After doing my heater and having these issues what i did was
1 ditch the shut off by pass loop. now the oil cooler line goes straight to my heater core and from the heater core to the oil cooler.. i use to have some tees and shut off valves for a winter/summer mode.
2 i bought a little 5/8 water pump from amazon for 20$ and wired it to my blower motor power. when you turn the blower motor on the pump turn on. this pump helped with the air pockets. if forced the water through fast enough to burp the heater.. i get a lot more heat out of the core now. i also had to insulate the duct work from the core to the cab. that also makes a hug difference
1 ditch the shut off by pass loop. now the oil cooler line goes straight to my heater core and from the heater core to the oil cooler.. i use to have some tees and shut off valves for a winter/summer mode.
2 i bought a little 5/8 water pump from amazon for 20$ and wired it to my blower motor power. when you turn the blower motor on the pump turn on. this pump helped with the air pockets. if forced the water through fast enough to burp the heater.. i get a lot more heat out of the core now. i also had to insulate the duct work from the core to the cab. that also makes a hug difference