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Juicifer

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Hey guys, i figured id throw this on here just in case anyone has been in my shoes before. I have a 95 tahoe 5.7L. Replaced the water pump 3 weeks ago and recently the truck will run really hot for about a minute, then its as if a valve opened or something was blocking coolant flow b/c then it will just drop back down to normal. I changed the thermostat and still no fix. Could it be the radiator? I'm also not getting hot air out of my vents.

Took it back to the mechanic that changed out my water pump and they aren't really sure either. their only suggestion is to try to change the radiator.
 

east302

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I would start with a good coolant flush.

How does the belt look? Tensioner tight?

Are the radiator fins (or whatever they're called) flattened? Any crud or obstructions on the radiator?

I've heard of a fan clutch causing overheating, that may be something to look into.

Are either of the two heater hoses getting hot where they go into the firewall?


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HiHoeSilver

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Could also be an air pocket. My 5.7 had a little leak about halfway up the radiator, so it wouldn't hold coolant capacity for more than about a week. When it got low enough that had some air pockets in the lines, it would do exactly as you're describing. The needle would steadily climb up almost to the red, sit there for a minute, and then drop like a rock to normal operating temp.
 

east302

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HiHoeSilver makes a good point. Do a pressure test on it and see if you have a leak.


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Kenny D

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Most likely it has air in the system. Although it should have purged itself by now if you have been driving it.
 
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Juicifer

Juicifer

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hmm ok interesting. I changed the radiator and drove it again. Still running hot, but then it will go back down. so eventually it should naturally purge the air through? is there any chance the cpu is just freaking out and causing my gauges to act up?

thinking of taking it to the stealership just to see what their opinion will be...
 

east302

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To purge the air, start the engine cold with the radiator cap removed. When the thermostat opens (upper hose gets hot), the level should drop and air bubbles will come up. Add coolant up to the bottom level of the radiator neck.

They make a special funnel for it as it can be messy as the bubbles come up.

Skip to about 16:30 in the video...



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Kenny D

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Any time I have ever messed with the coolant on the 5.7, before I install the thermostat and housing, I make sure the lower hose and heater hoses are connected and then I fill up the engine with coolant through the intake until it is just about flush with the themostat opening. Then I install the thermostat and the housing. That way at least I know that the engine is full. That way the radiator level is even with the highest point of the engine. The only air that should be left is in your heater core and the rest of the radiator. Once I finish topping off the radiator, then I start the engine and let it warm up and top it off again. Usually have to add a little bit more after a few trips into town.
 
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Juicifer

Juicifer

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Update:

I purged the air out and it worked. my engine ran nice and cool just like normal. i drove it around for about 20 mins and still everything was normal. unfortunately, when i started the truck up the next morning i heard loud clacking noises coming from the engine. heads i'm assuming. the damage had been done. idk, i asked the shop that replaced my water pump about it and they said they purged the air too. all i know is i have to replace the engine now.

has anyone on here done an engine upgrade? if i'm gonna do this i might as well put something better in there. suggestions?
 

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