Watching your temperature gauge climb on the 118 in 100°F heat is terrifying. Here's what's happening, what to do right now, and how to prevent it next time.
You're driving home, the temperature gauge starts climbing past the middle, and suddenly you can smell coolant. By the time you pull over, steam might be rolling out from under the hood. If you've experienced this in Simi Valley summer, you know the panic is real.
Overheating is one of the few car problems that can destroy an engine in minutes. Continuing to drive an overheating vehicle can warp cylinder heads, blow head gaskets, or seize the engine entirely, turning a $300 repair into a $5,000+ disaster.
Here's what causes overheating, what to do immediately if it happens, and how to prevent it.
What to Do Right Now If Your Car Is Overheating
- Turn off the AC immediately. The AC compressor adds significant load and heat to the engine. Roll down windows for cooling.
- Turn the heater on full blast. Counter-intuitive, but the heater core acts as a secondary radiator and pulls heat out of the engine. You'll be uncomfortable, but the engine will cool.
- Pull over as soon as it's safe. Don't push to "just make it home", every additional mile increases the risk of severe engine damage.
- Turn off the engine and let it cool for at least 30 minutes before doing anything else. Do not open the radiator cap when the engine is hot, pressurized coolant can erupt and cause serious burns.
- Check the coolant level only after the engine is cool. If the reservoir is empty, the radiator may need to be topped off too.
If overheating happens repeatedly or coolant is visibly leaking, get the car towed rather than driving it.
The 7 Most Common Causes of Overheating
1. Low Coolant Level
The simplest cause and the one to check first. Coolant levels drop because of evaporation, small leaks, or normal use over time. If your reservoir is below the minimum line, top it off with the correct coolant type for your vehicle (check the owner's manual, using the wrong type can cause major problems).
If the level keeps dropping after you top off, you have a leak somewhere that needs to be tracked down.
2. Failed Thermostat
The thermostat is a temperature-controlled valve that regulates coolant flow. When it fails stuck-closed, coolant can't circulate to the radiator and the engine overheats fast, usually within minutes of starting.
Symptoms: Temperature climbs steadily even at low speeds, often without warning. Replacement is $150-$350 depending on the vehicle.
3. Failing Water Pump
The water pump moves coolant through the engine. When it fails, usually due to a worn impeller or failed seals, coolant doesn't circulate properly and the engine overheats.
Symptoms: Coolant leak from the front of the engine, sometimes a high-pitched whine or grinding noise from the pump area. Replacement is $400-$900, usually combined with timing belt service if the pump is driven by the timing belt.
4. Radiator Issues
Radiators can develop leaks (often around plastic end tanks on modern radiators), become clogged internally with debris, or get blocked externally by bugs and road grime.
Symptoms: Visible coolant leak underneath the front of the car, white or pink residue on the radiator, or overheating only at low speeds (when airflow through the radiator is minimal). Replacement is $400-$1,000+ depending on the vehicle.
5. Failed Cooling Fan
Most modern cars use electric cooling fans that turn on when the radiator gets hot. If the fan motor fails or the relay/temperature sensor that triggers it fails, you'll overheat at low speeds (highway driving may be okay because air rushes through naturally).
Symptoms: Overheats in stop-and-go traffic or at idle, but cools when you get up to highway speed. Repair is $200-$500 depending on the cause.
6. Blown Head Gasket
The most expensive cause. A blown head gasket allows coolant to leak into the cylinders or combustion gases to leak into the cooling system. Either way, the cooling system loses its ability to regulate temperature properly.
Symptoms: White exhaust smoke that doesn't dissipate, mysteriously disappearing coolant, oil that looks milky/coffee-colored on the dipstick, or an engine that overheats and pressurizes the cooling system after just a few minutes of running. Repair is $1,500-$3,500+, and many older vehicles aren't worth the cost.
7. Coolant Leak (Hoses, Fittings)
Rubber coolant hoses age and develop leaks, particularly common in Simi Valley heat. So do various fittings and clamps throughout the system. A small leak you can ignore for weeks can suddenly become a big leak that empties your cooling system in minutes.
What to look for: Greenish, orange, or pink fluid on the ground under the front of your car. Coolant smells sweet (don't taste it, it's toxic). Hoses should be firm but flexible, never rock-hard, soft, or bulging.
Repair: Hose replacement is typically $120-$300 per hose installed.
How to Prevent Overheating
- Get a coolant flush every 30,000-60,000 miles. Old coolant loses its corrosion inhibitors and heat-transfer properties.
- Inspect hoses with each oil change. Look for cracks, soft spots, or bulges.
- Check the coolant level monthly. Catch slow leaks before they become big ones.
- Have your cooling fan tested annually, particularly important before summer.
- Keep the radiator clean externally. Bugs and debris on the front of the radiator block airflow.
- Replace the thermostat at major cooling system services, they're cheap and a failed one can total your engine.
Diagnostic Pressure Test
If your car has been overheating intermittently or losing coolant mysteriously, a cooling system pressure test is a relatively cheap way to find the leak. The system is pressurized with a hand pump and watched for pressure drops, leaks become visible quickly. We charge $75-$125 for a comprehensive cooling system pressure test, which often saves hundreds in unnecessary parts replacement.
Get It Diagnosed at Perry's
Cooling system repairs are one of our specialties, between Simi Valley summers and the climb on the 118, we see everything. Our ASE Certified technicians can diagnose your overheating issue accurately, give you a written estimate, and back the repair with our 2-Year/24,000-Mile warranty.
Learn more about our cooling system service or schedule an appointment. Call (805) 522-5769, we can usually get overheating cars in same-day or next-day.
Need a trusted mechanic in Simi Valley?
Perry's Quality Auto Repair has been serving Simi Valley families since 2000. ASE Certified technicians. 2-Year/24,000-Mile warranty. Up-front pricing.