anyone have or heard of a overheating suby which has the following symptoms?.....
-overheats under severe load after at least 60 mins highway driving
-shifting down prevents overheating for at least another 10 mins
-replaced thermostat
-checked rad flow
-had three separate blocks tests passed all three, no sign of combustion in coolant at idle
-fans work to spec
-can drive around town no problem
-theres no coolant being burned, no white exhaust
-heater core gurgles
possible explanations, head gasket leaks when engine is hot, rad loosing capacity to cool, any others? anything for sure. changing head gaskets is $
1200

 

Your biggest hint to your problem lies in the "gurgling" heater core. That is air pockets. This is caused one of 2 things, either you haven't been able to completely bleed the system properly or your headgasket is leaking/burning small amounts of coolant.

First off get your cooling system bleed out completely. Then retest for your overheating problem.
Hopefully this is your problem...

but...it is mostlikely the one your fearing.

PS.... A leak down test would find out if you have a head gasket leak, this is the proper test for a complete head gasket analysis.

Nick