Help coolant problems

[philip1952]

Hi For the past couple of days after i have driven for about an hour the coolant light on my A3 has come on. I have stopped the car to find the coolant level was low. The funny thing is that when i releave the cap the coolant returns to the normal level. Coolant is not being lost so I am assuming it is not a leak. Could this be expensive???

[ok2000A8]

When you release the pressure on a pressurized system at elevated temperature, the hot liquid can expand (as it wants to) now that the pressure is released. If you would wait for liquid to cool after you reseal the overflow container, you'd pull a vacuum in the container possibly collapsing the container. That's just thermodynamic properties in action that you're witnessing. You'll also notice both a "Minimum Cold" level indicator and a "Maximum Hot" level indicator on overflow container. If engine is hot, do not open container but look at fluid level. If it's not right at level of "Maximum Hot" level, then you'll ned to add fluid. Also check level when cold and be sure that level is at level or just a bit above. There may also be a "Minimum Cold" level which you always be above - hot or cold. Indicators and labeling depend on year and model of car.

Bottom line - not expensive - add some antifreeze-water mix 50-50 for top up is okay.

[mikeh]

Quote:

Originally Posted by ok2000A8

When you release the pressure on a pressurized system at elevated temperature, the hot liquid can expand (as it wants to) now that the pressure is released. If you would wait for liquid to cool after you reseal the overflow container, you'd pull a vacuum in the container possibly collapsing the container. That's just thermodynamic properties in action that you're witnessing. You'll also notice both a "Minimum Cold" level indicator and a "Maximum Hot" level indicator on overflow container. If engine is hot, do not open container but look at fluid level. If it's not right at level of "Maximum Hot" level, then you'll ned to add fluid. Also check level when cold and be sure that level is at level or just a bit above. There may also be a "Minimum Cold" level which you always be above - hot or cold. Indicators and labeling depend on year and model of car.

Bottom line - not expensive - add some antifreeze-water mix 50-50 for top up is okay.

Great write up and accurate.

Are you finding any liquids under the car when either left for a while or immediately after you stop? One of the common problems is the overflow container mentioned above can develope a small leak at the seam. You may not notice this right away. Do your checks as mentioned earler and see what the levels are. Then add as appropriate and monitor that. If its the container then no its not expensive.