rebuilt with cooling problems

[DW]

Overheating: Turned crank, bearings, pistons oversized w'rings, head done, water pump, rad, hoses, heater core 180 thermostat. Running at higher rpm motor really heats up..almost to red line..thermal switch is new...fan won;t come on all the time..temperature in rad near thermal switch not hot enough to make it run....any tips appreciated.DW

[jtanguay]

its your thermostat most likely, or you need to bleed the air out of the system by running it up to temperature with the expansion cap off.

i had the same issues when running this ridiculously hot thermostat. -20C weather outside on the highway doing 110km/h heater blowing on max, and engine temp still climbing... it was just a stupid amount of heat man... lol sauna in the dead of winter.  but i kept it on to ensure my HG didnt blow.  i thought of all kinds of things like water pump belt slipping... internal pulley detached and not spinning fully... you name it.  changed thermostat and voila... boy was i pissed off!!!  if untested i suggest you change it.  if its an mk2 and you run to the red... is there even a red?  red is like 120C isnt' it? if i'm not mistaken, that is like.. HG death zone...  all it would take is a nice steep hill climb with your foot into it to blow that sucker.

oh yea my rad would be bone cold while driving, and if i stopped the car and felt the rad it would get warm then hot, and the cars temp would even off.  idling the car would maintain proper temps.  its just that the thermostat wasnt open fully... it opened fully at around 105-110C  :shock:

[burn_your_money]

jtanguay sounds to be dead on

A garbage pump or loose belt slipping at high RPM are also suspect as well as collapsing rad hoses.