Running hot except when the heater is on...

Just got my Tacoma back ('99 Sr5 4x4 3.4 V6) after a rebuild. All new water pumps, thermostat, etc... It is running hot except when the heat is on. I replaced the thermostat again (from toyota) and the same thing is happening. The directions said that the jiggle valve should be within 15 degrees of vertical (which it is). Should I put the jiggle valve at the bottom? I read another post on here where that fixed the problem.

 

Perhaps there's air in the cooling system.

 

Once is cool down . Open the cap and turn on the truck and look to see if the water is moving . I had the same problem and I put mine on the wrong way.

 

This may Not be Your problem; but I did see this situation on an older, 4 cyl car, a few years ago.

As it turns out the radiator was, partially clogged from the owner using stop leak (don't know the kind of stop leak) to try to fix a leak where a stone made a small hole.

The car never ran hot until a few bottles of the stop leak.

He could turn the heater control on to full heat, and the car ran fine. Keep in mind the heater core is probably as big as the radiator on that car. It was a plastic/aluminum radiator. WE got another radiator from a salvage yard; and it fix the heating up problem.

oldracer

 

He is right feel the temp on the hose all 4 of them and see if they are the same temp

 

Id say its probably the radiator. If it was disturbed by the rebuild with high milage it is probably bad now