over heating@idle

[ARTIC]

i have a 1986 6.2 GM diesel,i just replaced the thermostat,and the water pump a while back,when you shut it off,and its hot it slowly boils back in to the overflow tank,flow in rad is good,i checked when it was cold.not sure what to make of this,a head gasket or a rad flush,soon as you bring the rpm up to 1500 the temp is fine,and then ok for a while,10 min @ idle and shes over 200,just wondering whats up with that,thanks

 

[southernspeed]

This is going to sound weird but..... have you got a viscous (clutch) fan? We've seen a couple of oddball cases recently were the clutch fan was engaged all the time and at idle was was cooling the rad so much that it caused a vapour lock between the very hot engine and much cooler (relatively) rad.
Either way it sounds like a circulation problem. Hoses OK?

 

[four_by_ken]

Simple and easy thing that has to be asked first... have you checked the radiator for anything blocking it.... mud?

 

[84_Chevy_K10]

Fix your fan.

 

[four_by_ken]

Fix your fan.

You have such a way with words.