psi on the gauge. My temperature gauge climbed from 185 to about 240. This was with outdoor temps around 35 degrees and raining. I had the heat on in the cab.
I tried to call my mechanic and get his opinion on the numbers but I was unsuccessful today. I looked at the cap on the expansion tank and it's rated 15psi so now I'm thinking I'm within the pressure limit of the cap so maybe it's fine.
Anybody got any opinions on any of this.
And no, I haven't done anything else to the radiator yet. The truck does fine unless I'm towing and I've had too much work the last couple months to tear the truck apart.
 

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Take the radiator and intercooler out and look. Look in the bottom inlet of the radiator and see if you have a lot of sediment. If so, it’s clogged and should be replaced. Clean the radiator (if you don’t replace it), AC evaporator and intercooler fins. Reassemble and test.

At this point, you aren’t going to discover anything new short of leaking head gaskets. If your upper hose isn’t hard after sitting over night you probably don’t have bad gaskets but a soft hose don’t mean they aren’t bad. A hard hose is pretty conclusive they are bad.

That tank is a surge tank and it’s at the same pressure as the radiator. Towing heavy and getting pressure in the tank/system is totally normal. It’s not a recovery tank. It says right there on the cap “Don’t remove when hot if you value your skin and face!”

Ok, I paraphrased ... :)
 

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Why won't it fit? It's the same exact truck, same body style, same everything. The only difference is one is an LLY and one is an LBZ, and even that the engine's are very similar.
I checked with a Duramax shop to be certain. It won't fit without significant work - better said, it isn't a bolt-in replacement. The radiator is larger. The LBZ trucks have a different core support. The fan, fan clutch, and shroud are all different.

If you have a LBZ doner or want to go new, then you could. But, I don't think the LLY hood will clear the LBZ core support either (I haven't been able to verify this yet).
 

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What they said...

I had tranny problems, and at first I was convinced it had to do with the trans cooler... so I replaced it. When it was off, I took the time to clean the stack; the stack was so full of crap immediately behind my trans cooler, it was amazing there was any airflow AT ALL. I shot a couple cans of degreaser throughout the stack, let it sit, and sprayed it off/out with a garden hose. The stuff that came out was nothing short of disgusting. I'm certain there's more stuff there, but I was able to get most of it out. Turned out it didn't change anything for me; my transmission was shot. Oh well...

In order, I'd:
  1. Clean the stack thoroughly
  2. Look for crud in the radiator and consider replacing it if it's clogged
  3. Consider trading your truck for an LBZ
  4. Think about replacing the LLY radiator with an LBZ radiator
Good luck!
 

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I may be out of touch or misinterpreting the answer to the question. If the radiator has sediment cant you take it to a radiator shop and get it rotted out? I have 303k on my truck...runs good. A installed the NAPA coolant filter with success...
 
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