I have a 91 4wd pickup w/ 3.0 engine. I just replaced the water pump, thermostat and timing belt,all hoses and belts today due to the water pump being bad. After getting it all back together, running to operating temp and no leaks luckily I noticed that the bottom of the radiator is cold and the top of the radiator and top hose is hot. While the radiator was out I run water through it and it come out of the bottom as fast as I put it in the top. Any ideas? Thanks

 

ill bet its clogged.

undo the hoses leave the cap on, and then put a garden hose in the top hole. water should run out the bottom at the same speed its going in the top. (to a point).

just something to check.

 

May have not waited long enough for the radiator to get as warm as the engine, especially if it was cold out side. Thermostat only opens till the the coolant drops just under the opening threshold. So if the rad had cold coolant the thermostat wouldn't stay open long. So a shot of hot coolant rushes into the rad thermostat closes, heat rises. And boom your rad now has two temperature "zones" until more hot coolant rushes in. Take it for a spin, watch the temp gauge you should be fine.

I've got an aftermarket temp gauge and can tell right when the thermostat opens, when its cold outside the temp instantly drops after it opens.

 

Are you sure you got all the air bubbles out of the system??

Did you burp the system?