coolant low with no noticeable leak

[AnotherOldJeepGuy]

Helping someone with their 2005 Toyota Tundra that was overheating.  Checked the overflow tank and it was all but empty so filled it up a bit over full actually, started it up and it was running at a normal temperature, fluid ended up right around the full mark.  That was yesterday, this morning it was nearly empty again.  We put some paper under the truck overnight and it was completely untouched.  Topped off the radiator itself and the OF tank now waiting again.

 

My question is, if you don't see any leak and don't smell anything, where is the fluid going?

[Pete M]

if it was low enough, it might have sucked fluid in as it cooled. 

[AnotherOldJeepGuy]

Gotcha.  What would have caused it to get low in the first place since I don't see any leaks?

[derf]

Could be a leak that only shows itself at operating temperature.  Could be a head gasket leaking into a cylinder.

 

What does the oil look like?  If it has the look of a milkshake, that's where the coolant is going.

[AnotherOldJeepGuy]

I'll take a look at the oil and see.