doug c

That's about what I thought. I know the radiator is fine, because it is hot as weel as as hard as the top hose, and when I squeeze it with the cap off I can get the coolant to gurgle out of where the cap was. So if I assume the new thermostat was not defective, and I trust that the mechanic is correct when he said he was sure the spring was facing the right way on the thermostat, then where am I? How can I determine that the water pump is pumping? I have visually inspected the pump and it seems tight and the shaft is turning, but can the system be flow tested somehow? And I am doing as you suggest....a half a cup here, quarter of a cup there....

994 Es300 with 288,000 miles. I have found when buying parts that this was probably a 2003 engine in a 2004 model year, as it was built in november of 2003. Therefore, it has the single hydraulic powered engine fan instead of the twin electric fans later that year. In the hot (80 + Fahrenheit) weather it starts to run hot. If I keep speed to under 70, and AC off, it will run for an hour or so and then start to creep up. Turning the heat on will bring it back down, at which point heat can go off and all is fine again for another 30 or 40 minutes. Any time the AC is turned on the car will go up towards hot...after about 10 or 15 minutes. I have recently flushed the system, and replaced the thermostat. The coolant flushed out looked brand new, the thermostat seemed fine, although while out it was replaced. I find that the upper radiator hose is very hard when the car is warmed up. It returns to normal pressure when it cools off. I don't see any evidence of a head gasket problem. The oil is not milky, there as been no coolant loss, no smoke from the pipe, etc. The heat works fine, so I suspect the water pump is functioning. Any suggestions? Also, How do you deal with airlock in the cooling system. I see it refered to in several heat related posts.

1994 Es300 with 288,000 miles. I have found when buying parts that this was probably a 2003 engine in a 2004 model year, as it was built in november of 2003. Therefore, it has the single hydraulic powered engine fan instead of the twin electric fans later that year. In the hot (80 + Fahrenheit) weather it starts to run hot. If I keep speed to under 70, and AC off, it will run for an hour or so and then start to creep up. Turning the heat on will bring it back down, at which point heat can go off and all is fine again for another 30 or 40 minutes. Any time the AC is turned on the car will go up towards hot...after about 10 or 15 minutes. I have recently flushed the system, and replaced the thermostat. The coolant flushed out looked brand new, the thermostat seemed fine, although while out it was replaced. I find that the upper radiator hose is very hard when the car is warmed up. It returns to normal pressure when it cools off. I don't see any evidence of a head gasket problem. The oil is not milky, there as been no coolant loss, no smoke from the pipe, etc. The heat works fine, so I suspect the water pump is functioning. Any suggestions?