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Discussion Starter · #1 ·
I have a 2004 2500hd with the LLY It has been overheating so i put new thermostats in it, new water pump, and head gaskets. After all that it is still overheating it will run fine at idle and have no heat, once you drive it down the road and go over 35 it will overheat very quickly, after that i put a radiator in it and it seemed to help it only overheats driving down the freeway at 70 mph but i still have no heat but once i stop it will go back down to just under 210. I followed the special fill procedure on the gm website and i have put about 100 miles on it trying to get any air out of the system. PLEASE HELP
 

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AKA treyfox11
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switching to the lbz mouthpiece will help your problem tremedously
 

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Have you checked your coolant reservoir cap? The vent hole could be plugged and possibly causing problems. Also make sure the radiator hoses aren't being sucked flat. You might fill out your sig so people can see what mods, eqpt etc you've got....
 

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Well first what about an oil cooler! They go out easily! Check it!
 

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Maybe you have a collapsed rad hose or something, If you dont have any heat in the cab when your engine is heating, its a coolant flow/airlock problem PERIOD. Not a mouthpiece problem. See if you can rig a flow meter on it or something to try and pin it down to whats going on. Also, is the gauge accurate? Use a IR temp gun on the engine.
 

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No question about it you have a lack of coolant flow... once the truck get hot carefully see if the upper and lower hoses are hot. Also check to see if the hoses are collapsed or very pressurized. Also had a similar problem with my truck when plowing, ended up being the fan clutch, it was never engaging. Before doing the fan clutch I also did hoses, radiator, thermostat, rad. cap and tested the water pump!
 

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May have to backwash the heater core
 

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No question about it you have a lack of coolant flow... once the truck get hot carefully see if the upper and lower hoses are hot. Also check to see if the hoses are collapsed or very pressurized. Also had a similar problem with my truck when plowing, ended up being the fan clutch, it was never engaging. Before doing the fan clutch I also did hoses, radiator, thermostat, rad. cap and tested the water pump!
There you go...... does the fan kick on and roar like a freight train a lot? If not, it should be...... check the fan.
 

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a PLUGGER HEATER CORE will cause the same problems
 

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Discussion Starter · #15 ·
I have also replaced the radiator cap and when its running the upper hose gets real hot but doesn't get firm and sometimes when you shut it off and let it sit i can go back to it and the upper radiator hose will be collapsed. also i opened up the coolant jug after running for about an hour and the coolant was still ice cold so that tells me that either my new water pump is not working the way it should or there is still some type of blockage.
 

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The upper hose being collasped is caused by a stuck valve in the coolant cap. They can usually be cleaned.

I agree that you may have a water pump problem-- there may be a problem with the housing that the pump set in-- corroded or damaged. You need to remove the hose and check for flow. Someone had a impeller that came loose- so it was not turning.
 

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Check/Replace your thermostats, I see that you did but i have bought new ones that havent worked before, just a thought
 

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just my 2 cents make sure the heater core plastic adapters are not comming apart for the inlet side they usually get like a brown burnt color and then start breaking and then pluggs the heater core
 

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Yes try flushing the heater core. Pinch off the hoses going into it so u dont lose a bunch of coolant then flush it out with a garden hose and or a blowgun on an air compressor, this happens all the time.
 
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