I had a had to replace my engine because it overheated. The mechanic just changed the engine and said overheating was the cause without saying whether there was any leaks etc.

Since yesterday I noticed the in car heater wasn't heating up. I checked the coolant reservoir and it was showing as below the minimum. I drove it and it was sluggish the whole day. i wasn't observing the temperature gauge to know if it overheated or not.

Took to mechanic they identified leak from radiator and said the thermostat also needed replacing and so am just about to get the work done.

My question is, how do I know that as a result of driving whilst the engine had aforementioned symptoms and was sluggish, how do I know it hasn't been damaged i.e. there isnt already engine damage or a burnt head gasket. Could the sluggish movement be a symptom of engine damage?

I asked the mechanic this and he said the 'engine sounds ok just change the radiator and thermostat and you should be ok'. Is this sound advice or can I expect to be paying for more repairs after this work is done. I've been here before and it cost my through the nose. Should/can they look for engine damage before engaging in the current repairs as I've already spent too much from previous jobs and if there's engine damage, might be better for me to dispose of it.

  • Since your heat wasn't working very well, I think it's safe to assume that your engine did not overheat.
    – JPhi1618
    Nov 29, 2017 at 15:40
  • 2
    I disagree @JPhi1618, your car can overheat while the heat stays off if there's a problem with the coolant circulation or the heater matrix.
    – GdD
    Nov 29, 2017 at 19:13
  • If you get this repaired,make sure to turn the heat full on and observe the coolant level. Heating should be normal - if it is not, your cooling system has not been bled correctly. On some cars, this is quid hard to do and air-bubbles in your cooling system can render it ineffective.
    – Daniel
    Nov 30, 2017 at 15:24
  • @Daniel sorry i don't get this. Do you mean i should turn heater on full, rev it, remove radiator cap, and look for what in the coolant level? btw i asked a separate question on why my heater isn't coming on when stationary. Dec 1, 2017 at 17:57
  • @James Wilson: The car heater is actually just another cooler usually somewhere behind the glove compartment. Your car regulates the heating by allowing more or less coolant to flow to this second cooler and thus heating your air more or less. If heater is turned off, no coolant flows through and Air can be trapped in it. Once the Air is out, it needs to be replaced by more coolant. Some Cars also have bleed-valves to get the air out, which are often quite hard to spot in a dirty engine bay.
    – Daniel
    Dec 1, 2017 at 18:43

2 Answers 2


Overheating can cause your head to warp and / or the head gasket to blow. Either of these will lead to a loss of compression. As long as the compression is fine, fill up the coolant, fix the leak.

Compression test. This involves a compression test gauge inserted into the spark plug hole and see how much compression the cylinder makes. There is a low threshold you should be above, and a variance there should be between the cylinders.

Another way is to: allow the engine to cool, remove the radiator cap, start the car. If the coolant is bubbling, the head gasket is blow.

If your oil or coolant look like a nasty milkshake, your coolant and oil are mixing, likely due to a blown head gasket.

Excessive smoke from the exhaust can result form a blown head gasket. It will smell sweet like coolant.


If you overheat the car, you will experience one of those

  1. Coolant loss over time white/gray smoke out of car exhaust.
  2. Burning oil black, dark grey or blue smoke coming out of car.
  3. Loss of compression car won't even start.

If you don't experience any of those your car is fine.

  • The coolant went below the minimum level. White/grey, dark grey\blue smoke, burning oil coming out may have happened but i didn't notice. Car does start but is sluggish moving(could this be loss of compression?). Are you suggesting the sluggish movement can be caused by little coolant and not an overheated engine? is there no way to know at the moment and so i need to get the radiator and thermostat replaced before any engine inspection? thanks Nov 30, 2017 at 7:25
  • Best way to check if your car is okay is to remove the head, inspect the engine and check if the head is dented. Other way is just rev the car and check out the window if there is any smoke, if there is unusual color or amount of smoke you are in trouble. If you can't rev and look at smoke at same time ask someone to do it for you. Loss of compression can cause car to lose power or not start at all it depends how much compression is lost.
    – AsenM
    Nov 30, 2017 at 7:30

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