Coolant leaks. An overheated engine. Slow warmup.

These are three conditions that indicate, or likely indicate, a problem with your cooling system. We’ve put together this quick guide to help you track down cooling system issues and avoid getting stranded on the side of the road. And what’s worse than that, really? It’s like the walk of shame for car guys—except you’re going absolutely nowhere.

Coolant Leaks

Coolant leaks can be internal or external.

Typical external leaks show up as stains at the leakage point or puddles on your driveway. They usually come from one of these areas: radiator hose, hose connection, radiator core, heater core, or water pump shaft.

Internal leaks usually occur when coolant seeps into some other part of the engine. Although you typically can’t see an external leak, some signs of an internal leak include white exhaust smoke or frequently having to add coolant to your vehicle. An internal leak can damage or even kill your engine and should be addressed immediately. Here are some some possible causes and solutions for coolant leaks:

Possible Cause #1: Pressure cap and gasket defective.
Solution: Inspect, wash, and pressure-test the cooling system. If the cap does not hold pressure, replace it.

Possible Cause #2: Leakage within the core.
Solution: Pressure-test your radiator and replace if leaking.

Possible Cause #3: External cooling system leaks.
Solution: Perform an inspection of all hoses, connections, gaskets, core plugs, drain plugs—anywhere fluid travels within the cooling system. Replace any components as necessary.

Possible Cause #4: Internal cooling system leaks.
Solution: Check the cylinder head bolt torque and adjust as necessary. If this does not solve the problem, you may have to disassemble the engine, checking for a cracked intake manifold, blown head gasket, cracked or warped cylinder head, or even a cracked engine block. These items will need replaced as necessary.

Engine Overheating

First and foremost, your engine may overheat for reasons other than a faulty cooling system. These reasons may include low oil level, engine overload, improper ignition timing, or simply an extremely hot environment. For this post, we’ll focus only on possible cooling system troubles.

If you’ve got a high performance vehicle, we’ll assume you already have the proper radiator and fan in place. If not, read our Aftermarket Radiators 101, How to Choose and Aftermarket Radiator, and How to Choose an Electric Fan in 4 Easy Steps posts. That being said, here are some possible cooling system causes for overheated engines.

Possible Cause #1: Low coolant level due to leaking.
Solution: Follow the steps outlined above.

Possible Cause #2: Accumulation of rust or debris within the cooling system.
Solution: Any debris within the components or pathways of the cooling system will prevent coolant from circulating. Follow your manufacturer’s recommendations for flushing your cooling system on a regular basis. You can do a quick-check of the coolant by removing the radiator cap and wiping the inside of the filler neck with your finger. If you see grease, rust, or debris, you’ll ned to perform a radiator flush.

Possible Cause #3: Collapsed hoses.
Solution: Needless to say, collapsed hoses will prevent coolant from circulating properly. Inspect all hoses by simply giving them a squeeze. They should not collapse easily, so replace any hose that is soft, brittle, rotted, or swollen.

Possible Cause #4: Loose or worn drive belt.
Solution: Do you hear a high-pitched squeal while your engine is running? This is often the sign of a loose or slipping drive belt. A drive belt that slips will not turn the water pump at normal speed, and the pump will not be able to flow coolant fast enough to keep up with the engine’s cooling needs. With the engine off, inspect the drive belt for stretching, cracks and other wear and make sure it has the proper tension using the belt tensioner.

Possible Cause #5: Themostat stuck closed or otherwise defective.
Solution: If the engine overheats without the radiator becoming warm (and if there’s no slippage at the drive belt), there’s a good chance the thermostat is defective. The defective or stuck thermostat essentially blocks coolant from flowing to the engine and will need to be replaced. Once you’ve replaced the thermostat, retest the system to confirm the fix.

Possible Cause #6: Defective water pump.
Solution: A defective water pump simply won’t flow enough coolant. Often, bearing failure is the culprit behind a faulty water pump. The first sign of bearing failure is often a noisy water pump, but you can confirm this by removing the drive belt and moving the mechanical fan. Any movement in and out, or a grinding sound when turning the fan, indicate defective water pump bearings. You will need to replace the water pump.

In some cases, you engine may experience something called “afterboil.” This generally occurs after the engine has been shut down after a long drive, and the heat buildup from extended use causes the coolant to boil.

Slow Warmup

The most likely cooling system culprit for slow warmup is the thermostat. If the thermostat is stuck open, it will allow coolant circulation to the radiator even when the engine is cold. This means the engine has to run longer to warm up.

You may ask: “Other than testing my patience, does slow warmup really matter?”

Slow warmup can lead to the formation of engine sludge, increased exhaust emissions, and quicker engine wear. It can also mean your vehicle heater will take longer to warm up—a big deal when Old Man Winter makes his appearance.

Possible Cause: Missing thermostat or thermostat stuck open.
Solution: Fire up your engine. While the engine is still cold, squeeze the upper radiator hose. NOTE: KEEP YOUR HAND AWAY FROM THE FAN! At this point, no coolant should be flowing through the hose. If there is, the thermostat is either missing or stuck open.