Is the coolant level dropping this much overnight normal?

Is this normal level of coolant dropping over night? I have a 2008 Tundra SR5 4.7

I took my truck into the shop for leaking coolant, they said an o ring was bad and replaced it. Said it should have fixed it. I took one pic at 7:30pm (The pic with more coolant in the res tank) And the other pic was taken at 9am the next morning. Is the level dropping that much overnight normal? It was cold over night as well. I’m currently running my truck to see if the level goes back to the top or not. Can’t really see any wet marks under the truck as well. So worried about a blown head gasket or something.

 

I just took this pic. I’ve let the truck run for about 30ish mins and it’s back to the top. So is that normal?

 

Fluid expansion and contraction. Hot fluid expands, so reservoir is fuller when hot. Cold fluid contracts, so it will draw in coolant from the reservoir

 

Give it a little time. I've seen the large swings after changing coolant or opening up the system like a water pump change. My Fiat 124 still shows enough difference with ambient temperature changes I could almost use it as a thermometer.

 

As said looks like normal expansion. Look at it two mornings in a row after it has sat and completely cooled. Level should be the same both times

 

What O ring? Got a bit more detail?
The overflow works by allowing hot coolant somewhere to go as it expands and the radiator
cap reaches it's max pressure. When the engine cools it creates a vacuum effect and draws the coolant
back into the radiator lowering the level of the overflow. I'd say your system is working, although by the pics
it's overfull. It says right on it, Full - Hot. Full - Cold. Not a deal breaker, just something to follow.
Don't let it be dry. Always distilled water if used.

 

I would be more concerned about the color of the coolant. Is it mixed with something?

 

Looks like it was replaced with green antifreeze rather than the proper red (OAT?) product.


The level in my expansion tank responds in the same fashion you are experiencing (normal). I assume it's why they call it an expansion tank... although I have the proper red coolant in mine