My 2005 nissan sentra is still running hot, just replace the thermastat, what can it be/

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Sounds like the heater - ac door actuator is not working. This part would need to be replaced, it's not repairable.

Hello again
The problem here based on what you have told me is that you have a cylinder head gasket leaking combustion gas into the cooling system, this creates gas pockets around the thermostat and delays it opening. You can try adding one of the many head gasket sealers available in auto parts stores. I suggest you contact a local NAPA or Carquest auto parts store and ask what they think really works, I' heard that many do work but have no 1st hand knowledge. To make sure air is not in the cooling system do the following, you will need a floor jack. If the problem persists you will need the head gasket replaced and the cylinder head checked for cracks and if it checks ok then machined flat again.

The generic method of bleeding air from the cooling system is to use a floor jack and raise the front of the car as high as possible, then fill the coolant recovery tank full and run the engine until it just starts to overheat, high end of normal zone on gauge, then shut the engine down and run cold water over the radiator core, this will self bleed the system and the coolant will be pulled from the recovery tank, repeat as necessary, never let the recovery tank run dry or more air will be pulled into the system.

has to be air bound.with vehicle running but before it gets too hot remove outlet hose from heater core at bulkhead.wait for consistant waterflow out of hose then reinstall and top up system.now the bad ....where did the air come from?these engines are becoming notorious for head gasket failure.does it ever miss and run rough for fist few seconnds after a cold start?if so this is probably your issue.

just replace the water pump.it does not run with timingbelt

right underneath the end of the top radiator hose in a small housing unit with two bolts

there is a set scre usually allen head that you can screw out and then the plate will slide up and off

If all of the things you replaced are working fine I am going to say double check the thermostat. Also make sure your fan is engaging at temp. You cam check by running till warm and then running the AC. If the car does not overheat with the AC on then your fan is not running under normal conditions (with AC off) This can be caused by a couple of different things depending on how the fan is set up. I am not a nissan expert

Hey iisha, although obvious, 1st thing to check is the coolant level. If it's low, the engine will run hot and the low level prevents coolant from circulating to the heater core inside the car, so the result is little or no heat, but engine running hot situation. The top rad. hose takes hot coolant from the engine, it flows down thru the radiator where it is cooled (w/ help from the fan) and the coolant returns to the engine at a reduced temp. to keep the temp under control, and it's returned thru the bottom hose (the result is the bottom hose should be cooler thant the top. There's more involved than that, so 1st check your coolant level, if it's ok let me know I'll help further. Hopefully the fix is that simple, and it is a rather common problem.