I drive 4 or 5 miles and the temp. gauge goes to about 3/4 to just below 260
the reservoir fills up and bubbles. After it cools the reservoir is near empty.
I've had the thermostat replaced and the fans are both working and the radiator flushed (and made sure that there is no air in the system). There is no water in the oil. There do not appear to be any leaks. I've had two mechanics look at it several times and they've run out of ideas. ( One did say a new water pump might help)
Any thoughts would be much appreciated !!!!!!

yea it could need a water pump, you had it pressure tested for leaks or does it appear to have none?

At 260° and steam flashing off in the expansion tank, I'd guess that there was adequate pressure. Still, a test would be a good idea, both with a dead cold engine and fully hot one. A compression leak into the cooling system via cracks around the valve seats or spark plug holes, or a failing gasket, may not show up on a hot engine, but can on a cold one.

As suggested, checking the coolant flow would be a good idea. A slipping or eroded impeller on teh water pump shaft could be a problem, as well as restriction in the lower hose or within the radiator itself.

"a test would be a good idea, both with a dead cold engine and fully hot one."

Good idea. Thanks. I'll try it.
Also, I bought a new radiator cap. We'll see if that helps.

"a test would be a good idea, both with a dead cold engine and fully hot one."

Good idea. Thanks. I'll try it.
Also, I bought a new radiator cap. We'll see if that helps.