I know that a lack of engine oil can destroy an engine, so I was curious as to whether it is just as bad to drive a car with a very low engine coolant.

What is engine coolant?

What exactly are all of the disadvantages to running an engine when the engine coolant becomes too low?

  • Depends on how hot, how long, and what vehicle. For example a VW bug has no coolant.
    – Xeno555
    Commented Jan 16, 2016 at 7:41
  • I had a very bad experience when I was just starting to drive...failed to check the coolant, ran dry when I was in the expressway...97 Ford Expedition, body started to shake, a few hundred meters to home, truck loses power, a hundred meters away, truck moves in a turtle pace...at the parking area, can't reverse, panic sets in, turn off engine, starts again and can back up...just a description of what to expect when you ran out of coolant...
    – MhykGyver
    Commented Aug 4, 2017 at 13:18
  • Do you mean a low level of coolant to water mix (i.e. supposed to be mixed 50:50 but is 70% water?) or do you mean the level of liquid in the coolant system is below the minimum mark? Commented May 7, 2019 at 11:46

6 Answers 6


What is engine coolant?

Engine coolant is a water and antifreeze solution. Because water has good properties as a coolant, antifreeze is used in internal combustion engines and other heat transfer applications, such as HVAC chillers and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from bursting due to expansion when water freezes.

Cooling System

As the coolant is moved around the system by the water pump, it passes through two main components:

  • Radiator - The cars air intake is used to dissipate heat (which is easier across a larger surface area, higher fin density and thicker radiators - much like in PC water cooling). This is able to keep the engine coolant cool.
  • Engine Block - This is the main part that the coolant is designed to wick away heat from, by flowing through engine hot spots and allowing the heat to transfer from the engine oil to the coolant as well in the process.

What exactly are all of the disadvantages to running an engine when the engine coolant becomes too low?

Just to clarify, there are no tangible advantages other than saving a tiny amount of money on engine coolant. As you will see, you should never do this due to the knock-on effect that it can cause.


Depending on the make and model of your car some of these may not apply, but in general:

  • Water pump running dry - They will destroy themselves very quickly without water in them as they are not designed to run without lubrication and sufficient resistance (much like the pump in a water cooled PC).
  • Overheating - this is the main disadvantage, but this can cause a huge knock-on effect in terms of causing other damage within the engine. These include but are not limited to the following:
    • Seized piston - The piston will expand marginally due to the heat. As the engine uses such fine tolerances, this expansion can be enough to make the piston rub hard on the cylinder casing and make the crankshaft grind to a halt! This will be very expensive to fix.
    • Hole in the engine block - Realistically however, a lack of coolant will not cause a hole in the block. It could be caused from a thrown rod, which occurred because the piston in the engine seized during operation.
    • Warping of head(s) - This can cause the head gaskets to lose integrity.
    • Interior car heater will lose functionality - The heater functions based on the engine coolant, as seen in the diagram above.
    • Transmission failure - In some cases the transmission fluid cooler is internal to the radiator, meaning that a lack of engine coolant can not only cause the engine to overheat, but also the entire transmission.
    • High pressure in hoses - Radiator/Coolant hoses can burst due to the increased pressure in the cooling system.
    • Cost - To fix the damage already done to the engine at this point, it will be very expensive and you could probably justify buying a new used car instead!
  • Also THERE IS ADVANTAGES running with lower coolant amount. In winter car gets warm faster, warmer coolant at winter = MANY MANY MANY advantages. Just need to watch that thermostat wont stay open all the time so there wont be overheating when car gets more load.
    – Tommixoft
    Commented Dec 1, 2017 at 1:31

You get less cooling. If the radiator is only 1/2 way full you have water in contact with cooling fins for 1/2 the time and 1/2 the cooling. The fluid is pumped from bottom so it will continue to flow. Eventually the water is hot enough that the engine turns it to steam. Once you empty the radiator then zero cooling as nothing is pumping.


Water flow will stop and the heat will not be able to be transferred out of the engine block. Engines cooling systems are very intricate and feature "pockets" depending on how much cooling is needed for a given area. A lack of coolant means that the system will not be able to be pressurized by the pump and the coolant will not flow.


  • Overheating

  • Water pump running dry and damaging itself in the process for a lack of lubrication and resistance

  • 1
    The disadvantages.... 1) overheating 2) seized piston 3) blow a hole in the block 3) warping of head(s) 4)heater doesn't work 5)transmission failure (trans-fluid coolers are sometimes internal to the radiator) 6)....
    – Dee
    Commented Jan 16, 2016 at 2:46

My sons 99 LS1 Trans Am started to lose power after running fine to the last gear but then it would lose power and run the rpms 2000 at 35 mph. Yesterday, he stopped on the side of the road because it had a smell like something burning and a little bit of greyish smoke was coming from the back. He let it cool and made it home. No more smoke. When the mechanic looked at it today, there was very little coolant/water in the radiator. He told him that with the low coolant it was telling the transmission it was getting too hot and therefore it wouldn't go faster. He said that smell was burning coolant. He put coolant in it and they took it out up and down the highway and let it warm up and he got on it and it went through all the gears and had plenty of pickup. The mechanic said it should be ok now but keep an eye on it. I told him to watch for any leaks under it when he parked it because the radiator or a hose could have a leak. I am hoping he dodged the bullet with it and will keep up with making sure it has coolant. Im guessing that if the head gasket or block were damaged, there would be some signs. The transmission is shifting smoothly through all the gears.


As the coolant gets lower and lower things will progress as follows:

  1. There won't be coolant in the coolant expansion tank even when the engine is warm.
  2. There will often be insufficient fluid to circulate coolant through the heater core and the heat won't work. A water cooled throttle EGR / body could suffer too.
  3. The water pump will pump most of the water out of the radiator and there will be insufficient coolant flow, and the temperature gauge will show higher than normal coolant temperature under heavy load.
  4. #3 will get worse
  5. There will no longer be sufficient coolant to circulate coolant. The temperature gauge could show too low of a temperature due to lack of coolant coming out of the engine. The coolant will start to boil and then it will condense on the temperature sensor and it will show hot. The engine will over heat.
  6. There won't be enough coolant to fill the cylinder head. The temperature gauge will report too low of a temperature. The cylinder head will over heat and it could lead to damage like a warped head. Eventually the block will heat up and it will boil off coolant and the temperature gauge will show high temperature, but it could be too late. The high head temperature can cause pinging or knocking from pre-ignition. Shut it off now and the head can be saved.
  7. No coolant - the engine will be severely damaged in a matter of minutes if run under load. The temperature gauge will report too low of a temperature since there is no coolant, as the temperature sensor will likely not heat up fast enough to show the true engine temperature and let the driver know to shut off the engine until it's too late. Noticing that the temperature gauge is too low, or hearing pinging can be an indication to shut off the engine to prevent more than minor damage. Some vehicles have a cylinder head temperature sensor that isn't dependent on coolant. The vehicle may go in to limp mode.

Some engines require purging to remove air pockets from the cylinder head after the coolant level is restored. This may require revving the engine up momentarily.

Engines with aluminum cylinder heads on iron blocks are highly susceptible to head gasket damage when over heated, due to the differing rates of expansion of the different metals. Avoid running them even if the temperature gauge shows a minor overheat.


NOTHING will happen if that lower amount wont cause overheating. For example in my country winters are very cold about minus 32 degrees Celsius. My car to get warm it takes about 30 minutes. It's Italian car and it very bad at warming up in winter. So i use less amount of coolant so this amount heats faster. And impossible to overheat car because when thermostat opens cold coolant from radiator makes coolant cold again and car never overheats. People here just makes worst scenarios. witch is not possible if your coolant temp is in normal range - 90c. Also fairy tales about water pumps is stupid. Water pump is just bearing that is driven by belt. Bearing rotates plastic stuff that makes water flow. Maybe in other cars it's different in mine there is no actual pump. SO if there would be no coolant, which is impossible based on your question - it wont broke.


  • This is a poor idea. Lower-than-spec coolant levels may lead to localized hot spots in the motor, and consequent damage. Failure to warm up would be caused by other things, e.g., a defective thermostat that has "failed open." Commented Nov 12, 2019 at 20:00

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