What to do with steam coming from the hood

What To Do When Your Car Overheats

Seeing steam billowing from under the hood is the worst possible thing that can happen to any driver, barring only fire and an accident. What to do? Do you continue driving and hope the steam clears, or do you simply ignore the steam, since there is not much of it? There are several things you should do, and the first is to confirm that the engine is in fact overheating. If it is overheating, the temperature gauge will register a reading above normal, and the check engine light may be illuminated.

So far so good- you have established that the engine is overheating, but it could shut off at any moment, so before it does, do the following:


  1. Switch off the air conditioner to reduce the load on the engine. Depending on how high the temperature gauge is registering, turning off the A/C will buy you a few seconds to exit the traffic before the engine shuts off. If the temperature gauge registers above normal, but is not yet in the red, danger zone, turn on the heater at its highest setting. This will divert some of the superheated coolant through the heater’s heat exchanger, and it might buy you some more time to find a safe spot to stop before the engine shuts off.
  2. Once you have stopped safely, and do not present a danger to passing traffic, switch off the engine to prevent further damage. At this point the engine is already damaged, but there is a good chance that if it is allowed to cool off, it might have enough life left to get you home. Now would also be a good time to call for assistance.
  3. If it is safe to exit the car, it will help to open the hood to speed up the cooling process, but do NOT open the hood while steam continues to emerge from the hood and grille. For all you know, there may be one or more jets of superheated steam spraying in all directions and if you get a blast of steam in the face, you will end up scarred for life.
  4. As soon as the steaming stops, open the hood very carefully because there may still be boiling coolant squirting out of ruptured hoses and pipes. Confirm that there are no jets of boiling coolant to disfigure you before opening the hood fully. At this point the engine will be too hot to do anything, so prepare to wait for at least an hour before you touch anything to avoid burning yourself.
  5. Resist the temptation to start the engine to see if it still works. It may be partially seized because of the excessive heat, and if you start it now, you will only add to the damage as the pistons tear themselves loose from the cylinder walls. Of course, this does not matter if your insurer is going to pick up the tab to have your car towed to a repair shop, but it definitely matters if you need the car to get home.
  6. Ideally, the car should not be driven, but if you are in an emergency situation and you need to get home, you must now assess the damage. There are several things that could have caused the overheating, such as a loss of coolant through a ruptured hose, a punctured radiator, a defective thermostat, a defective radiator cooling fan, or a blown cylinder head gasket.

    Chances are excellent that if the head gasket did not cause the problem, it will have been destroyed during the overheating. However, this does not always happen, so the thing to do is to look for obvious signs of a major leak. If the engine is cool enough to touch, inspect the radiator hoses and the radiator itself for signs of damage. If these items check out OK, the cause is either a defective cooling fan or thermostat.
  7. If there was no coolant leak, the cooling system may still be under some pressure, so wait for the engine to cool down completely before removing the radiator, or expansion tank cap. If there is still coolant in the system, take a good sniff around the filler cap- if the coolant smells like exhaust gas, the head gasket is blown. If this is the case there may, or may not be oil mixed with the coolant, so the absence of oil in the coolant does not mean that head gasket is not damaged.
  8. Next, pull out the dipstick, and check to see if there is coolant in the oil. This will manifest as a milky-white emulsion on the dipstick and on the inside of the oil filler cap. If the dipstick and oil filler cap are clear there is no coolant in the oil, and you might just make it home yet. By this time though, the engine will have cooled down sufficiently for you to fill the cooling system with water. There is no point in worrying about anti-freeze now; if you have access to water, fill the radiator with water, but do not replace the radiator cap.
  9. You can now try to start the engine, but one of four things will happen: it may refuse to start, it may start but run roughly, it may start but the coolant may be expelled from the system by the pressure-leak through the head gasket, or it may run without even a misfire- a rare occurrence, but it does happen.

    If the engine does not start, it is not going to start, so you are stuck. If it starts, but expels the coolant, you are also stuck because it will overheat again within a few hundred yards. However, if it starts and does not expel the coolant, but misfires, you have a fighting chance to drive the car to the nearest repair shop, or home if you live close by- provided the radiator fan still works.

It sometimes happens that an engine runs well for several thousand miles after an episode of serious overheating, but such an engines’ days are numbered. The piston rings will have lost their spring tension, the engine oil will have lost its lubricity, the head gasket will have been damaged, the automatic transmission may have suffered damage, and the water pump bearings will have suffered a loss of temper, or hardness. All of these things are bad, and expensive to repair or replace.

The better option is to replace or rebuild the engine as soon as possible after an overheating episode, and to hope it does not happen again- which of course it could at any time, but next time you will know what to do.