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1996 Impala SS LT1 running hot....changed water pump and sending unit...still running hot. Refilled with water and let air out of bleeder valve where radiator hose connects near intake. I did not flush the entire system. Should I? If so, what's the best way to flush cooling system? Any other suggestions on how to fix?

Thank you,
Joe
 

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Did you check the splines on the water pump shaft and the coupler? Have you checked the engine temperature with an external gauge or using a monitor connected to the OBD2 port?

Flushing the block is as easy as removing the radiator hoses. Remove the thermostat and then remove the knock sensors to drain the block. Then use your garden hose to keep filling the block until the water comes out clear from the knock sensor holes.

Have someone take a look at your radiator to see if it is plugged by sediment.
 
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You didn’t say if you replaced the thermostat. Could be stuck. Radiator could be clogged. Does the return hose get hot when the engine temp hits 180 degrees? It should.
 

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Did you check the splines on the water pump shaft and the coupler? Have you checked the engine temperature with an external gauge or using a monitor connected to the OBD2 port?

Flushing the block is as easy as removing the radiator hoses. Remove the thermostat and then remove the knock sensors to drain the block. Then use your garden hose to keep filling the block until the water comes out clear from the knock sensor holes.

Have someone take a look at your radiator to see if it is plugged by sediment.
Thank you....I appreciate your advice. Where are the knock sensors located? I agree and will look to flush out the block. Does the interior heater factor into water flow as well? Could this have an impact on the problem? I installed a brand new water pump and the splines look good when I installed. Whats do you suggest is the best way to flush out the radiator? Thank you for your time and expertise...very much appreciated.
 

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You didn’t say if you replaced the thermostat. Could be stuck. Radiator could be clogged. Does the return hose get hot when the engine temp hits 180 degrees? It should.
Yes sir...I did replace the thermostat. I also replaced the temp sending unit twice. What is the best way to flush out the radiator. I drained the radiator when I replaced the water pump however I did not flush it out. What is the best way to flush out the radiator? The hose on the top was hot when temp was 180 or higher.
Appreciate your help and expertise.
Thank you.
 

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Thank you....I appreciate your advice. Where are the knock sensors located? I agree and will look to flush out the block. Does the interior heater factor into water flow as well? Could this have an impact on the problem? I installed a brand new water pump and the splines look good when I installed. Whats do you suggest is the best way to flush out the radiator? Thank you for your time and expertise...very much appreciated.
The knock sensors are on the side of the block just above where the oil pan attaches to the block. They are removed from easily from the bottom from behind the cross member. Be careful removing as I damaged one when I removed the sensor.

Flushing the heater core is relatively easy as well, but make sure you do not use the full pressure of your hose as that will cause the heater core to fail. Generally you will reverse flush the core until you have a clear stream of water.

For the radiator, remove it from the car and flush with clean water until you see clean water exiting the radiator. Again reverse flush. You may be able to bring the radiator to a shop to have it cleaned. I personally replaced mine with a heavy duty multi-core all aluminum radiator from BeCool.
 

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Yes sir...I did replace the thermostat. I also replaced the temp sending unit twice. What is the best way to flush out the radiator. I drained the radiator when I replaced the water pump however I did not flush it out. What is the best way to flush out the radiator? The hose on the top was hot when temp was 180 or higher.
Appreciate your help and expertise.
Thank you.
The temperature sensor on the from of the water pump is for the PCM. The sensor screwed into the passenger head is for the dash gauge.

Test your fans to ensure that they are working. While the engine is running, unplug the temperature sensor on the water pump and both fans should start immediately. If the fans do not start, then you will need to check the fan relay(s).
 

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You can purchase cooling system flushes (like Prestone). These only really work on sludge, not hardened obstructions (minerals). Follow the directions, etc, etc. Marginal use.

The cabin heater line will not cause the engine temp to go red. Though a portion of heat is removed through that line, unless you are actually heating the cabin ... not really. Most of your heat is managed through the radiator.
See if you can look inside the radiator at the fin tubes Inside. If they aren’t really clear, consider replacing the radiator. How old is the radiator?

If you remove the top radiator hose and then pull the lower hose, the water should come out like a gusher. If it comes out more like a faucet ... it’s clogged.
 
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