Not passing smog test

Ok, this is a good one.. It started with taking the truck to get a smog done on it. The mechanic called and told me i did not pass. He said that truck was not getting hot enough around the intake manifold. He told me that it needed a thermostat, i said ok replace it. Calls me back and said he replaced the thermostat and it is still is not hot enough to pass the smog test..So i go down and had him SHOW me what was going on with it. He left the original thermostat out and showed me the truck ran cool. He put a new thermostat back in it and ran it again, got hot only on the upper hose/side of the radiator Once again it was cold on the lower radiator hose up to the thermostat housing. When we shut the truck off the upper hose was boiling away. So he now says its the water pump, he would replace it for $550.00, i said "no thanks" So now i have a truck that overheats and wont pass smog. I have always worked on my own cars, my father had a full blown machine shop and automotive repair shop, at the age of 9 i was cleaning the carbon off valves and scraping head gaskets off engine blocks, so i know my way around engines. I bought this truck new in 98. I did all my own oil changes and tune ups on it It sat most of the time in the garage while i took BART to work daily. The truck has always been solid as a rock. Truck has 140.000 on it. I never changed the Toyota red coolant in it. So when i got it home i did the following things to it.
Pulled off both radiator hoses and put the garden hose in the radiator and checked for flow.it was fine!!. looked through the radiator cap hole it looked brand new, same with the lower hose hole.
Hoses are in great shape, watched to see if they collapsed while running, they did not. So i was just shaking my head and pulled the water pump off and it looked like it did the day it came off of the assembly line. Got the garden hose out and stuck it in the engine cavity, it had major water flo both ways. Pump looked good, replace it anyways. Put it all back together and it still overheated..Pulled out the thermostat again, ran it, ran fine no overheat. So this is the 4th thermostat that has been put in it along the way. I am out of things to do. Did i get four bad thermostats. Everything goes back to the Thermostat's. Not a head gasket, checked for that.What missing?

 

Air pocket on back side of thermostat? Try burping the coolant one more time squeezing the hoses. Lisle make a great funnel/bleeder available at most parts stores or tool trucks. Or possible your temp sender is bad.... I wouldn’t think it would be able to get up to temp with the thermostat out.

 

Yeah, maybe an air pocket, but filling the radiator to the top should get coolant above the level of the water pump and the water pump still circulates coolant past the thermostat when it is closed. Did you put in Toyota thermostats? The thermostat should have a jiggle valve to allow some air to escape past the thermostat even when closed. I've never experienced these problems the times I refilled my 2.4L coolant. The repair manual doesn't give any special instructions to fill the system. The air should work it's way out on its own, but maybe revving the engine a bit would help circulate coolant as it's warming up.

 

It started out not passing a smog test. well it finally passed the smog test. As you know i went through everything but a new radiator. That was the problem. Even when i took the house water hose and put it through the radiator and it flowed just fine. Put a new radiator it and drove it around the block, no overheating issues at all. I still cant believe it would not pass a smog test with a plugged radiator. Thanks for the help..

 

I don’t understand how that would cause you not to fail smog. What does your smog paperwork say? It should mention why it failed. Like bad EGR system, high hydrocarbons, NOx, etc etc.

 

the only thing I can think of is that the PCM never enters closed loop due to insufficient coolant temp and as stated above, the paperwork should have said exactly that.

 

This issue started years ago. The mechinic said it did not get warm enough and i needed to change the water pump so it would get the temp up. He did not know the radiator was the problem. i did not get any paperwork on it, my bad. So, im up and running. and thanks for hanging in there to try. and get this thing fiquered out.