OK, my friend has a 91 Accord and his car been overheating he recently replaced the thermostat, radiator cap, radiator and added new coolant. There's no signs of a blown head gasket or any coolant in the block and to top it off there's no leaks from any hoses or coming from the water pump. Fans do come on. The only things I can think of is the maybe the coolant sending unit is not working properly or at times or maybe even the timing might be off. Any input would be greatly appreciated.

 

did he "burp" the system correctly? made sure no trapped air pockets in the system?

did he put the thermostat backwards? or w/ the air/jiggle valve upside down, causing air pockets?

that's the only 2 things i can think of if you guys ruled out the other stuff u mentioned <shrugs>

ignition/emissions wise maybe something's causing a lean condition... running leaner will make it overheat; how's the egr valve?

 

Is the water pump good?