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5.3 V8 New Water Pump/Thermo Install. Now Overheats

5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby rayson [OP] » Sep 15 2020, 9:06pm

2005 GMC Sierra 5.3 liter Vortec with 130K miles.
So I decided to replace my leaking water pump myself. I bought a Gates water pump with a new thermostat already attached. I couldnt find a drain plug at the bottom of the radiator so I just disconnected
the lowest hose (which is the one on the passenger side of radiator) and drained it. Also, I disconnected the two heater core hoses and took off the old water pump alot of the rest of coolant came out. I put everything back together and refilled with dex-cool 50-50 through the overflow tank. I put about 2 gallons in which I thought the capacity is about double. I drove around and at first looked steady at about half on the temp gauge but then gradually went all the way to hot. My dash will say engine coolant hot. After letting it cool, I tried to put more in but it only took about a 1 1/2 cups.
I cant drive around for more than a mile or 2 before the gauge goes to extreme hot. I tried setting the cabin temp to hot to allow the coolant in through the heater core. What am I missing? Is there still air in the system? How do I get it out? Is the thermostat working? Is it not letting the coolant through? Is something else stuck in my system and not letting the coolant through? Videos online make it look so simple. Just replace bad water pump, rehook everything, and refill truck with coolant. I've done that but my truck overheats. I've looked around carefully and nothing is leaking. Any help or tips is appreciated!
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby Walkers » Sep 15 2020, 9:54pm

Was the thermostat in the correct direction? Did you burp the top radiator hose?
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby rayson [OP] » Sep 15 2020, 11:30pm

I honestly didnt look closely at the thermostat. I figured the manufacturer (Gates) wouldve put it together already correctly, since it was already bolted to the water pump.
Burp the top hose? I didnt but that seems unusual and not mentioned in any videos I've seen. How do I do that?
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby silentbravo » Sep 16 2020, 1:58am

I thought these trucks had closer to 4 gallons of capacity, so more than likely you have a big air pocket and need to get more coolant in there.
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby Scrapyard John » Sep 16 2020, 3:05am

I would definitely pull the thermostat and check and make sure it’s facing the right direction. If it is facing the correct direction, test it in a pot of boiling water (or just replace it).
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby Nosaj90 » Sep 16 2020, 6:10am

Hi it sounds like you do not have enough fluid. Mine took more than 2 gallons.
Repeat what you did from cold but back off the pressure cap and run it at idle turn heater to hot and let any air escape. Cycle the heater hot / cold whilst idling to make sure any trapped air escapes.
Good luck.
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby rayson [OP] » Sep 16 2020, 9:26pm

OK topped off the reservoir tank with a little coolant. Started the truck cold. I put cabin temp to hot. I left the cap off the reservoir and watched as the truck got warm. I was hoping for bubbles (air out) but instead the coolant started rising in the tank and out the overflow tube so I closed it. Drove it around and after about a mile, starting going past the mid-mark to almost hot again. So tomorrow, Im going to drain the coolant and pull out thermostat and test it in boiling water.
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5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby tortuga13 » Sep 16 2020, 10:35pm

Did you save the original thermostat? I would reinstall that one and see if the overheat persists. Have you verified that the radiator fan is coming on correctly?
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby rayson [OP] » Sep 16 2020, 11:34pm

I did not save the old thermostat. Yes, radiator fans do come on when the temp needle approaches hot.
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Re: 5.3 V8 New Water Pump/Thermo Install. Now Overheats

Postby rayson [OP] » Sep 18 2020, 5:50am

I took out the thermostat and put it in boiling water. It opened. I decided to buy a Stant thermostat anyways and see if putting a different one will make a difference
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