Heater hoses looped? If not, have you tried pinching off the heater hoses and see if it changes?

Sometimes looped hoses or a heater core with little restriction will let hot coolant recirculate and never hit the radiator.

 

If you're going to coat it, i'd use mild steel.

 

Mine are run through the heater core. Since its summer and I don't see me using the heater for awhile Ill give that a shot. Is it ok to just cap both heater hose ports on the water pump or do I need to loop them?

 

Is the gauge correct? Have you bled the air out of the system? Easy way to get the air out if you have an overflow tank. Get a full gallon of coolant, take this hose off the overflow and put it in the new gallon of coolant. Make sure the radiator cap is on. Run the engine until it’s gets hot (200ish) and shut it off. Let it be. As it cools it’ll push the air out and suck the coolant from the jug with the hose in it. Works like a charm. Good luck.

 

You can cap them or put an inline ball valve to stop the flow.

 

Gauge is correct. I have 3 different temp gauges lol. One for the holley HP, one for the factory gauge, and one auto meter in a little triple gauge pod under the dash. All three gauges are within 5 degrees.

I have bled the air every possible way I could think of. Filling through the top of the water pump, filling the radiator and removing a steam vent and letting coolant purge out. Filled the overflow tank full and let it get hot.

The truck is awesome when driving. It runs super cool temps but as soon as I stop it just climbs fast. I'm about to the point of changing radiators, water pump, and fans but everyone keeps saying that they have no issues with there similar setups.

 

If it’s got an aftermarket water pump, I’d start there. Go online and look for a “new take off” gm water pump. Plenty out there and proven.

 

Make sure your fan is blowing in the right direction. Any chance you got a reversed flow pump?

 

Fans are both pulling, The water pump was on the motor when I got it. Its a 2006 yukon denali motor so I wouldnt think it was a reverse flow bu who knows.

 

So I tried the heater core bypass with the little U shaped hose and that did absolutely nothing. I even bought some DEI reflective wrap and wrapped two of the temp sensors thinking that maybe they were just getting hot at idle with no airflow. I lost a little coolant from installing the heater core bypass so when I went to add the coolant I looked down in the radiator and could see that the water pump is moving coolant. Is it moving enough? hard to tell....

So what would you replace next?

Radiator or water pump?

Radiator is a single pass 4 core. with (2) 12" fans. Its a cheap aluminum one I bought off ebay a few years ago when I had the 383.

Water pump is some aftermarket brand that was changed by the previous owner. Most likely a cheap autozone special.

 

Will it cool down if you raise the engine rpm at idle?

 

That's a tough one. I've never seen an LS that won't cool if it was burped. Hard to beleive it gets hot that fast. My LS1 Firebird would take forever to get hot enough for the fans to come on when sitting at idle, like 15 minutes.

 

I hadnt thought about trying that. Ill give it a shot a cruise night tomorrow. It idles at 900 so its not super low, but that could tell me if its the water pump not moving enough volume.

 

Im leaning towards the water pump. It has to be a low flow condition. to many people are running similar or worse radiators than mine and not having issues.

 

Can you post a pic of the belt routing?

 

I will try to get a good picture. I did check the belt routing to make sure it was not running backwards.

 

Crank turns clockwise as you look at it. WP turns counter clockwise.

 

As long as the back of the belt, or the smooth side of it is what is running the water pump, and the rib side is on the crank, its turning the correct way. Actual belt routing doesn't matter for direction.

 

Well truck is still over heating and I am getting really frustrated.

Today I installed a brand new AC Delco water pump (pricey little boogers) and new 16psi radiator cap. I have the heater core completely bypassed and when I filled the truck with coolant this evening I jacked the back of the truck up so the engine was level. Filled the engine with coolant through the top of the water pump outlet, removed the front steam vent and let the air purge out that way. left the cap off and and ran the engine till it reached 195 degrees so the thermostat was open and topped of the coolant again. Let the truck cool down to ambient temp (97 degrees today) installed the cap and started the truck. The truck reached 240 degrees in about 10 minutes. I left the hood closed to simulate being stuck in traffic. I have confirmed that the water pump is spinning the correct direction and that the belt routing is correct. I wrapped both the holley and the factory gauge temp sensors with heat shielding and wrapped every bit of exhaust and hot side with heat wrap.

The only thing I have left to replace is the radiator. Its an aluminum 3 core single pass with (2) 12" fans (no shroud). I have confirmed that both fans are "pulling" and both are working. Drivers side fan is at the top of the radiator and the passengers side fan is at the bottom. Both fans are mounted as close to the suction and discharge side of the radiator.

It has to be either the radiator, no radiator shroud, or that the under hood temps are just so hot that its causing the sensors to get hot and give a false reading. After I shut the truck off I shot the radiator inlet with a Fluke temp gun and it read 175 degrees.

If there is anyone that can help please let me know! If you can help me solve it ill send you a bottle of crown (dead serious).

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Measure the radiator and give me the dimensions. I’ve got a couple here. We can work something out if I have one that’s close. BTW, the hotside radiating heat to the upper hose isn’t helping. Also, try putting a thermostat in the radiator (stick it done on the coolant with the cap off) and monitor temps. The fact that you said it got to 240, but the radiator measured 175 causes concern. Shouldn’t be that big of a difference.