Every two Months I loose 1.65 qts of oil but none to the ground. WHY? on 2002 Chevrolet Astro

I get my oil changed every 3 mo. I am loosing oil but nothing on the ground. What are the possibilities that it could be? I have 117,000 miles and the van is in otherwise great condition.

4 answers
How many miles are you driving in those two months? The oil is probably being burned by the engine. This is normal. You add oil as necessary.
Valve cover gasket(s) or other , leaking onto exhaust and burning off before it hits the ground? Any smoke on first start-up? How many miles in 3 mos.? Proper viscosity oil being used?
i would bring it to a shop that perform test to find out your oil leak and maybe compression test also.
any smoke from the exhaust? is the air filter oily?