The water is drawing up through the lower.l opened the lower petcock valve and water is pumping out.When l opened the upper, its dry.Could it be an airlock or shot thermostat?

hhhmmmm hard question

change your thermostat is the engine running hot? also your manifolds could be blocked
is the engine fresh water cooled or is it a closed system if its a closed system the manifolds should be good

By lower pitcock, l am assuming u r talking about in the engine block. By upper pitcock, l am assuming you're talking about in the exhaust manifold.???????????????????????

When the water is pumped into the engine by the outdrive impellar pump, it goes through a hose to the thermostat housing. On the thermostat housing there should be three small hoses & one large hose. The other two small hoses go to the exhaust manifolds. Even if the thermostat is stuck shut, water should still be going to the exhaust manifolds. If it was an air lock situation, opening the pitcock would cure that & let the water flow.

SOOOOOOOOOOOO, the problem is obstruction somewhere. Remove the hoses going to the exhaust manifolds & see if the holes in the thermostat housing or manifolds r clogged with corrosion. If they are, u should also remove ur exhaust riser elbows to see if they r clogged also. If the riser elbows r clogged, they need to be replaced. If the thermostat housing is clogged, it needs cleaned out or replaced & if the small water inlets r clogged on the manifolds, then the rest of the water jackets in the manifolds r probably clogged as well, but try cleaning them out before replacing the manifolds.

Clogged exhaust riser elbows is the number one cause of engine overheating in inboard/outboard motors , but that does not stop water from getting into the water jackets of the manifolds.

Obviously you have a broken or worn impeller, which is located in the lower unit of your outdrive, These are usually made of rubber or plastic and should be replaced abopuit every two years, If you fail to get water to the upper part( engine) the motor will overheat ,stall, and eventually seize