have a 2000 mazda b3000 with 3.0l. Keep getting air pockets in coolant.

Tempature will spike sometimes, when air pocket purges, pushing coolant out of resovior, then returns to normal. Never does this unless truck is coming to operating temp.

Did not do this until i started to run heat?

Also notice it always pushes out brown coolant, from before i changed water pump. Also have coolant leak coming out from under front of intake manifold, can't see source of leak.

Replaced thermostat, radiator cap, and water pump. Thanx for any help, and forgive poor grammar.