2018 f150 3.5 boost

for some reason I’m losing coolant. No leaks can be seen and no fluid in floor.
however if I fill to minimum when cold, it will lose about an inch in the bottle overnight.
any ideas? Thanks

 

Have you checked your oil to make sure it isn't leaking into the engine? If so it would like milky indicating coolant in the oil.
Also I've read of turbos leaking and sometimes the hot engine parts evaporate/burn it off so sometimes it isn't visible.

 

Lots of ways these can burn coolant but losing overnight is weird. Maybe a collapsed hose opening back up and increasing system volume? An inch in the bottle is about a pint and if it were leaking that fast you'd know it.

 

would a pressure test show this?

 

Get a borescope and check (in this order):
1. Water pump
2. Heater hoses (inlet and outlet).Crimps often split and the Y-connections often leak.
3. The crimped fitting at the end of the crossover pipe. Find a PS3 connector at the bottom right side (looking from the front of the truck) of the radiator. You'll see a hose that turns 90 deg right after the connector. Check for split crimp.
4. Turbos (O-rings may fail)
5. Transmission cooling lines (crimped connectors)

These are the most common "not too bad" cases. I wouldn't think too much about not seeing a puddle under the truck, and just check the above items.

The reason I mentioned borescope is that often you can't see a leak because it's at the bottom of a hose/connector. With a borescope you can see up, and in hard to reach areas.

You may also want to consider leaking heater core (consistent with not seeing a puddle). Then there are always more unpleasant possibilities: head gasket, crack in the block, etc. Check your oil right after you shut the truck down, as someone mentioned before.