04 sentra 1.8 over heats after a highway drive. Pull off the highway and come to light and needle shoots to just under H! Start to drive and needle drops right away. Changed thermostat, did two rad flushes. Intermittently blows heat more heat at 40kmph than 100! No residue in oil, no white smoke and bottle gurgles after shut off. Hard start when hot too! Related? Water pump?

Some "heat soak" after a run is normal but yours sounds excessive. I would look at the electric fan operation, either failing to come on when temperatures rise, or not cooling enough due to debris in the rad or A/C condenser. The rad flushes you did no doubt helped this situation to some degree. Listen for the fan to come on next time you pull off the hiway. I assume "bottle gurgles" refers to your coolant overflow reservoir. It should be kept full until you're sure all the air is out of your system after the last rad flush. I hope some of this helps, .... Dennis

When the engine begins to warm, how long does it take to reach operating temperature? Can you hear the fans running? If the fans are running, warms pretty fast, replace your waterpump. Whats happens is the impellors begin to corrode in the centre and become dislodged from the shaft or in some cases break apart. The reason it will not consistantly blow heat is due to it boiling and the heater circuit is most suseptable to air bubbles so once it calms down, you get heat. It would also be a great idea to replace the radiator cap also. Let me know if you need anything else.

Air pocket need the thermostat housing.

Air is not a good conductor of heat.

Park you car on a hill and let the air pocket to work itself out to the cooling system.

A shop will charge $65+ to purge the air out.