> **Quick Answer:** A thermostat stuck open usually causes slow warm-up and poor heat, not overheating. If your car is overheating with a stuck-open thermostat, you likely have a second problem: a failed water pump, a blocked radiator, or a coolant leak. Pull over now, shut the engine off, and call a tow. Driving an overheating engine for more than a few minutes risks a seized engine or a blown head gasket.
## Why Is My Car Overheating If the Thermostat Is Stuck Open?
A stuck-open thermostat lets coolant flow constantly through the radiator, which normally keeps temperatures too low, not too high. If your temperature gauge is climbing toward the red while your thermostat is stuck open, something else is also failing. The most common culprits are a blown head gasket pushing combustion gases into the cooling system, a failing water pump impeller that has lost its fins and can no longer circulate coolant, or a radiator clogged badly enough that constant flow still cannot shed heat. A stuck-open thermostat on its own is a comfort and fuel economy problem. Combined overheating is a stop-driving-now emergency.
Check your coolant reservoir. If it is empty or you can see bubbling in a cold overflow tank, that points directly toward a head gasket leak. White smoke from the exhaust seals the diagnosis.
## Should I Keep Driving or Pull Over Right Now?
Pull over. Shut the engine off. Do not keep driving an overheating car trying to reach a shop, even if you think you are close.
Modern aluminum cylinder heads warp at temperatures above roughly 220 to 230 degrees Fahrenheit, which happens fast once the gauge enters the red zone. A warped head or a blown head gasket turns a few-hundred-dollar thermostat and water pump job into a repair bill that can easily exceed the value of an older vehicle. The risk is not worth it. If your temperature gauge is in the red or your engine is steaming, you have already pushed it far enough. Turn off the AC, crack the windows, and if the gauge drops back into the normal range while idling, you may have a few minutes to coast to a safe pull-off. If it stays high or climbs, cut the engine immediately.
For more on the decision between driving and calling for help, see [Car Overheating: Towing Cost vs. Driving to the Mechanic](/car-overheating-towing-cost-vs-driving-to-mechanic-risk/).
## How Do I Stay Safe While I Wait for the Tow?
Get completely off the road, onto a shoulder or parking lot, before you stop. Do not open the radiator cap. Steam and coolant under pressure can cause serious burns.
Turn on your hazard lights the moment you decide to pull over. If you have reflective triangles or road flares, set them out at least 100 feet behind the vehicle. At night or on a high-speed road, stay out of the car if possible and get behind a guardrail or barrier. Call your tow first, then your insurance company or roadside assistance to verify coverage. If you broke down on a highway or freeway, staying inside the vehicle with your seatbelt on is sometimes safer than standing outside in traffic. Use your judgment based on shoulder width and traffic speed.
If you are on a highway at night, [Broken Down on Highway at Night](/broken-down-on-highway-at-night-safety-tips-what-to-do/) covers your safe
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ty options in detail.
## What Will the Tow and Repair Cost Me?
A local tow of under 10 miles typically runs $75 to $150. Longer highway tows run $3 to $7 per mile after the hookup fee. If you have AAA, most roadside assistance plans, or an insurance policy with towing coverage, that local tow may cost you nothing out of pocket.
The repair cost depends on what actually failed. A thermostat replacement alone is one of the cheapest jobs in auto repair, often $150 to $300 parts and labor. A water pump on most four-cylinder engines runs $300 to $600. A head gasket replacement is where costs get serious: $1,500 to $3,000 is common, and on some engines it goes higher. If you caught the overheating early and pulled over fast, odds are good you avoided head gasket damage. If the engine was steaming or you drove for several miles in the red, get a full cooling system diagnosis before authorizing any repair, because you want to know the full scope before committing money.
Check your towing coverage before you call a truck. USAA, GEICO, and State Farm all offer roadside towing add-ons that can offset the cost significantly. See [Does GEICO Cover Towing After Breakdown](/does-geico-cover-towing-after-breakdown/) for a quick breakdown of what those policies actually pay.
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## Common Questions
**Q: Can a thermostat stuck open actually cause overheating?**
A: On its own, no. A stuck-open thermostat causes slow warm-up and heater problems, not overheating. If your car is overheating with a stuck-open thermostat, a second failure is present, most often a water pump, head gasket, or severely clogged radiator.
**Q: How do I know if I blew a head gasket while overheating?**
A: Look for white sweet-smelling exhaust smoke, coolant disappearing without visible leaks, oil that looks milky or like chocolate milk on the dipstick, or bubbles in the coolant reservoir when the engine is cold. Any one of these is a strong indicator.
**Q: Is it safe to add water to an overheating engine to limp it to a shop?**
A: Only if the engine is completely cooled down, which takes 30 to 45 minutes after shutdown. Adding cold water to a hot engine can crack the block or head from thermal shock. If the car is truly overheating and you have no other option, wait until it is fully cool, add water or coolant, and drive only if the temperature holds normal. Otherwise, tow it.
**Q: Will my car start again after overheating?**
A: It might, but that does not mean it is safe to drive. If it cranked hard, has a rough idle, or the temperature rises quickly again, stop and tow it. [Car Won't Start After Overheating](/car-wont-start-after-overheating-do-i-need-tow/) covers the specific scenarios where a tow is required versus when you can try to drive.
**Q: How long does a thermostat replacement take at a shop?**
A: On most engines, 1 to 2 hours. It is a straightforward job. The shop will also pressure-test the cooling system and typically bleed the air out of the lines before returning the car. If they find a second problem like a water pump or head gasket, the estimate will change significantly.
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Car Thermostat Stuck Open Overheating: When You Need a Tow Right Now
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