c15 consuming oil

Sure its not leaking out anywhere or slobbering out the blowby vent?

 

Do you Check it every day? I would not add any but continue checking it to make sure it doesn’t get too low on the stick

 

The shrinking he's talking about is from the motor sitting at night. It's not a seasonal thing. When the motor is running.. it expands as it gets hot. When it's off. Everything shrinks.

Kind of like your coolant level. It goes up and down.

Everything expands with heat. Contracts with cold.

You might check your exhaust for Grey smoke when you start it up. Hard to tell in the cold. But if a slight oil leak drips in to the pistons. That will cause brief smoke from the oil burn..

Mine does that.

 

oil leaks past the valves or valve seals.. I'd imagine possibly turbo too. Could be a number of things.
Depending on year motor you got.
I could say what happened on a 99 I once drove. That thing was 3 gallons a day till it got fixed. And only had 200k miles. But you already rebuilt

@AModelCat would know more.