Thermostat adjustment boiling the water out of the reservoir

Vehicle make YEAR and model?

Of the water is boiling them it has run hot. There is no way around this fact. Get a compression test done first. This should reveal if any damage has been done. Then address the boiling off problem. This can be a air pocket in the line, incorrect anti freeze mixture, sticking thermostat, water pump, cap, etc.

Pam are you sure it's boiling? If the Antifreeze is boiling I'd think you'd see steam coming out of your reservoir as the water expands into the reservoir, but you didn't say you see anything like that.
Of course engines get hot, that's why we have the cooling systems but it doesn't sound like it's "boiling" to me with no signs of visible steam unless your antifreeze level is really low?

If it's really boiling, and you antifreeze level is good, then your reservoir should be getting filled up with expanded hot water that goes into it to catch it when it expands.

If the water isn't going into the reservoir, then maybe your antifreeze level in the radiator is too low and you need to add antifreeze?
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Best to fill the radiator with the engine cooled down. If you ever have to open the radiator when it's hot, NEVER open it with your bare hand as you could get scolded with boiling water. Instead use a big thick towel to remove the radiator cap off a hot engine. Again, if you can, just wait until the engine cools then open the radiator cap.

With the engine cool, you can fill the radiator with a 50/50 antifreeze mix. The 50/50 mix come premixed 50 percent water, and 50 percent antifreeze. So you can throw that stuff straight into the radiator.

Non mixed antifreeze needs to be mixed 50/50. Some people use 50 percent distilled water when they mix it because distilled water doesn't have the minerals in it that may get stuck in your radiator. That's being a bit picky about it though. Tap water works fine in a pinch. The other 50 percent is antifreeze. You can mix it right in the radiator too, put in a measured amount of the antifreeze, followed by the same measured amount of water. The water pump will mix it all together when you run the engine.

Put the cap back on and run the engine and if/when the water "boils" it should go into your reservoir. If it does boil in go in the reservoir then yes...your engine is getting hot and the antifreeze is boiling.

When the antifreeze boils, it's probably because your thermostat is stuck closed. That means the thermostat isn't letting water circulate through the radiator to get cooled. Thermostats are cheap...no more than $30 I'd say for most cars. Changing them is pretty easy too as they are usually right at the top of the engine. A mechanic may charge $100 to change it....but it's an easy job on most vehicles requiring just a couple sockets/socket wrench.

Considering that the vehicle was never intended to reach the extremely high mileage it has, it is possible that pressure loss from the one of the cylinder chambers is occurring and leaking into a coolant channel, causing air bubbles to surface at the coolant reservoir. In this case, it may be a bad head gasket or a cracked head. Have you noticed a significant decrease in engine power of late? Is there any oil sheen appearing at the top of the coolant in the reservoir?

check your engine oil for water and water for oil your head gasket may have blown. failing that the water pump has gone and not pumping the water round. with engine running you should feel the water round if you squeeze the pipe near to the thermostat.

Remove the thermostat and drive car without it. See what happens. If that doesn't work take car to a reliable mechanic. Good luck .

thermostat?

check the water pump and make sure the thermostat is installed spring towards the motor, park it on a uphill incline, and run it at idle until the thermostat opens, you may have air in the system from it boiling over,, doing this will in effect Burp it, be sure and leave the cap off, and when the thermostat opens look in the radiator to see if the fluid is flowing properly,, use the correct anti freeze mix

sounds like a blockage like a dodgy thermostat, id test it by boiling a jug and throwing your new thermostat in the boiling water and see if it opens, other than that you've pretty much done it all so id be looking at a blown head gasket. good luck :)

check the thermostat good luck