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I have a new thermostat, coolant, water pump, and radiator. The temperature gauge in the car never gets above the halfway mark, fans turn on with the A/C, and the heater is hot. After I fixed a leak on the hose (I put a clamp on the hose connected to the thermostat) I got to thinking. I did a search here and found to see if the hoses were hot after running the car. After driving around for 20-25 minutes, I checked the radiator hoses. The top hose is hot but the bottom hose, the one connected to the thermostat, is cold. Does this mean the thermostat is closed? Wouldn't my car overheat? I don't want to waste my time checking for a faulty thermostat or taking it back to the mechanic stating he didn't do the work I paid for. I'll gladly take it back to him since I've already paid for it. Do you think it is shut, backwards, faulty, or is this normal? FYI-It's a brand new toyota thermostat that's only 3 months old. Thanks for any input.
I think this happened to me when i changed a t-stat on a minivan we had, the lower hose was cool most of the time but it went away after a day or two of driving, probably air bubbles.
i don't think there's anything wrong with your thermostat....the lower hose is supposed to be cooler than the top.
the top is the coolant running into the radiator to be cooled, the bottom is the result of cooling and should be cooler than the top.
Unles your temp gauge fluctuates, i don't think you need to worry at all since everything is new. plus when thermostats fail, they fail in the open position..
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RningOnFumes, i have to disagree about thermostat failures...4 yrs ago, on my 85 Nissan 200sx the thermostat stuck shut causing the the temp gauge to quickly go all the way to the right to full hot. Fool that i was, i did not believe my gauge and kept driving. That $5 thermostat cost me $1200. For a used japanese engine to replace the one that burned the piston, all because of a stuck thermostat.
theres a "TRICK" to find out if ur thermostat is opening and closing but dont remember if this is how it went. maybe sum1 else can help me out.
your suppose to take your radiator cap off and then start your car.
let it reach operating temp. and i think your suppose to watch the coolant swirl or its suppose to drop, not sure which is suppose to happen .
if it drops, that mean the thermostat is operating correctly.
I WAS JUST LOOKING THE THE "HAYNES MANUAL" AND IT SAYS IN SECTION 3-3
" IF THE ENGINE IS RUNNING HOT,USE UR HAND TO CHECK THE TEMP OF THE LOWER RADIATOR HOSE. IF THE HOSE IS NOT HOT, BUT THE ENGINE IS,THE THERMOSTATE IS PROBABLY STUCK IN THE CLOSED POSITION, PREVENTING THE COOLANT INSIDE THE ENGINE FROM ESCAPING TO THE RADIATOR.REPLACE THE THERMOSTATE."
my guess is that maybe your thermostate is installed wrong. but if its installed backwards then you would have an overheating problem. so i dont know.
Ok i had a t-stat problem just recently , so i should be able to give a few tips. First, you can check it yourself by doing one of 2 things, one warm your car up, with the raditor top off and watch the coolant, if it drops your t-stat is fine, second is to remove it completely from the car, easy to do :P but you'll need new coolant, pull out the t-stat and put it in a saucepan with water and boil the water, if it works it will pop open at around 80C i beleive .
My advice tho, is i doubt your gauge is wrong, but (if in doubt - check it out)
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1989 Camry SV22 (RIP) Blown Motor
Thermostats fail in the close position hence overheating ensues.
They can also fail in the open position resulting in long warmup times and the engine never reaching operating temperature. This results in wasted fuel and can eventually ruin your cat converter, since the engine is running such a rich mixture. The engine can not properly burn all the fuel that is sent into the cylinders and some unburned fuel is expelled out the exhaust valves and through the exhaust system.
If it fails in the closed position the car will overheat as someone already mentioned. When a thermostat fails in the closed position and you continue to drive, it can result in a ruined engine, as also mentioned above.
Neither of these 2 scenarios is advisable, as it it cheap and easy to replace the thermostat.
They are not designed to fail, but they can fail in either the open or closed position. It is, however, better that if it's going to fail, that it fails in the open position.
If your thermostat was stuck closed, you'd have no doubt. Your temp gauge would go all the way up and stay there and if you didnt shut the engine off you'd blow it up.
This happened to me on my nissan 200SX, i chose not to believe my temp gauge and paid the price. $1000 for new engine actually, it overheated and broke a piston.
OK, this is something that I would do. It's kind of stupid but I think that it would give you an indication that both your thermostat and your temperature gauge are working.
Drive around and let your car warm up. Note where your temperature gauge is at (a piece of tape might work). Secure a piece of cardboard in front of the radiator and drive around some more. If the gauge doesn't rise in a few minutes I would suspect your gauge is broken (your t-stat could be working or not. you wouldn't know). On the other hand, if the temperature goes up (as I suspect) you would know that the temp gauge is working. Quickly get out and remove the cardboard and drive around some more. The temperature should go back down to normal (where the tape is) in a couple of minutes or less. If it does go back down I believe that this would exonerate your t-stat. If not then be very suspicious of your thermostat. Obviously, don't allow your engine to overheat while doing this.
A more elegant way to do this would be to install a separate, temporary temperature gauge (or go to a mechanic) and monitor the temperature fluctuation. But then, where's the fun in that?
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, so i should be able to give a few tips. First, you can check it yourself by doing one of 2 things, one warm your car up, with the raditor top off and watch the coolant, if it drops your t-stat is fine, second is to remove it completely from the car, easy to do :P but you'll need new coolant, pull out the t-stat and put it in a saucepan with water and boil the water, if it works it will pop open at around 80C i beleive 
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