Coolant leak from filler neck
 

lack of pressure in your system can cause overheating..
seal that...

Man, that sucks.

That pipe is press fit into the housing and held in place with epoxy. If it's loose enough to pull out, you may be able to remove it, dry and clean everything, hit stuff up with JB Weld, and re-install. But I don't know if I would trust that since it's a pressurized system - if it doesn't hold that pipe will pop straight up and shoot coolant out.

Best move would be to get a new water pump housing. It's a fair amount of work to replace but not terrible, you could do it in an afternoon. Get a new water pump to housing gasket and a new water pump housing to engine gasket, that should be the only soft parts you need. May also want to go ahead and get a new thermostat and any coolant lines that connect to it that look sketchy. Also may be worth getting a new water pump if you're in there.

Dale

Drain the system, clean and dry the area, and jb weld or epoxy it back in place like Dale suggested or remove it completely and tap for a npt nipple. For single turbo cars I remove those nipples all the time and seal them with aluminum npt plugs and epoxy.

If it were me, I'd follow IRP's advice and tap the hole to replace with an NPT nipple - we do that often on race cars. Pressed-in fittings can blow out due to thermal expansion, etc.

Yeah, you would have to do something for the nipple on the rear iron - cap it off somehow.

On a stock-ish car I'd either replace the whole housing or drill/tap and put in a nipple of some kind. You can probably find a brass 90 deg. nipple that would screw in to an NPT hole and you could put the hose on. But, you really should pull the housing or something so you don't load up the cooling system with drill shavings, and if you're already pulling it to do the work might as well just replace with a good used one.

Eliminating the line on a near-stock car would also require fooling with the throttle body to remove the thermowax and all that business. I don't know if it would be worth going that far down the rabbit hole.

Dale

Yes. I pull the nipple out of the rear iron as well and tap it for a npt plug. Best way I found was to cut the nipple off near flush, then use a reverse drill bit. If you do it correctly the bit will grab the nipple and pull it right out.

One method that WORKS but isn't sexy is a short piece of hose with a bolt stuck in it and 2 clamps. Looks dumb but I'll be damned if it doesn't hold. Good thing it it doesn't require a lot of skill, properly drilling, tapping, and plugging like Ihor described isn't an easy task and can become more of a problem than you started with.

Rubber caps will ALWAYS fail. I've seen people trying to use vacuum caps or whatever, they aren't rated for the pressure and will fail in short order.

I've also run a coolant hose from the rear iron to the above-pictured nipple, just modified a stock hose to fit properly. Just as long as the hose isn't pinched or rubbing against something you're fine.

Dale