Is this normal? Pressure in coolant overflow tank

[elmosisu]

Hello, all...

I had a question on if my coolant reservoir tank should have any pressure in it when the engine is up to temperature?

I went to check the level ( after seeing posts about the possibility of leaking hoses ), and noticed that the coolant was at the MIN line of the tank. I figured that I'd top it off with a little 50/50, and upon opening the tank, I got a pretty good rush of pressure, and the tank actually shrank back down to where the coolant line was back to where it should be.

Is this normal?

[SmartJoeMN]

Yes that is normal. The cap to the reservoir tank is just like a radiator cap.
Check when the engine is cold and be careful out there

[Carbon Brabus]

My smart always had pressure in the tank after it was warmed up too! You should only add coolant (if needed) when the engine is cool.

[elmosisu]

Thanks, all...... I'm used to vented reservoir tanks from my older cars and motorcycles.

[Padawan]

Just make sure you firmly tighten the cap after you're finished. I recall at least one member experienced catastrophic overheating due to a reservoir cap that wasn't properly tightened.

[forestacademy]

Thanks for the reminder, Just checked, but can't really tell where the low mark is on the tank. But it defiantly is not way down.

[Padawan]

The low mark is right at the "seam" between to top and bottom half of the reservoir.

[forestacademy]

Originally Posted by Padawan

The low mark is right at the "seam" between to top and bottom half of the reservoir.

Then what are all the marks below the seam?

[Padawan]

Just part numbers and such.