5w30 Castrol oil loss

4 quarts low on a 1500 Chevy? That thing only holds 5 quarts and the low oil level light should come on at about 1.5 quarts less than max. Something not right with description.

At that mileage towing you are likely going to use some oil. I have an 05 Chevy 1/2 ton with 160k miles that will use about a quart between oil changes if most of the mileage is towing. Doesn't use a drop if not towing, started using oil towing around 130k.

Have you checked your coolant bottle to make sure it hasn't found its way there?

Pool wrote:
A message came up on the dash about low oil level. I checked and was 4 quarts low. I do not have a leak I looked all over. The truck has 139,000 miles on it and regular oil changes have been done. I use Castrol 5w30 as recommended. Where could the oil be going evaporation. This has not been happening between every oil change.

Not a good sign, how many miles on the change? Does it consume oil normally? If so at what rate.
If the consumption is inconsistent, have you been towing more on this current change, idling more.
What about internal leaks, rings, valve seals, should produce blue smoke but not always.