Checking the coolant level

[zimmerDN]

Do you check the coolant level when the car is cold, warm, or hot? I notice the level could vary so much that when the engine is hot it would be at the full level and when the engine is cool it's slightly below and then when the engine is cold it's below the fill line.

Why? I understand pressure builds up as the liquid heats up but does it also expand in volume? So does car need more coolant?

 

[sifan]

The coolant level in the radiator should be always at the full level even when the engine is cold. That is what coolant overflow tank is for.

 

[ConfederateTyrant]

Check and make sure yours does not have a "Full Hot" and "Full Cold" level to check. If it just says "Max" and "Min" without designating hot or cold, then fill it to the "Max" level.

 

[unDummy]

If you have a standard normal overflow/recovery bottle, fill 'er up. Most are vented and will spill any excess when hot.

If you have a pressured degassing bottle that can only be filled when cold, then make sure that the coolant level is perfect full/max cold as mentioned by Confederate.

I actually had 1 vehicle, with the degassing pressured bottle, that I attached a standard recovery bottle. This allowed me to fill the degas bottle to the top and let it vent PSI into the recovery. It fixed a factory screwup which allowed the degas bottle to burp too much coolant during traffic or summer heatwave. After burping coolant, the engine would be low on coolant, and develope air pockets which would lead to overheating and eventually popped head gaskets.