Q&A for How to Tell if Your Car's Thermostat Is Stuck Closed

Replace the engine coolant temperature sensor. Periodically, sensors go out, and that one is common.

It sounds like the thermostat is stuck open.

Yes. Without a thermostat your engine won't get to the operating temperature the computer is looking for so it will think the engine is cold and enrich the fuel mixture to help warm the engine. That's like driving with the choke on all the time, the engine won't run right, you'll pollute the air, & your gas mileage will suck. Newer engines run hotter & that added heat helps burn the fuel more completely, reducing emissions. Most cars these days run a 195 degree t-stat & some engines run as hot as 220 -230 degrees. That's because every pound of pressure the cooling system builds increases the boiling temp of water by 3 degrees. A 15 psi system increases the boiling temp by 45 degrees to 257.

It can. But if your thermostat gets stuck at all, replace it. They're very inexpensive. With basic tools, you can easily replace it. It's better to spend $4-15 on a new one than to buy a new engine.

If your thermostat is closed, there is nowhere for your water to go but out the overflow.

Yes--you probably need a new water pump as it is the component that circulates the coolant through your engine.

If your blower fan only works on high, there are three basic possibilities. The switch could be bad, the fan motor could be bad, or the most likely is that the resistor that controls the fan speeds has gone bad. Typically these are not too expensive nor hard to replace. Some are mounted on the firewall inside the engine compartment, and some behind the dash, but almost always on the passenger side and close to the fan motor itself. Unplug it, remove two screws or nuts then just reverse the procedure once the new one is in place. Just make sure the ignition is off when you do it.

As with all engines, if you remove the thermostat, the coolant will not circulate through the engine evenly. Without a thermostat, much of the coolant entering the head will take the path of least resistance streight back to the radiator. You may not know that this is happerning depending on where the temperature sensor is located.

Poor mechanical timing could cause an engine to run hotter. However, this usually comes with other issues, such as a rough idle.

If it has an obdII port, some scanners can read it out from computer (cars from mid 90's and newer).

Two possibilities. Your radiator cap is bad or it's the wrong one. If the rubber gasket inside the cap is cracked or worn so flat that it won't seal, the cooling system won't build the correct pressure to keep your engine operating at its peak or it will leak. Most people don't know that engine temperature gauges don't work without coolant and will usually show normal even if there is no coolant in the system at all. Take the cap to places like Autozone, Advance Auto, or O'reilly Auto Parts and they can pressure test it and your cooling system and make sure your cap is the correct pressure for your vehicle. Once you have the right cap, make sure the cooling system is full and you're good to go.

As far as the thermostat is concerned, no. Most thermostat housings are two pieces, and the thermosat sits in the middle; they tend to leak if you don't put the gasket back on, so try doing a pressure test at your local auto repair place, and see if you can find where the drips originate.

When the engine is cold, check your antifreeze level in the radiator. If that's full, remove the hoses to your heater core -- using a garden hose, push water through one of the heater core ends and see what comes out the other end. Then check your fan belt for tightness and wear. Re-attach and go for a drive; if the problem persists then replace the radiator and/or water pump.

Check the radiator fan fuses, relays, and resistors and replace if needed. If that doesn't work, check for any broken or frayed wires before replacing the fans. If your fan is belt driven, replace the fan clutch, belt and water pump.

The thermostat is stuck open. You'll have to replace it. Your loss of mpg and insufficient heating causes more wear as the oil isn't heating properly.

The only way to know is to plug it in. They do it free at Advanced auto parts.

No there is not, though you can get a thermostat that has higher degrees on it.

A thermostat is an automatic device for regulating temperature (as by controlling the supply of gas or electricity to a heating apparatus).

As long as the gauge stays out of the red you can run your engine slightly over temp for short stretches (like 7 miles).

If your engine overheats at an idle, your fan clutch has failed, your cooling system has not properly been maintained, or there's a internal discrepancy wreaking havoc upon your cooling system's functionalities.

No, it will just get hotter and hotter until it overheats; at that point, it might damage the engine.

All cars must have a thermostat, located on the engine side of the large upper radiator hose.

3 things cause an engine to over heat. 1. Bad radiator and hoses; 2. Faulty thermostat; 3. Blown head gasket. Check your thermostat first before replacing anything else.

Your A/C "recirculate" setting could be at the "off" position. Try turning it on. When off, air from the outside gets inside, blowing out of the vents just below the windshield. Depending on the weather, it could appear like steam is blowing through it.

It is not clear if you are talking about the air conditioning or the heater beginning to blow cooler. The heat will start blowing cooler, as the loss of coolant can no longer circulate to the heater core.

Good chance it's a faulty sensor. Check with your car manufacturer for possible causes. If swapping out the sensor doesn't help, then a reputable mechanic will be the next option.