1996 Cadillac Eldorado ETC: Overheating Problem

[96CadillacEldorado]

Hello,

I am looking for help to solve an overheating problem on my 1996 Cadillac Eldorado ETC.

The car reaches operating temperature in a normal amount of time. It Does not leak coolant or overheat while idling. It does not leak coolant or overheat at freeway speeds. However, the car does leak coolant and then overheat in "stop and go" traffic or areas with frequent stops or red lights. The overheating is caused by a loss of coolant leaking from the expansion tank outlet hose. If the car is refilled with new coolant, it returns to operating temperature. My question is what causes the coolant to leak out of the expansion tank outlet hose?

RECENT REPAIRS:

Heater Core

Radiator

Radiator/ Reservoir Cap

Thermostat

TESTS:

Cylinder Compression Test (all 8 cylinders at approximately 160 psi)

Coolant Pressure Test (maintains 16 psi of pressure for a long period of time and no visible leaks)

Cooling Fans (both fans are in working order)

Water Pump (circulates coolant throughout the engine)

MISCELLANEOUS INFO:

No white smoke comes out of the tail pipes

Smooth engine idle

No milky oil

Clean Dex-cool antifreeze

[barczy01]

When the car is cold the expansion tank should be only be half full. I am sure you have a good 50/50 mix of coolant and water. I am looking over what you have done to the car and I don't see a block test anywhere.

[winterset]

Also check the engine side of the tube leading to the surge tank for a blockage. Its the "bolt with a hole in it". If his tube gets clogged, it will allow an air pocket to form around the water pump impeller and it will stop coolant flow. Sometimes gasket material or a clump of stop leak material willl plug up the hole.