[Supras] Overheating/bubbling from overflow tank

[Charismatisch at aol.com]

Hi guys and gals,
 
although the car runs fine in normal traffic, it still goes into the red  
zone after an Autobahn drive. When I get home, it spits water from the overflow  
tank onto the floor.
 
I have been given several reasons for this (BHG is repaired - only about  60  
miles travelled since done!).
 
1.) Rad. cap not working (don't think so).
 
2.) Air-bubble in water-system (possible).
 
3.) Timing not right (possible, as was set manually after  BHG-repair).
 
 
Who has had experience with one or more of these problems with the beast,  
and who can explain to me, why a bad timing can make the Supra overheat?  
(Doesn't seem to be the case with other cars).
 
Many thanks in advance,
Derek
88T Auto.