Hi gang, 87S4 just changed the side tanks. Got it buttoned back up & trying to top off fluid. When heater on full blast, the top of the radiator gets scalding hot. Even smoked a little. I turn the AC on for the fans and it cools down quickly. What gives?

 

Only the top? Any other hoses get hot too?

Do the fans NOT come on without the AC?

 

Both hoses are hot & fans did not come on

 

Without AC, fluid level in tank goes up. With AC on, it drops

 

You reconnected the radiator fan switch?

 

Ok, fans came on without the AC button pushed

 

Sounds like a air trap issue . try squeezing the top rad hose to work the bubbles out.

 

^^^^ This!

There's an air bubble in the water bridge that's keeping the hot water from opening the thermostat. Start with and maintain the reservoir FULL. Bleed the top of the radiator and the water bridge. Make sure the heater valve is open. Start the engine, and set the RPM's at ~~1500+ after a minute or two of initial warm-up/stabilization. It can also help some to set the car nose-down a little. Reving the engine causes the water pump to push the air through with the higher coolant velocity, so you can either rev the engine in the driveway or go drive the car some. Keep the reservoir FULL until you can feel the bottom hose hot, and/or the fans run without the AC switch.