Why Your Car Overheats in Summer & What to Do | London ON
The temperature gauge is climbing. The needle is past the halfway mark and heading toward the red. There might be a sweet smell coming through the vents or a faint wisp of steam from under the hood. Your engine is overheating — and in London, Ontario’s summer heat, it is one of the most common reasons drivers end up stranded on the side of the road. Car overheating is the #1 mechanical cause of summer highway breakdowns, and how you respond in the first 60 seconds determines whether this is a $50 coolant top-up or a $5,000 engine rebuild. This guide explains why cars overheat in summer, exactly what to do when it happens, how to prevent it, and when you need a tow instead of a roadside fix.
Why Cars Overheat in Summer (The 7 Causes)
Your engine generates enormous heat during normal operation — the cooling system’s job is to manage it. In summer, the cooling system is pushed to its limit by hot ambient temperatures, sustained highway speeds, and heavy AC demand. When any part of the system fails or is compromised, the engine overheats. Here are the seven most common causes London drivers encounter.
What to Do When Your Car Overheats (Step by Step)
The next 60 seconds after you notice overheating are the most important. Follow these steps in order — they can save your engine.
Turn Off the AC Immediately
The air conditioning system adds significant heat load to the engine. Turning it off reduces engine strain instantly. Yes, the cabin will get hot — but the alternative is a destroyed engine.
Turn the Heater to Maximum
This sounds counterintuitive — but the heater core is essentially a second small radiator. Running the heater at full blast with the fan on high pulls heat away from the engine and disperses it into the cabin. Open all windows to vent the hot air. This buys you several minutes of cooling.
Pull Over at the First Safe Location
If the temperature gauge is in the red zone or the warning light is on, pull over as soon as safely possible — shoulder, parking lot, side street. Do not try to make it to the next exit or your destination. Every additional minute of driving at extreme temperatures accelerates engine damage exponentially.
Turn Off the Engine
Once stopped, turn off the engine completely. This stops all heat generation. Turn on hazard lights. Do NOT attempt to open the hood immediately — engine components and coolant are extremely hot and can cause severe burns.
Wait 20 to 30 Minutes
Let the engine cool completely. After 20 to 30 minutes, you can carefully open the hood and check the coolant reservoir. If the reservoir is empty or the coolant level is visibly low, you may be able to add water (as a temporary emergency measure) to get to the nearest mechanic.
Assess: Can You Drive or Do You Need a Tow?
If the temperature gauge returns to normal after cooling and adding fluid, you may be able to drive slowly (with the AC off and heater on) to a nearby mechanic. If the gauge climbs back to red within minutes, the engine overheats again, or you see a large coolant puddle under the car — do not drive further. Call (519) 914-3677 for a tow.
🚨 NEVER open the radiator cap on a hot engine. The cooling system is pressurized. Opening the cap releases superheated steam and boiling coolant that can cause third-degree burns to your face, hands, and arms. Wait until the engine is completely cool to the touch — at least 20 to 30 minutes after shutdown. If you are unsure, do not open it at all — call for professional help.
When to Call a Tow vs. When You Can Drive to a Mechanic
After the engine cools, you need to make a decision. Here is the framework.
✅ You May Be Able to Drive
Gauge returned to normal after cooling
Coolant reservoir had some fluid left
No visible puddle of fluid under the car
Mechanic is within 5 to 10 minutes’ drive
Drive with AC off, heater on, monitoring gauge constantly.
🚛 Call a Tow ($150 – $300)
Gauge climbs back to red within minutes
Large puddle of coolant under the vehicle
Steam or smoke still coming from under the hood
Engine made grinding/knocking noises before stopping
A $150–$300 tow prevents $2,000–$8,000+ in engine damage.
When in doubt, call (519) 914-3677 and describe the situation. Our dispatcher will recommend the safest option — a tow or a cautious drive. For a complete decision guide, read our tow truck vs. roadside assistance guide and our signs your car needs a tow guide.
Engine Overheated? Don’t Drive It — Call Us.
A $150 Tow Saves a $5,000 Engine. Every Time.
Tow to your mechanic, your home, or your dealer — 24/7, flat rate, no surcharges.
(519) 914-3677
The Cost of Ignoring an Overheating Engine
Many drivers try to “push through” an overheating situation — driving to the next exit, the next gas station, or all the way home. Here is what that decision costs.
The math is brutal: five minutes of driving with a red temperature gauge can turn a $200 coolant repair into a $3,000 head gasket job. For towing pricing details, see our tow truck cost guide.
How to Prevent Your Car From Overheating This Summer
Every summer overheating incident has a preventable cause. These maintenance habits keep London drivers running cool all summer.
- Check coolant level monthly. Open the hood (when cold) and check the reservoir. If it is below the MIN line, top it up with the correct coolant type. If it drops frequently, you have a leak — get it inspected before summer heat arrives.
- Flush coolant every 50,000 km or per manufacturer schedule. Old coolant loses its heat-transfer properties and becomes acidic, corroding internal components. A $100 coolant flush prevents $2,000+ in cooling system failures.
- Inspect belts and hoses visually. Look for cracks, bulges, and soft spots in rubber hoses. Check the serpentine belt for fraying or glazing. Summer heat accelerates rubber deterioration — a belt that looks fine in April may snap in July.
- Test the radiator fan. With the engine running and warm, the radiator fan should kick on. If it does not, the fan motor or relay may be failing. This is a cheap fix before failure — but an expensive breakdown after.
- Watch the temperature gauge habitually. Make it part of your visual scan while driving — just like checking mirrors. The earlier you notice the gauge rising, the more time you have to respond before damage occurs. According to Transport Canada, monitoring dashboard gauges is a fundamental safe driving practice.
- Do not overload the AC in heavy traffic. In stop-and-go traffic on hot days, consider turning the AC down or off temporarily and opening windows. This reduces engine thermal load when airflow through the radiator is already limited.
For a full pre-trip vehicle inspection checklist, see our summer road trip prep guide.
Where London Drivers Overheat Most Often
Overheating is not random — it happens at specific locations where traffic, heat, and driving conditions converge. Here are the hotspots London Towing responds to most frequently during summer.
401 Construction Zones (Kitchener–Milton)
Stop-and-go traffic at 35°C with full AC running. Reduced speed zones followed by merges. The #1 overheating location for London drivers heading to Toronto. See our 401 emergency guide.
Dundas Street / Oxford Street in Rush Hour
London’s busiest corridors during afternoon rush. Slow traffic with frequent red lights means minimal airflow through the radiator. Vehicles with marginal cooling systems fail here first.
Grand Bend / Beach Traffic (Hwy 21)
Summer weekend traffic jams on Highway 21 heading to Grand Bend. Packed vehicles with rooftop cargo crawling at low speed in full sun — the worst combination for cooling system stress.
Mall Parking Lots After Long Idling
Drivers idling with AC on in parking lots while waiting — especially at Masonville and White Oaks. Extended idling with no airflow puts maximum load on the cooling system.
Other Summer Breakdowns London Towing Handles
Overheating is the #1 summer breakdown — but it is not the only one. London Towing provides the full range of roadside assistance for every summer emergency.
Hot pavement + under-inflated tires = blowouts. $75 – $125 for roadside tire change.
Heat kills batteries faster than cold. $75 – $100 for a battery boost.
AC at full = higher fuel consumption. $75 – $100 for fuel delivery.
Keys locked in car at the beach or park. $75 – $125 for car unlock.
Do Electric Vehicles Overheat?
Electric vehicles do not have traditional engines — but they can still overheat. EV battery packs generate significant heat during fast charging and sustained highway driving. The battery thermal management system keeps temperatures in the safe range, but extreme summer heat can overwhelm it — reducing range, limiting charging speed, and in rare cases triggering a safety shutdown.
If your EV displays a temperature warning, the best response is the same as a gasoline car: reduce speed, turn off unnecessary systems, and pull over if the warning escalates. If the EV shuts down due to thermal protection, it needs a flatbed tow to a dealer — never wheel-lift, as this can damage the electric drivetrain. London Towing uses flatbed exclusively for EVs. For more, see our guide on towing electric vehicles.
Towing & Roadside Assistance Across London
London Towing provides 24/7 towing and roadside assistance across all London neighbourhoods — Downtown, Byron, Hyde Park, Masonville, White Oaks, Old East Village, Westmount, and Lambeth.
We also cover St. Thomas, Woodstock, Dorchester, Strathroy, and the 401/402 highway corridors. Under Ontario’s TSSEA regulations, you choose your tow company. The FSRA provides guidance on insurance coverage for breakdowns. Full services: flatbed, winching, heavy duty, accident recovery, and insurance billing.
Frequently Asked Questions About Car Overheating
What is the most common cause of car overheating in summer?
Low coolant due to a leak is the #1 cause. Other common causes include a failed thermostat, broken water pump, clogged radiator, failed radiator fan, broken serpentine belt, and AC overload combined with slow traffic in extreme heat.
Should I keep driving if my car is overheating?
No. Pull over as soon as safely possible. Even 5 minutes of driving with the temperature gauge in the red can cause head gasket failure ($1,500 – $3,000) or engine seizure ($3,000 – $8,000+). A tow costs $150 – $300 — a fraction of the repair bill.
Why does turning on the heater help with overheating?
The heater core is a small radiator inside the dashboard. Running the heater at full blast with the fan on high pulls heat from the engine coolant and disperses it into the cabin. It is an emergency cooling measure that can buy you several minutes while you find a safe place to pull over.
Can I add water to the radiator in an emergency?
Yes — as a temporary emergency measure only. Wait until the engine is completely cool (20+ minutes), then add water to the coolant reservoir (not directly to the radiator cap). Water does not have the antifreeze/anticorrosion properties of proper coolant, but it will get you to a mechanic safely. Have the system properly flushed and refilled with coolant as soon as possible.
How much does it cost to fix an overheating car?
If caught early: $50 – $200 for a coolant top-up or hose repair. If you drove on it: $1,500 – $3,000 for a head gasket repair. If the engine seized: $3,000 – $8,000+ for a rebuild or replacement. The repair cost depends entirely on how quickly you stopped driving after the temperature spiked.
Is it safe to open the radiator cap when the engine is hot?
Absolutely not. The cooling system is pressurized when hot. Opening the radiator cap releases superheated steam and boiling coolant that can cause severe burns. Wait at least 20 to 30 minutes after the engine is completely off before touching the radiator cap — and only open it with a thick cloth while turning your face away.
Does running the AC cause overheating?
AC alone does not cause overheating in a healthy cooling system. But AC adds significant heat load — and in a vehicle with marginal coolant level, a weak fan, or a partially clogged radiator, the added load of running AC at full blast in heavy traffic can push the system past its capacity. If your temperature gauge starts rising, turning off the AC is the first emergency step.
How do I prevent my car from overheating this summer?
Check coolant level monthly, flush coolant per manufacturer schedule, inspect belts and hoses visually for cracks, test the radiator fan, monitor the temperature gauge habitually while driving, and reduce AC load in heavy traffic. A 15-minute inspection before summer prevents most overheating incidents.
Should I call a tow truck or try to drive to a mechanic after overheating?
If the temperature returns to normal after cooling and you can see no major coolant leak, you may be able to drive slowly (AC off, heater on) to a nearby mechanic within 5 to 10 minutes. If the gauge climbs back to red, there is a large fluid puddle, or steam is still present — do not drive. Call (519) 914-3677 for a tow. The $150 – $300 tow prevents $2,000 – $8,000 in engine damage.
Does London Towing provide roadside help for overheating cars?
Yes. London Towing responds to overheating calls 24/7 across London and all surrounding areas. If a tow is needed, we send a flatbed. If the issue is a simple coolant top-up that allows you to drive to a mechanic, the technician can assess and advise on site. Call (519) 914-3677 and describe the situation.
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