Friend with a issue... And Im clueless

Truck is 1990 Silverado with a 2004 Silverado's 5.3. The truck has a new water pump as in brand new. A SLP 160 t stat. Has a New 2 core radiator. And dual electric fans from a 07 Tahoe. The truck will run dead on 160 while in motion. BUT if say at a stop light or high traffic the temperature starts climbing... and doesn't stop. Till it over heats. He has tried flushing the system... He tried running the additive that is supposed to make a motor run cooler.... he has hit a dead end... And basically... everything i can think of he already has new... Anyone seen this before? Help would be appreciated...

Air is trapped in the heads. Park the truck on a hill, front end higher, remove the air bleed hose at the front of the head, pour coolant into the reservoir until a steady stream of coolant comes out of the head steam crossflow coming from the head.

You have verified the cooling fans are working of course? And blowing the right direction?

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Originally Posted by RedHeartbeat

Air is trapped in the heads. Park the truck on a hill, front end higher, remove the air bleed hose at the front of the head, pour coolant into the reservoir until a steady stream of coolant comes out of the head steam crossflow coming from the head.

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looks like youve had this problem :lol:

Think thats kinda like burping the system if not burped during fluid change right? cause air rights like a burp hints the name... Wonder if the fans are patched right in the tune tho?

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Originally Posted by Oldspimp

You have verified the cooling fans are working of course? And blowing the right direction?

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+1 Make sure the polarity of the fan isn't reversed. and make sure the fans are on the correct side of the rad.Another issue could be the 160 stat. It may not be slowing the coolant down long enough to cool it. I had that problem in my 3rd gen TA. Put a cooler t-stat and the sock fan wasnt strong enough to cool it because it didn't stop the water long enough.

Red I will try that as soon as he gets the truck back over here.
As far as fans they are installed properly and pulling air.... And very effectively at that. Once I verified fans were working correctly (also cant be the kicking on properly as they are hard wired to come on with ignition) I thought maybe it was the aftermarket t stat. But it was doing it before hand with the stock one as well.

Shoot different parts of the radiator with a temp gun. My 99 had the EXACT same prob and the radiator was clogged with mineral deposits. Something easy enough to rule out. I tried flushing it prior to the diagnosis and it didn't help.

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Originally Posted by AFSP1211

Shoot different parts of the radiator with a temp gun. My 99 had the EXACT same prob and the radiator was clogged with mineral deposits. Something easy enough to rule out. I tried flushing it prior to the diagnosis and it didn't help.

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I've mentioned this as well. Note he swapped to a new 2 core radiator. Thinking his original unit was messed up...

Never hurts to try. Drive up to the parts store and borrow one if he doesn't want to buy a temp gun.

Does he have a UDP? Is it possible that the water pump is going out? If he has a UDP its possible that the water pump isnt turning fast enough. Have you tried to hold the throttle at cruising RPM while the truck is sitting still to see if it still rises?

Make sure the belt routing is correct. The water pump turns the opposite direction as the crank.

Jeff

If he has a stall convertor, hopefully he has an auxillary cooler for it.

After I read the issue but before I read any responses my diagnosis was an air pocket. I have no issues with this any longer now that I vacuum fill these. The LS is so easy to get air locked because of the low tstat mounting.

I'll start with belt routing and move straight to doing what red said. Brand new pump probably less then 500 miles and isn't weeping out the weep hole... ( LS motors have weep holes right? Lol)