How do I check a car thermostat with boiling water?

Question

My car is overheating. I put in a new thermostat, test drove it - it overheated and the coolant backed up big time into the overflow tank. A guy said to pull the new thermostat, drop it in a pot of boiling water and "see if it opens." He said sometimes you get a new one and it's bad. So I did that. The copper button moved out some, but how do I tell if it "opened?" Should I be able to see light through it at some points?

The answers are good so far but my main question is: when I look at the thermostat after it has been in a pot of boiling water - what should it LOOK LIKE when it is OPEN? Thanks to everyone though, so far, for your help.

Answer 1

First off, if you drop the thermostat into boiling water that is at least 190 degrees, you should see the center disc move away from the outer disc.

On a more realistic note, I doubt you have a bad thermostat. What was your reason for replacement in the first place?

If the car wasn't overheating originally, more than likely you have an air pocket in the cooling system. Many cars come with a bleeder somewhere in the cooling system that allows air to escape. If you do not bleed the air out, you have a cavity with no coolant. This expands at a different rate than the coolant and can cause some serious issues with the vehicle. Please respond with more information about why you replaced the thermostat and what kind of car you have.

Answer 2

Lots of incorrect info out there. To answer your question, you need a thermometer or a way to measure water temp. Put the thermostat in a water filled pan and apply some heat. Once the water temp reaches 180 degrees, or whatever temperature is stamped into the thermostat, the center of the thermostat should move or open up. Not all thermostats open at 180, some open higher. You can run without a thermostat, but it I don't recommend it. I have known people who do it all the time without any trouble at all, but I won't. It's also very easy to put the thermostat in backward. That's not good either. Make sure it's in correctly and bleed the air out of the system.

Answer 3

No, no-leave the thermostat out, and put everything back to gather. Run the car for an hour or so. If it heats back up, then that was not the problem. Look at the water pump or radiator could be plugged. If it runs cold, then either the thermostat was bad or in backwards,

Answer 4

Did somebody replace the bottom radiator hose by any chance? People are always leaving the springs out of those things and they collapse from the water pump suction.
It's ok to leave thermostat out as a test, but Mazz is an idiot. Thermostats aren't there to cool the engine. They're there to keep the engine hot enough. It would run like crap and emissions would skyrocket if it was too cold.

Answer 5

Yes.

If you have an old car, like mine, and it is not an electronic thermostat (It's in line from the radiator into the intake manifold) you really don't need it.

Next, look at the structural integrity of your radiator. If it's corroded and alot of fins are gone, it isn't doing it's job and needs to be replaced.

Also do a bit of a tune up. Check and change the oil and tranny fluid. If they're low, they can cause overheating. Make sure you also have a good ground strap going from the metal of the radiator, from the attachment points, to the body of the car.

I live by the beach. About every 6-8 years, I have to replace my radiator from salt corrosion.

Answer 6

its also possible you have other troubles,,,check your radiator hose's,,if they feel soft and you can squeeze them together( then they are bad) when the water gets hot,the vac *** will cause the hose's to collapse and make the car over heat,,,,the radiator might be plugged up and need flushed out,,check the grill area of the radiator,,might also need to cleaned out(gets filled up with bugs over time),,make sure you have the correct amount of water-anti freeze,,,,and its also possible that the temperature sending unit could be bad giving a false reading of a high temperature,,,,as for your question on how to test a thermostat to find out if its good or not,,boil some water in a pan,drop the thermostat in and watch to see if it opens(would be a good idea to have a thermometer to see the temp of the water being boiled) good luck

Answer 7

do not run without a thermostat , you need the restriction to allow the heat transfer to take place , that's how heads and blocks get warped. try a rad flush , look at the rad for blocked tubes etc.hopefully it's just crud that the flush will get rid of, good luck.

Answer 8

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well a little bit more info would help pull your list of possibles down Is it over heating only when your going slow/stopped but when your going extremely fast (highway) your fine? that would be your fan hands down have you properly flushed your system out? that could do it too Check your radiator for any cloggs in your fins (visually looking at it) that could cause an overheat in no time could be that one of your hoses are weak and are collapsing upon itself when your coolant system is working correctly with the correct pressure headgasket could be leaking, check your oil for any water in it if you can oil cooler could be busted... transmission cooler could be busted... a clog inside your radiator could cause it too...

Answer 9

the reason it overheated and backed u pcoolant is because the system was air locked,you will need to bleed the air out of the system,some engines have a bleeder in the system up high or you can loosen a heater hose to let the air out,being careful not to burn yourself

Answer 10

possibly airlock in system, next time it starts boiling remove the radiator cap make sure you have a thick towel wrapped around your hand to avoid scalding. symptoms of head gasket failure are usually spots of water on dipstick. steaming exhaust, and when the water cools have a sniff in the radiator header tank if it smells sickly sweet it could well be head gasket. hope this helps. sean