Why Is My Car Overheating?
- Tyler Ellis
- 3 days ago
- 5 min read
An overheating engine is one of those problems that can go from “hmm, that’s weird” to “tow truck time” in the span of a single commute.
If your temperature gauge is climbing, you see a coolant temp warning light, or you notice steam under the hood, your cooling system is telling you it can’t control engine heat the way it’s supposed to. That heat doesn’t just make you uncomfortable—it can warp engine parts, blow head gaskets, crack plastic cooling components, & turn a manageable repair into a major one.
If you’re wondering, Why Is My Car Overheating?, the answer usually lives in a short list of common failures. The trick is figuring out which one is happening on your vehicle before damage stacks up.
Why Is My Car Overheating? Common signs & what they point to
Overheating isn’t always dramatic steam & puddles. Sometimes it’s subtle at first.
Here are patterns that help narrow it down:
Overheats only at idle or in traffic: often radiator fan problems, blocked airflow, or low coolant.
Overheats mostly on the highway: often coolant flow problems (thermostat, water pump, restriction), low coolant, or internal engine issues.
Heater blows cold while the engine is hot: often low coolant or an air pocket (no hot coolant flowing through the heater core).
Coolant smell, wet spots, or low coolant reservoir: likely an external leak.
Temp spikes up & down: can be a sticking thermostat, air in the system, or intermittent coolant flow.
Those clues don’t replace testing, but they help us aim the flashlight in the right place.
What Causes This Problem?
Cooling systems are simple in concept: move coolant through the engine, dump heat through the radiator, keep pressure stable, & control airflow. Overheating happens when any one of those steps fails.
Low coolant (usually from a leak)
Low coolant is probably the #1 cause of overheating. Coolant doesn’t “evaporate away” in a healthy sealed system—if it’s low, it typically leaked or was pushed out due to overheating.
Common leak points:
Radiator end tanks & seams
Upper/lower radiator hoses
Heater hoses & quick-connect fittings
Water pump weep hole (small drip that gets worse)
Thermostat housing
Coolant reservoir cracks
Pressure cap that can’t hold pressure
Even a small leak can become a big issue because low coolant creates hot spots in the engine & reduces heat transfer.
Thermostat stuck closed or partially stuck
The thermostat regulates coolant flow. If it doesn’t open when the engine warms up, coolant can’t circulate properly, & temps climb fast.
A thermostat issue often shows up as:
Temperature rising relatively quickly after startup
Heater output that’s inconsistent
Overheating that comes & goes (sticking behavior)
Radiator fan not working (or not working at the right speed)
At highway speeds, airflow through the radiator is strong. At idle, the fan does the heavy lifting. If the fan motor, relay, fuse, or fan control module fails, you’ll often see overheating in traffic & “seems fine while driving.”
This can also happen if:
Fan is spinning but weak (worn motor)
Fan shroud is damaged or missing
Electrical connection is corroded
Water pump problems (coolant not circulating)
The water pump moves coolant through the engine & radiator. When it fails, coolant flow can drop or stop—especially under load.
Signs can include:
Overheating at higher RPM or highway driving
Coolant leak near the pump
Grinding noise (bearing failure)
Coolant circulation looks weak when tested
Clogged radiator or restricted coolant passages
Over time, old coolant, contamination, or internal corrosion can reduce flow through the radiator. Some modern radiators also clog internally in ways that don’t show obvious external signs.
A restriction can cause:
Overheating at speed
Temperature creeping upward under load
Uneven radiator temperature across the core (hot in one area, cooler in another)
Cooling system pressure problems (cap, reservoir, or air pockets)
Cooling systems run under pressure because pressure raises the boiling point of coolant. If the pressure cap can’t hold pressure, coolant can boil earlier, creating steam pockets that reduce cooling.
Air pockets can happen after a repair if the system wasn’t properly bled. Air doesn’t transfer heat like coolant, so temps can spike suddenly.
Head gasket or internal engine issue (less common, higher stakes)
If combustion gases leak into the cooling system, the system can pressurize, overheat, & push coolant out.
Possible clues:
Coolant loss with no visible external leak
Overheating that returns quickly after refilling
Bubbles in coolant reservoir
White smoke from exhaust (not always)
Milky oil (not always)
This isn’t the most common cause, but it’s one we take seriously because delaying can snowball damage.
How to Fix It?
There are two parts: what to do right now if it’s overheating, & what a proper repair path looks like.
What to do immediately if your car starts overheating
Turn off the A/CA/C adds heat load to the cooling system. Turning it off reduces stress.
Turn the heater on full hot & fan highIt sounds miserable, but the heater core acts like a small radiator & can pull heat out of the engine.
Pull over safely & shut the engine off if the temp keeps climbingIf the gauge is in the red or you see a warning message, continuing to drive can cause rapid damage.
Do NOT open the radiator cap while hotHot coolant under pressure can spray out violently. Let the engine cool fully first.
Check coolant level only after it coolsIf it’s low, topping off with the correct coolant mixture can help you limp to safety, but it doesn’t solve the leak or failure.
If the vehicle is overheating hard, the safest move is to stop & get it towed. A tow bill is cheaper than an engine.
What a proper shop diagnosis & repair usually includes
To answer Why Is My Car Overheating? correctly, we focus on proof-based testing instead of guessing.
Cooling system pressure test to find external leaks
Inspect hoses, radiator, pump area, thermostat housing, & reservoir
Verify fan operation (both speeds if applicable) & check relays/control signals
Check thermostat behavior (temperature rise patterns, hose temps, scan data)
Check coolant condition (contamination, wrong mixture, signs of neglect)
Flow checks when restriction is suspected
Block test / combustion gas test if internal leak is suspected
Once the cause is confirmed, repairs commonly look like:
Replace leaking hoses, fittings, radiator, reservoir, or pressure cap
Replace thermostat (often with housing, depending on design)
Replace radiator fan motor, relay, or fan control module
Replace water pump (often paired with belt service if applicable)
Cooling system service (flush) when coolant is degraded or contaminated
Deeper engine diagnostics if head gasket/internal issues are indicated
After repairs, we verify stable operating temperature in real conditions (idle, road test, load). That final verification is what keeps the problem from coming back next week.
Why Act Now
Overheating is one of the fastest ways to turn a normal vehicle into an expensive project.
Waiting can lead to:
Warped cylinder head or damaged head gasket
Cracked radiator or plastic housings from repeated pressure spikes
Coolant contamination (mixing types, adding stop-leak, or running low too long)
Breakdowns in unsafe spots (traffic, highways, heat)
Engine failure if it’s driven hot repeatedly
If you’re asking Why Is My Car Overheating?, it’s usually because the car already gave you the first warning. The smartest move is answering that warning while the fix is still straightforward.
Schedule Cooling System Service at Marble Falls Auto Center
If your temperature gauge is creeping up, your coolant level keeps dropping, or the car overheats in traffic, we’ll track down the cause & fix it the right way—so you’re not living in fear of the next red light.
Get scheduled here: https://www.marblefallsautocenter.com/contact-us
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