How to Diagnose and Fix an Overheating Vehicle

We all love upgrades. The kind of mods that make your car or truck faster, lower, better looking. But while you’re dreaming about horsepower and the perfect stance, there’s one thing that’s easily overlooked: the engine cooling system. Not sexy, but when it goes bad, you’re toast—literally.

Before your ride becomes a rolling sauna, here’s your no-nonsense guide to spotting and fixing cooling issues. Whether you’re cruising Route 66 or idling in Friday-night traffic, here’s how to stay chill behind the wheel while keeping your ride chill under the hood.

First, Is It Really Overheating?

Before you dive into troubleshooting, it’s worth asking: Is your vehicle actually overheating—or just running hotter than you’re used to? There’s a big difference.

Overheating means your engine is pushing coolant out, either as steam from the radiator cap or as liquid spilling through the overflow. That’s a problem, and one that needs fixing.

But if your engine is running warm without losing coolant, you might just be dealing with modern engine behavior. Here are a few things to keep in mind:

1. Today’s Engines Run Hotter by Design
   If you’re used to vehicles from the 1980s or earlier, 210–220 degrees Fahrenheit might sound like a red alert. But in modern engines with electronic fuel injection, that range is completely normal. In fact, some EFI systems won’t even switch into closed-loop operation until the coolant hits around 190–205 degrees.
2. Better Seals and Higher Pressure
   Along with higher temps, newer engines also run higher pressure in the cooling system – typically 16 psi or more. That helps keep coolant from boiling or escaping even as temperatures climb.
3. Sensor Location Can Skew the Reading
   In older vehicles, the temperature sender was usually located in the intake manifold. These days, most sensors are located in the cylinder head between the exhaust ports where temperatures are naturally hotter. That simple shift in location can add 10–15 degrees to your gauge reading without changing the actual operating temperature of the engine – and cause unnecessary worry if you don’t realize it.

So before assuming there’s a problem, it’s worth checking whether your system is actually overheating – or just doing exactly what it was designed to do.

Really Overheating? Start with the Timeline

Like a mystery novel, your cooling issue has a backstory. Ask yourself:

• Did it start after you added power? (More power = more heat.)
• Did you route your transmission cooler into the radiator? (That’s a heat dump.)
• Did you not change anything at all? (Could just be old parts tapping out.)

Let’s break down the usual suspects.

A great cooling system isn’t as sexy as a 6-71 blower, but you’ll certainly appreciate the cooling system for keeping you off the side of the road watching steam escape from your classic-car engine bay.

1. Thermostat

If your engine runs hot sometimes but not others—or suddenly starts acting up—the thermostat might be sticking. It’s supposed to let coolant flow once your engine warms up. But when it fails, it’s like a traffic jam in your cooling system. Swapping it is cheap insurance.

Pro tip: Replace it if it’s older than your favorite concert T-shirt.
Inexpensive and old thermostats have caused untold volumes of sorrow for car enthusiasts.

2. Radiator Cap

This humble little part might not look like much, but it’s the pressure cooker lid and relief valve of your cooling system. If it has a cracked seal or tired spring, it won’t hold the pressure it is supposed to, letting your coolant boil sooner than it should. Check the rubber gasket, test the spring. If it feels sketchy, toss it.

3. Radiator

If your car or truck is overheating all the time or at highway speeds, your radiator might be clogged, corroded, or undersized for your setup.

And don’t fall for the “more cores = better” myth. A four-core radiator might hold more coolant, but it can choke airflow. Today’s smart money is on efficient two-core aluminum radiators with wider tubes – they transfer heat better and breathe easier.

While brass and copper radiator construction is ideal for heat transfer, most performance aftermarket radiators feature 2-core construction with larger tubes. This provides good coolant flow and volume while letting a fan pull air through the radiator more easily than is possible with a 4-core radiator.

4. Water Pump

This is the pump that keeps the coolant party going. If the bearings or seals are worn or the impeller is clogged, flow drops and your engine pays the price. And don’t cheap out here – a bargain-bin pump can cause cavitation (think: blender full of air bubbles) that creates hot spots and leads to real trouble.

5. Fans

When you’re stuck in traffic, your fan is the only thing keeping your engine from sweating bullets. If overheating only happens at low speeds, your fan setup may be underachieving.

Electric fans need to move at least at least 2,500 cfm for most street builds. For heavy towing or high-performance engines, you’re looking at 3,000–6,000 cfm.

And if you have a belt-driven fan, make sure it’s paired with a proper shroud. No shroud means hot air just flutters around like a weak breeze on a summer day. But back to being stuck in traffic – you need an electric fan in that situation. The belt-driven fan just can’t move enough air at idle and slow vehicle speeds to keep the car cool.

Electric fans solve the idle and slow-speed overheating that is so common at car shows, cruises and long-haul road trips.

Bonus Tip

Whether electric or mechanical, your fan needs to pull air across the whole radiator. That’s why full shroud kits work wonders—they make sure every square inch of radiator is doing its job, not just the middle.