Hi,
I have a -85 z with 880 block(vortec),EQ vortec heads and stealthram intake.Radiator is Modine replacement,and thermostat is 180F and there is original air dam.Problem is that temperature raises suddenly from normal(180F) to 240F.This happens in few seconds.Last time was at light cruise ~40mph.Temperature raise is real,because when I touch upper radiatorhose when gauge shows that 240F, it feels like boiling inside hose.I have drilled four 5/32" holes to thermostat body.I have read that there is some differences at cooling passage between pre-96 blocks and vortec blocks(96-00),should I make other modifications than that holedrilling to thermostat?.Is there air in the cooling system or what can cause this??

-Jari-

 

I'm pretty sure that there is air in the coolingsystem,because when temperature raises upper radiatorhose isn't "hard".Does heaterhose routing matter anything with this problem?Heater supplyhose goes from waterpump to heater and return hose goes to radiator.Why this engine doesn't remove air away itself as my previous 305 tpi does???
ANY IDEAS!!!
edit:I drilled bigger 3/16" holes to thermostat->no difference...

 

Water pump setup for the wrong direction of rotation?

 

I use same waterpump(and other assessories) that was at 305tpi(-85).Pump has been "driven" about 30t miles, and it is standard rotation cast iron pump.Today when I looked tempgauge shows almost 260F and fan wasn't running.Tempgauge sender is in driverside block ,and fan temp sender is at intakemanifold.It takes about one minute when temp goes up and come back to normal.

-Jari-

 

I found propably cause of this mystery->heater core has a very small leak.Didn't leak any antifreese to carpet.Found that when installed new prom to ecm.Going to replase that core and see if that works.