[jcollins23]

I have a 2000 Nissan Altima. I replaced my water pump and belts and flushed the cooling system. When I put it all back together and started it back up the engine got really hot. Everything was working before the water pump went out.

I’m assuming there is air trapped somewhere in the cooling system. However, I can't seem to find where it's trapped. I'm hoping the description below might at least help someone point me to where the blockage is, or possibly point to something else that's causing the problem.

Symptoms:
-Car starts at a good temperature when starting cold, but after a few minutes it overheats
-Air blows out when I turn on the heater but no hot air
-Car runs fine when I turn it on. No rough running or extra exhaust so I would tend to rule out any head gasket problems.
-I can hear the heater core motor running.
-Just before it's about to overheat, the radiator jerks around a bit like it's super hot. The upper radiator hose is boiling hot. The other hose going to the thermostat is cold (which I suspect is normal since the radiator would cool the water on its way down?)
-Both heater hoses are warm, but definitely not hot like the upper radiator hose is. The heater hoses don't feel like they have much coolant running through them.
-Occasionally while the car is idling the RPM gauge jumps up and down from 1000 to 2000. This does not occur when I have the flush n fill cap removed.
-If I take the cap off the flush n fill kit in the heater inlet house I see no coolant. If I run the car for a few minutes and it reaches operating
Temperature, some fluid sprays out periodically, but the interesting thing is is the temperature remains down. If I just keep adding fluid to the overflow tank, and let it shoot out the heater hose, the temperature stays down. If I cap off the heater hose again, after about a minute the car starts to overheat. Is this because the hot coolant can't get pass the heater core? This makes me think that the heater core may be plugged.

Actions take so far (all with heater turned on to max and blower on max):
-Replaced the water pump, pulley and belts
-Bled the cooling system 3 separate times following shop manual instructions (finally found the bleeder bolt and made sure it was open while bleeding).
-Took the water pump back off to inspect. Water pump looks fine and spins freely. Looked for any blockage in cooling hoses near water pump and found nothing blocking
-Changed the thermostat, making sure to install it in the correct direction.
-Replaced radiator cap
-Tried cracking open the flush n fill cap just a little but that still causes it to overheat.
-Flushed cooling system with thermostat removed and using one of those flush kits that attaches to the heater hose.
-Tried temporarily removing thermostat, no change
-Turned on A/C and the two radiator fans kicked in. When I run the heater on hot the two radiator fans only turn on if I've opened the flush n fill cap and let a lot of hot coolant escape for several minutes.

Questions:
-Could it be a clogged or bad radiator or heater core?
-What would you recommend I try next? I thought about disconnecting both heater hoses from the engine side and running the garden hose through one to see if it comes out the other end (should tell me if heater core is plugged?). Would attaching the garden hose also potentially clear the blockage?
-If this sounds like it could be a radiator problem, anything I could check on the radiator?

[this8384]

What led you to replace the water pump? Was it just because the vehicle was overheating or was it leaking antifreeze? How many miles are on the car? When was the last time you had the antifreeze changed? It sounds like the radiator is plugged up but I need more information to be positive.

[westnlas]

About the only thing you haven't done is to bypass the heater core. I would try that and see if that was it.

[jcollins23]

This all started when the bearing on the pulley that runs the water pump went out, and in turn the water pump went bad (leaking antifreeze). The car has 100k miles. I change the antifreeze at least once a year. In fact I think I changed it a month or two before all of this happened.

[jcollins23]

This sounds a lot like a stuck thermostat. You didn't use the old one when you replaced the water pump did you ?

No I replaced the thermostat. I even tried removing the thermostat temporarily to rule it out. Still overheated

[this8384]

I would try to flush out both the heater core and the radiator. It sounds like there may be some build-up in either of those components.