After a lot of reading and research here, I swapped out my 3VZE for a 5VZFE. Can't really complain about the 3VZE as it lasted 524K and still ran when I pulled it, cracked block and all.

5VZFE are very hard to find around here, so I picked up a junkyard 1995 model that was tenderly loved up until the T100 it was in was totalled sometime around 200k. It is in great shape with new factory timing belt, water pump, and pulleys. I put new valves in the head and checked the motor over.

I swapped the motor in and it all went as expected. With the exception of the thermostat. I can't get it to open. Using water (to flush everything out), and it will boil the water out before the thermostat opens. The top radiator hose is hot, and the bottom, ice cold.

Things I have tried.
I tested the thermostat by boiling it in a bucket of water, and it opens at the right temps.
I tried it jiggle valve up and down, and even removed the jiggle valve. No difference.

I put the front of the truck up on ramps about 1 foot off the ground, no change.
I squeezed hoses and blipped the throttle, no help.
No bubbles seen in the radiator next to the normal.
Heater gets hot.

I ran a garden hose in the radiator, good flow, no restriction.
I removed the thermostat and ran the hose into the top coolant line and watched water flow out the thermostat housing. Good flow.

I cut the back of the thermostat off so it's just a plate and gasket, aka run with an removed thermostat. With this, the engine never gets up to full operating temp, but it does not overheat and the radiator warms up evenly and upper and lower radiator hoses are warm/hot. I have been driving it around all week and no overheating.

Today I picked up a factory thermostat, installed it (jiggle up, might be wrong) and added coolant. Same problem, but do to the coolant, it didn't boil over. But it did get into the red with the bottom hose staying cool.

I am assuming if my radiator was blocked up, it would still overheat with the thermostat removed. But it does not and the 3VZE never had cooling problems.

Head gasket leaking also should cause a general overheating, not causing the hot and cold difference between the top and bottom of the radiator. It should also cause it to over heat even with the thermostat removed.

My last step is to rotate the thermostat so the jiggle is down, but next to that, I am out of ideas.

Thanks for any help.

 

Moved jiggle down. No help. Watched temps get to 240F before shutting it down.

 

Not to be smart you are installing the thermostat in the correct direction.

New Hoses I would venture ??

Bottom Hose not being sucked closed ??

I have never had a problem with the 3.4 needing burped like the 22Re engines

 

Next to rotation, I can't install the thermostat backwards.
New upper and lower hose.
No radiator hoses are getting sucked in.

 

Comes down to the Thermostat not opening

Water pump impeller worn to the point flow is not enough to cool things

Some thermostats you can get in back wards

 

Found the problem. I had swapped the left and right head gaskets. I didn't realize it was possible to swap them so I didn't pay attention when installing them.

 

Thank you for the heads up.

 

t stat goes in the 6 o'clock position on the 3.4. Fill the top radiator hose into the block first, then hook it up to the radiator and fill radiator. Do this with a heater hose disconnected from the heater valve so the air pushes out when filling. Use only toyota red .

 

Glad you figured it out.

What made you recheck the head gaskets ??