Turbo Van overheating/air in system

Greetings,
I have been having trouble with air getting trapped in the cooling system of my stock 89 Turbo caravan. This last time I replaced the thermostat, I did not drill the hole in the thermostat, figuring I might get some hotter heat with the stock way of doing the thermostat.

I don't suspect the head gasket because the oil is clean and the antifreeze is clean, no white smoke and it runs well. However, I do notice some evidence of antifreeze leaks. The little bypass valve for the heater core has a tiny leak, and the rubber hose connecting the cooling line from the turbo to the thermostat housing (the one that is metal and once had a rubber hose crimped on) has a rubber hose with hose clamps. This rubber hose looks bulged and possibly leaky.

Question is, even if I replace these parts, will that 1/16" or 1/8" (can't remember size) hole in the thermostat solve the problem? Or should I be more concerned about why the air is getting into the system in the first place?
Thanks,
Lee

i would replace those parts.
the small leak when hot. will be an air vacuum when cooling off.
the cracks will allow air to seep back into the cooling system when you shut down.
causing the air in the system. a 180* thermostat is always nice for these cars. and you should always make sure they have a jiggle pin or a hole to bleed.

Normally drilling is not required. However it will make bleeding the air out easier. 1/16 or smaller is enough. Put the hole toward the top when thermostat is installed of course. Make sure your heater core is not restricted. That is the bypass flow for the cooling system. If after drilling the thermostat you still have problems you will need to check for things like head gasket leaking, cracked head etc.