Should I Worry About How Hot My Engine Is Running?

Since an engine can suffer severe damage if it’s run too hot, you should certainly be concerned if there are indications the engine is overheating. But those indications may not be as clear-cut — or come as early — as one might hope.

Related: How to Check Your Car’s Engine Coolant

While a car’s coolant temperature gauge is a good indicator, some cars just have a red warning light that illuminates on the instrument panel if the engine gets too hot. However, that light can sometimes come on too late to be able to do anything about it if you aren’t in a position to pull off the road and turn off the engine right away.

Yet even having a gauge doesn’t do a lot of good if you aren’t paying attention to it. In most cars, normal operating temperature (what the engine should be at after it’s been running for a few minutes) puts the needle at about the middle of the gauge’s scale. “Normal” may be a little higher than that in really hot weather with the air conditioning on, in stop-and-go driving or when towing a trailer, but if you notice the needle climbing past that point, consider it a warning sign that something may be wrong.

What to Do if Your Engine Is Running Hot

If you’ve noticed the needle on the coolant temperature gauge normally hovers near the higher end of the scale or in the red zone, some checks should be done. An engine running hotter than normal can be caused by the coolant level being low (possibly due to a leak somewhere), a clogged radiator, a malfunctioning water pump (which circulates coolant between the engine and radiator), a stuck thermostat (a valve that keeps the coolant circulating in the engine while it’s warming up, then opens to allow it to be pumped into the radiator to be cooled down) or a failed cylinder-head gasket (which could allow coolant to leak into the engine’s cylinders and be blown out the exhaust or run into the oil pan).

If the overheating suddenly occurs while you’re driving down the road, you should try to get the car off the road and shut down the engine as soon as it’s safe to do so. Continuing to drive it can result in engine damage measured in the thousands of dollars.

If you notice the gauge climbing past its normal range or you can’t safely pull off the road, you can try to cool things down a bit by slowing the car, shutting off the air conditioning, opening the windows and turning on the heater full blast. That last part can help because the heater system contains a small radiator called the heater core that’s hidden behind the dashboard; turning on the heat and blowing the fan at full speed may remove some heat from the coolant that also circulates through the engine.

An exception is if it’s cold out and the heat is already on; if so, you should see if you notice a sweet smell, foggy windows and if the carpet in the front-passenger footwell is wet. If that’s the case, the leak may be in the heater core, and turning off the heat (not just the fan) can help, though you’ll have to add coolant to make up for what has already leaked out.

Without question, the best choice at this point is to shut off the engine as soon as possible and have the car towed to a service station. If that’s not feasible, you can shut off the engine, wait for it to cool down for an hour or so, then do what you can of the checks below. In the meantime, you might look to see if there’s coolant dripping from under the front of the car (it could be green, orange or blue), which would point to a radiator, radiator-hose or water-pump leak. If you want to open the hood to do some visual checks — or to notify passing drivers of your trouble — wait to do so until the hood has cooled to the point you can rest your hand on it.

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Things to Check

Once the hood has cooled enough — though perhaps not yet the radiator (tested by being able to hold your hand against the cap) — things to check include:

• Coolant level in the coolant-overflow tank: The overflow tank is often a translucent white plastic jug and is sometimes confused with the similar-looking windshield washer-fluid tank (the latter of which will have a symbol that looks like a windshield wiper and spray of water on the cap). If you’re not sure which is which, follow the hose that runs from just beneath the radiator’s cap to a jug. Look for the fluid level in the jug; it should be between the markings for “hot” and “cold” on the side of the jug. If the jug is empty (you can check for sure by removing the cap and looking inside), the coolant level is low and the coolant leaked out somewhere. Thus, even if you can add more coolant, it would likely be only a temporary fix and likely will leak out again.
• The serpentine belt: This belt is located at the front of the engine, which is likely facing the passenger-side fender in transverse-engine front- or all-wheel-drive vehicles. The serpentine belt is driven by the crankshaft and drives several engine accessories by winding its way around their pulleys. One of those accessories is often the water pump, which won’t turn if the belt breaks or slips and therefore won’t circulate coolant through the engine and radiator. Since the serpentine belt also often drives the alternator and power-steering pump, a broken belt may also cause the battery-charge warning light to come on and make the steering wheel hard to turn. If you see what look like ribbed 1-inch-wide metal pulleys that have no belt around them, the serpentine belt has broken and fallen off. If this is the case, even after the engine cools, it’ll quickly overheat again soon after it’s started.

Once the radiator has cooled to the point you can touch the cap, you can open the cap. Coolant should be all the way to the top of the filler neck; if it’s not, it has leaked out somewhere. (In many cases, if the overflow tank was empty, the radiator level will be low.) Once you have coolant, fill the radiator first, then add to the overflow tank.

If there’s coolant in the radiator or you were able to add some to fill it — and if the serpentine belt is still in place — you can try starting the engine. If there’s a leak, it may not show up until the engine has reached operating temperature, so be mindful of that if you’re trying to get the car home or to a shop. If your car does have a leak, keep an eye on the temperature gauge.

While there are other checks that can be done when you’re home or performed by a shop, those take more expertise and include checking for:

• Leaks: These may show up only after the engine has warmed up and could come from the water pump, hoses, radiator or heater core behind the dash.
• Whether the thermostat is opening: If the coolant temperature gauge indicates the engine is warm but the upper radiator hose is not really hot (be careful not to burn yourself), that’s an indication the thermostat may not be opening as it should.
• White exhaust smoke: Coolant leaking through a failed head gasket into the cylinder will be burned along with the air-fuel mixture, creating white exhaust smoke.
• Whether the fan is turning: Many newer cars — and virtually all with a transverse (sideways-mounted) engine — have an electric cooling fan rather than one that’s driven by the engine. If the engine is running warmer than it should be, the fan should be spinning. You can usually hear it.
• Coolant in the oil: Also due to a head-gasket leak, coolant can run into the oil pan. One indication of this is that the oil level is mysteriously high. Another is that the oil on the dipstick will be sort of a frothy tan color, which some describe as looking like a chocolate milkshake. Your engine can be severely damaged if run with coolant in the oil.
• A clogged radiator: Unfortunately, this is a bit difficult to determine and might best be left to a professional.

Since an overheated engine can be a serious problem, watching for coolant leaks,  keeping an eye on your coolant temperature gauge and preventive maintenance — such as changing your coolant when recommended and checking belts and hoses periodically — can be well worth the trouble and expense.

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