What to do if your engine is overheating

How to decide what to do when your car overheats

Overheating is really bad news and can quickly cause serious and costly damage to your motor. When is it safe to let the car cool down and drive to the shop and when should you call a tow truck? What you decide can mean the difference between a relatively minor repair and shopping for a new car. In this short post I’ll explain your options and how to determine what you should do.

“Mild” overheating

By mild overheating, I mean that the temperature gauge is reading higher than center, but it’s not in the red. This isn’t normal, and you should have your mechanic take a look, ASAP, but you don’t necessarily need to stop driving. Mild overheating is usually caused by one of two things:

  1. If the car is getting warmer in stop and go traffic, it’s likely an issue with the cooling fan. When the car isn’t moving, there’s no air flow over the radiator and a fan is necessary to keep the system cool. If it stops working, the temperature will climb at slow speeds and then cool down once you get moving again. Sometimes turning on the air conditioning can help. On some cars, with some types of fan problems, turning on the AC will get the fan(s) spinning again. However, this will vary car to car and the AC can also make the problem much worse. A part of the AC, called the condenser, sits in front of the radiator and when the AC is on, it gets hot, making it harder for the radiator to remove the heat from the engine coolant. The best thing you can do is take a route that allows you to keep the car moving and check the temperature gauge regularly. If it gets close to the red, give up and call for a tow.
  2. If the car is getting warmer when driving up hill, especially on the freeway, poor coolant flow is the most likely cause. The most common cause of poor flow is a restricted radiator. If the gauge only reads warmer when driving up hill, but then cools down when the engine isn’t working very hard, suspect the radiator, thermostat, or in rare cases, the water pump. The best thing to do in this case is to turn on the heater to full hot. There’s a little mini-radiator under your dash that provides the “hot” for your heater. When you run the heater the blower cools it down and removes heat from the coolant.

Beware of low coolant!

Low coolant can prevent the gauge or light from warning you when the engine starts to overheat which can be really dangerous. Imagine holding a thermometer over a pot of boiling water. You won’t read the temperature of the water because air doesn’t transmit head as well as water because it’s less dense. Cars almost always have the temperature sender (like a thermometer) at a high point in the cooling system. Heat rises, and the engineers want to know what the temperature is at the hottest point in the system. That’s all great until the coolant level drops. When that happens your gauge may say everything’s OK when it absolutely isn’t. You won’t see the gauge rise until the engine is extremely hot and the coolant is boiling.

The obvious solution is to check the coolant, but BE CAREFUL. Your cooling system is under pressure to increase the boiling point of the coolant. Just like a pressure cooker. If you open the radiator cap when the system is hot, you may be badly burned. This can happen when the car is warmed up, but can be much worse if the car is overheating. If you want to try to cool the car faster, it’s OK to spray water into the grill between the headlights. Don’t spray water under-hood though.

Major Overheating

If the gauge is reading in the red, or steam is coming from under the hood, call a tow truck. Yes, it can ruin your day. It can ruin other people’s day. It can make your boss mad. And who knows what else.

Here’s the thing: major engine repairs are really expensive these days. Modern engines aren’t huge chunks of cast iron that can be re-machined and rebuilt several times. Most only have one life. Cylinder liners are literally sprayed in place and are only 1mm thick. There is no boring and honing. Cracked heads can’t be welded anymore We just throw parts in the scrap bin and buy new ones — and they’re not cheap. Buying the parts necessary to repair a badly damaged engine can cost $8000, and that’s without and labor. The best solution is to not damage the engine. It’s always better to be safe than sorry when it comes to overheating.