Thermostat. - Toyota Nation Forum : Toyota Car and Truck Forums

tnmk · 09-30-2006, 12:25 PM

I just bought the car a couple of months ago and thought it was running a little on the cool side, so I got a new stat, fails open for safety.

And now last night it was running barely above the C mark. It was fully warmed up prior to that. Could the new stat have gone bad already, or could it be the sending unit?

I'll take it apart tomorrow to see if it's failed open I guess.

diver9000 · 09-30-2006, 03:14 PM

Check and make sure your coolant is flowing.
Check and make sure your water pump is not leaking.
Check and make sure your radiator is not leaking.
Check and make sure your heater hoses are not crossed leading into the heater core.
Check and make sure your heater core is not leaking.
Check and make sure the butterfly (on firewall) opens and closes properly.

tnmk · 10-01-2006, 04:25 PM

So how do I check to make sure the coolant is flowing? And if it wasn't, wouldn't it be over heating instead of not heating up?

Also how do I check to see if the butterfly valve is working? It must be because I do have heat and I am able to turn it off.

Hoses can't be crossed because this happened suddenly. The only thing I've done to this car on the cooling sys is change the stat and all was fine for a good 1 1/2 months or so.

No leaks that I can see or smell.

diver9000 · 10-01-2006, 04:57 PM

You have 2 sending units that you should check. One is at the radiator and it basically tells the thermostat when to open and when to close.
You have one on the block that tells the water temp in the engine. I would check both of them.
You could have a bad thermostat that is stuck open and I have seen it happen, but not usually on toyotas.

freakinbox · 10-01-2006, 05:24 PM

umm not sure on the year of it. BUt on my ae92 the temp sending unit is in the thermostat housing. Check that

punter · 10-01-2006, 05:46 PM

Quote:

Originally Posted by diver9000

You have 2 sending units that you should check. One is at the radiator and it basically tells the thermostat when to open and when to close.

What? The thermostat opens and closes buy its self, the thermo switch your thinking of controls the fan.

I would double check that you have the correct thermostat, and that it isn't jammed, if that's fine then its a temp gauge/sender problem.

freakinbox · 10-01-2006, 05:57 PM

well it sounds like a temp gauge sender. Since even with the thermostat open it would eventually gain some heat.

diver9000 · 10-01-2006, 07:36 PM

Quote:

Originally Posted by freakinbox

well it sounds like a temp gauge sender. Since even with the thermostat open it would eventually gain some heat.

I agree with freak on this

Hey Punter, yes it does control the fan, but when the thermostat opens up the fan engages too to help cool it off. Without going into too much detail for tnmk I was just trying to give an easy way to look for a couple possible choices to check.. thats all

tnmk · 10-01-2006, 07:56 PM

Well I took out the stat to see if it was failed open and it isn't. Put it all back together, filled it back up with antifreeze, drove it and guess what! All seems to be back to normal.

So I would guess the temp sending unit is either going bad or I have a loose connection somewhere.

Thanks for all the input.

Bitter · 10-01-2006, 07:59 PM

could have been an air pocket in a bad spot.

tnmk · 10-01-2006, 08:04 PM

I suppose that would make sense, but after over a month ago that I changed the stat? Fluid wasn't low at all.

Bitter · 10-01-2006, 11:21 PM

i've seen some cars have air pockets causing some weird stuff for months on end! only overheats at idle but cools off when you rev it, hot air turns to cold when i stop, overheats at a certain rpm, temp guage goes all the way to cold during a hard stop, ect.

diver9000 · 10-03-2006, 06:44 PM

Toyotas are usually pretty good about leveling out the temp and any air bubbles in the radiator most of the time. Hmmm

Hope it doesnt happen again, especially with winter not too far down the road.