Thermostat not opening
 

Hi all,
Very recently my thermostat has stopped opening. Ive tried taking it out and boiling it and it opens and closes smoothly and at the correct temperatures. The Coolant hose coming off the T-stat is staying cold but the Temp at the coolant sensor has hit about 230F. Also i tried bleeding the system with the car on ramps and the T-stat opened fine but on the road it is refusing to open. Anyone have any advice?

How much did your thermostat open? I think they are suppose to open at least 1" or so.

Get another thermostat...

Just get another thermostat. They're cheap and if it is still overheating (and your're sucessfully bleeding it) then you can throw the possibility of it being that out the window. KAs are kinda hard to bleed if you're not sure how to. Just puttinn it up on the ramps isnt always gonna fully bleed the system.

I figured it out! Apparently my top radiator hose was a little loose and sucking in air/no holding pressure so every time i drove the car the system would fill up with air. I tightened everything down and bled it and it works like a champ again!

I'm having an issue with my cooling system also. The car would run hot if it sat idling for around 10 minutes or so, no problems while driving. I installed a new thermostat and now it does not overheat at all and the heat works great but the lower radiator hose stays cold and doesn't have much pressure and the top hose is hot and pressurized. Any ideas?

So its overheating at idle? Your new thermostat may be the wrong temperature range. Either that or your water pump isn't moving enough coolant at idle to heat up the thermostat.

First off, let me say sorry if I have thread jacked. Ok, now that that's out of the way. The car was overheating with the old 180 degree Altima thermostat. It does not overheat now with the new 170 degree thermostat. It idles and drives fine now with no over heating. The only puzzling thing now is the cold lower radiator hose. That is what has me confused.


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That's okay, my problem was resolved. If your lower hose is cold it means your thermostat isn't opening. Have you tried bleeding your coolant system?

Yeah, I have bled it with the bleeder screw and by raising the front of the car and burping out all of the air. I have had problems with it overheating before when I didn't have an overflow tank. If the new thermostat wasn't opening wouldn't it run too hot? If so, that's still the part that confuses me. Does the lower hose just stay cooler by nature?


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Well yeah, that's why its overheating. The lower radiator hose feeds colder coolant from radiator into the motor. If the hose is still cold then the t stat isn't opening.

I'm sorry, I must not have been clear. The car is currently NOT overheating with the new thermostat yet the lower hose is still staying noticeably cooler than the upper hose. That is what is confusing.


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Yes. I've been in the same position as you. Bled the system, no overheating, noticed the lower hose is pretty cool. I'm convinced at this point that it's normal and I just never noticed before.

Good enough for me. I just wanted to know if anyone else had experienced the same thing. Thank you.


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It could be colder because you have a colder T-stat so there's less heat soak. But yes that hose should be noticeably colder than the top hose.

The lower radiator hose is noticably colder because it's a gravity-feed system in addition to circulating via the water pump... Hot coolant comes into the radiator via the upper hose, gets cooled as it flows downward... By the time it reaches the bottom hose to go back into the engine; it is several degrees cooler.

Not sure why anyone would use an Altima thermo instead of an OEM 240 part in this case.

Yeah, as far as the Altima thermostat goes, that was a bonehead move on my part. My car was running cold (as far as the heat) last year and for some reason I listened to someone when they told me running a higher temprature thermostat it would help with the lack of heat. The Altima thermostat is 180 degrees and has the same physical dimensions. Anyways, you live and you learn. I think the problem is fixed, thank you everyone for the help.