Thermostat just won't open

Hello!
I'm new here but I've lurked around looking for answers and this seems to be a real head scratcher.

I have a 1999 Tacoma, V6,5spd, with 4wd. No mods (and I ripped out the dealer installed alarm). I just bought the truck off my boss recently.

I'll cut to the chase here... My thermostat won't open!

• I've tried 2 different brand new thermostats, one of them is OEM Toyota. Both failed to open.
• Both opened in hot water on a stove so they seem good to me.
• When I put them in the truck, the engine gets hot, but the coolant doesn't flow. Lower radiator hose is still cold as the air outside!
• I don't know what it could possibly be, all i can think of is that the hot water isn't reaching the back of the thermostat?

more troubleshooting info:

• When I got the truck it only got hot on the freeway. Upon further investigation, this is probably because the thermostat had 3 holes drilled in it by whatever shop it was last at (huh lol)
• With the hole-y thermostat, the truck would get hot on the freeway unless you turned the heater knob all the way hot. It didn't matter if there was airflow over the heater core. This leads me to believe hot water isn't getting to the thermostat for it to open??????
• I've run water through the radiator and block separately, both flow nicely, leading me to believe that there aren't any blockages
• The radiator was replaced in 2014, along with the water pump, timing belt, and ALL the hoses, both head gaskets, and a head (that was an expensive one they left the bill in the glove box)
• I've done a exhaust gas in coolant test, no head gasket leaks
• The truck runs fine (but cold) with no thermostat installed, leading me to believe it's the thermostat

I thank you all for your time in advance!

 

Sounds like you have a blockage somewhere, but it's confusing that the water runs through fine (but separately).

Have you ever used HeadGasket Fix / Stop Leak that goes into the radiator?

That stuff ruined my radiator and almost clogged up my heater core.

 

I sure haven't, but I can't speak to the previous owners' actions.

 

Sounds like you it is air locking when you assemble it. Probably the reason it had holes drilled in the thermostat when you removed it. That is a common way to relieve the air pocket that forms at your thermostat when you first fill it up with coolant. Some thermostats actually come with a small hole in it for that reason. Maybe the water pump itself. You can run it without a thermostat and look in the radiator and see if you see coolant flow. I had a CJ7 that I searched and searched for the reason it was running hot only to fine the impeller on the water pump had turned loose from the shaft, hence no water flow.

 

There's coolant flow with the thermostat removed.
I've tried burping (I think that's what it's called?) the system by parking on the local hill and squeezing hoses, no real change.
Any other tips how to get water out of the system?

 

I have always drilled a very small hole say 1/16" or so, then no burping required. But it seems like you are air locking it and the burping procedure you are reading about does not always work. How hot does your gauge show, or does it show anything at all

 

Is the engine overheating? What does an OBD2 scanner report the coolant temperature?

The bottom radiator hose is supposed to be cold! The radiator cools the coolant before it gets to the bottom hose.

 

A defective temp gauge sensor or the dummy gauge is not functioning properly? Hook up a live data scanner and see the actual temp, that will help.

 

temp gauge on the dash reads just under the red.
OBD2 scanner read up to 230 before I shut it off because I don't want a sad lump of aluminum on top of my block.

Yeah i understand it should be cool, but by cold I mean the same temperature as the air, not even slightly warmer. No warm air is coming off the radiator either, so I don't think it's supposed o be *that* cold.

 

this is rather odd. You are going to have to check everything, again. I would take the radiator out and with the cap on put on the ground and with a garden hose and a rag to seal the lower outlet turn the hose on and see what happens. It should flow pretty freely.

There is a fan shroud and the fluid coupling is good? A good fluid coupler will make lots of noise on a cold start and within a minute or 2 slow down.

The AC condensor isnt blocking air flow to the radiator is it?

the jiggle valve on the thermostat on the 3.4 goes at the 6 oclock position.

you can verify water pump operation by taking the outlet line off of the heater core and reving the motor. If the heater core isnt plugged it should squirt pretty good.

 

Fan shroud and fluid coupling are good. It wants to be an airplane on startup but relaxes after a couple seconds.
AC condenser is pretty clear, no bent fins either.
I'' double check the thermostat, but i think i put it there.
I will DEFINITLY check the water pump and report back later today, and same with the radiator.

thank you all for your responses and time, i really like the truck, but this issue needs to go :/

EDIT1: water pump works, glad i wore glasses for that one

EDIT2: radiator flows well, thermostat jiggle valve was in the 7 o clock position, so pretty close... !@#$%*&

 

update for those still following:
when i pump water into the upper radiator hose it comes down where those blueish purple lines are, around that back piece.

When i try pumping water into the hole circled in red, it doesn't seem to go anywhere. (heater on full)
AS FAR AS I KNOW, that's the coolant line that runs in a circle in the block, so that might be blocked, or i might be tripin'.
This is according to https://www.tacomaworld.com/threads/5vz-fe-cooling-system-question.397808/ images from this thread

 

UPDATE part 999:
diagram showing where water does and does not flow (i think?)

 

Thermostats installed backwards.

 

Since this seems to have been a problem before hence the extra holes.

You don`t mention lots of brown discolored coolant at the flushes.

Both thermostats got dipped in the boiling water and passed.

Just a thought !!

A aftermarket water pump that was machined out of round just enough when the thermostat is tightened down it is enough to cause the thermostat to bind and not open after all your not dealing with all that much pressure.

Best of Luck.

 

I'm not familiar with the 1st gen thermostat. Is it possible it was installed backwards?

 

I don't know. But if water moves with it out, and it's been verified as being good, the only solution is something physically preventing it from opening. 99.999999999% of the time that happens, its installed wrong.

 

burp the system up on the firewall, where the heater hoses are the highest point.

 

It looks like by your diagram above, that your flow is opposite?
The top hose shows flow OUT, but you have it as Flowing IN?

 

sorry for super late reply, semester woes.
I was testing coolant flow with an external pump for that diagram, the coolant usually flows out the top as it should.

Update to the situation: oil cooler is leaking oil, so i'll be replacing that. Perhaps it's clogged somehow? Unlikely but i gotta stop dumping oil on my boss's parking lot.