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Discussion Starter #1
I've been forum trolling around looking for some answers to the problem but can't seem to figure the problem out.


I live in Mesa AZ so anytime we head out of town you are climbing out of the valley. Since summer is in full swing I avoid towing in the heat of the day due to the long hill pulls out of town.


I'm the original owner of a '06 Chevy LBZ with 188k miles. The truck has been great since I have owned it. But this has me puzzled. The truck is all stock other than one size bigger tires, so this is all from the stock gauge cluster. The truck since new would run ~195 degree normal operating motor temp, and 210 towing my 28' toy hauler that weights 8500 empty and around 10k loaded. When towing the secondary thermostat would open the motor temp would get up to 220/230, the fan clutch would kick on then the motor temp would come back down to 210.


In the last few months during the winter the operating temp dropped to 165/170 degrees. I thought it was from the cooler temps, but when towing the motor temp would come up to normal towing temp of 210 and when the motor temp hits 230 the fan clutch would kick on with the motor temp staying at 225/230 degrees. I don't like to see temps like that!


Since then I started with having the coolant flushed. Back in May I took a trip north towing and had the same results with low operating temps, and high towing temp. So a week after that trip I changed out both thermostats, and the temperature sensor with OEM parts. Since changing out the t-stats and temp sensor the normal operating temp is back up to 195 degrees, that was a good sign.


This past weekend the family and I headed north with the trailer for some cool weather camping. The ambient temp was 90 degrees during the drive and I tow around 60/65 mph. The first hill out of town is a long gradual climb, the motor temp came up to 230, fan clutch kick on, but the temp stayed. I backed it down to 2000 RPM, the temp came down a few degrees, but not like it should.


I have heard I should have the radiator pulled, cleaned or replaced since there is 188k on the truck. I haven't cleaned the bugs and road grime, could this be it? What else is there? New fan clutch? How hard are these to replace?
 

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Are you sure the T-stats were installed correctly? Mine was doing the same thing and then threw a code when it wouldn't get to operating temp. I changed the t-stats and realized the correct way to install them. Just a thought...

If you do change the clutch, I recommend using a factory replacement clutch, not aftermarket. I have always had problems with aftermarket clutches.
 

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You need to "CLEAN THE STACK" air has to go across the condenser, transmission cooler, intercooler and then the radiator. Bugs, oil residue and dirt accumulate and effectively block off flow. Most people never know just how dirty the stack is until it is taken apart to fix another problem. You can probably take the truck to a self serve car wash and spend a good amount of time spraying the stack being careful not to bend the fins. Pay close attention to cleaning the lower sections of the radiator and intercooler. Spray from grill towards engine and then from engine towards grill and use soap. The worst grime I have seen is on the driver's side down below the grill. Try to remove most of the bugs also, they impede air flow.
 
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Are you sure the T-stats were installed correctly? Mine was doing the same thing and then threw a code when it wouldn't get to operating temp. I changed the t-stats and realized the correct way to install them. Just a thought...

This crossed my mind, but since the temp was high before replacing the t-stats, and I made sure to install the secondary t-stat with the bypass towards the back of the motor I crossed that off my list.


If you do change the clutch, I recommend using a factory replacement clutch, not aftermarket. I have always had problems with aftermarket clutches.
Thanks for the info.
 

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Discussion Starter #5
You need to "CLEAN THE STACK" air has to go across the condenser, transmission cooler, intercooler and then the radiator. Bugs, oil residue and dirt accumulate and effectively block off flow. Most people never know just how dirty the stack is until it is taken apart to fix another problem. You can probably take the truck to a self serve car wash and spend a good amount of time spraying the stack being careful not to bend the fins. Pay close attention to cleaning the lower sections of the radiator and intercooler. Spray from grill towards engine and then from engine towards grill and use soap. The worst grime I have seen is on the driver's side down below the grill. Try to remove most of the bugs also, they impede air flow.

Ok I'll give that a shot. I was thinking I'd have to remove the stack to clean it. Thanks!
 

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Remove the plastic cover that blocks off the top of the radiator and intercooler. If you search around, you might be able to find a 90 degree head to fit on a wand to help clean the stack from in between the units.
 

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Remove the plastic cover that blocks off the top of the radiator and intercooler. If you search around, you might be able to find a 90 degree head to fit on a wand to help clean the stack from in between the units.

Ok. Thanks for the tip. I took a look at what I need to clean and was wondering the best way to get in there to spray it out. It would be really nice to pull the grill off too, but not sure what that will take.






I haven't much chance to dig into this due to work and family. I hope to work on the stack this week and test it out this weekend with a short tow trip up a gradual grade.
 

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I have just bought an 06 classic LBZ and on the first long up hill drag Temps got a bit high before the Bimetal clutch fan kicked in. I felt it was a bit high compared to my older gm. So off came the shields and I cleaned the stack. Then I remembered I had a similer problem with a 6.0 that turned out to be a dirty BImetal actuator on the fan. Remember it faces forward to the stack, and will build up with crud and needs a bit of care. I removed it cleaned and lubricated the the device. Problem went away. By the way you can test it on the bench by using a propane torch (very carefully) to watch the action. And most important don't lay it flat for long. Keep it vertical like it is in the truck. to keep the viscous fluid (silicon gel I think) from leaking to the wrong side.
Sorry for the long comment. Be safe Be happy
 

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Discussion Starter #10

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Thanks. After reading 19 pages I think I'll be tearing the stack apart on this long 3 day weekend. Seems like all the symptoms listed are exactly what I have and should cure it.
Might be a good idea to schedule someone to help, just in case. I went to do mine (still have not done it) and realized lifting the radiator and intercooler in one unit is to much for me, if I was a silverback gorilla no problem. I believe you can separate them while still in the truck just never did it.


One other suggestion, when you pull the lower radiator hose be sure and push on the hose fitting to release the tension on the bail clip so you don't mangle it. Before you reassemble that connection remove the O-ring flip it around and put a light coat of silicone grease on it.

IIRC some Oreilly stores and NAPA's have the O-ring if yours fail to seat.

Bail clip for the hose end, GM part # 2580-6515

O-ring silicone 70 Durameter -226 (2" ID, 2 1/4" OD by 1/8" width) O-ring. I bought a package of 10 for $5.46 from McMaster-Carr (PN 9396K217)

Here is good thread with some pictures of why I had to replace my radiator hose and about the best way to remove the coolant.


http://www.dieselplace.com/forum/76-speciality-forums/64-maintenance-fluids/594554-radiator-flush.html#post6375970
 

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If cleaning the stack doesn't fix the issue, you may need your radiator looked at, as you mentioned in your first post. I had similar issues where the coolant temperature would rise very quickly when going up hills under load and took a long time to come back down. I tried cleaning the stack, but there really wasn't much in there, and it didn't fix anything. I ended up taking it to a shop, where they determined the radiator was 40-50% full of gunk, so I only had about half the cooling capacity. I had them put on a Hayden fan clutch at the same time to make sure the problem didn't recur, but I think the radiator cleanout is what really made a difference for me.
 

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When the radiator is out, look in the bottom for sediment. Radiators clog from the bottom up.
 

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Discussion Starter #14 (Edited)
Since I had a long weekend I decided to tear into the stack. Friday night I did as much as I could to get a head start before the heat hit on Saturday morning.


Friday morning I figured I might as well replace the lower hose since I'm going this far, and there is a 189k on the hoses. So first thing Saturday I drained the coolant. I took the radiator and the intercooler out as one unit. As you can see from the picture the radiator was bad. I'd say 60% was blocked. 4 cans of degreaser for everything and an hour of pressure washing everything looked way better.


While letting the degreaser soak I pulled and replaced the lower hose. I noticed on the right side of the frame there is a hose and clamp that the radiator hose would rest on. I took some 3/16 rubber I had laying around and cut a 1" strip that would wrap around the new lower hose and zip tied the rubber to the new hose. Pour design by GM to have a major coolant hose resting on a metal clamp.


Since I had the truck apart I cleaned up a few other things, replaced some of the plastic shields that go around wires etc. I took my time and had everything back together by noon. I think the total time to do this was 6 hours. Longer than what was posted it would take, but I did a few other things while it was apart.


I took the truck for a test run, but believe I still have some air in the system. I thought I had it all out with the bleed bolt at the thermostat. But the early signs show the temp is better. The air temp was 105 so as expected it would run warm. I'll take it out again this week after some commutes around town to make sure the system is air free.


A couple things I found that wasn't in the DIY forum post link, is remove the air cleaner platform that sits above the lower radiator hose. This gives a lot move access to work and is only 5 bolts. When you move the AC condenser out be sure to put something soft between the condenser and the mount for the tranny cooler. I did some damage to the condenser, but nothing major. I removed the radiator and intercooler as one unit, but when I reinstalled it I did them as separate units. With the air cleaner platform removed it made it easier to assemble the 2 units back together. One last thing, if you have a cordless impact this made life a lot better.
 

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