So my car had started to overheat so i checked all the hoses turns out my heater control valve was faulty so i changed it car ran good, then started having the temperature fluctuate from normal to hot while driving and back and forth and when i parked the car the line going into the heater core was releasing steam and pressure so i bypassed the heater core and sent the upper radiator hose straight to the engine but car still ran hot, changed the thermostat and car still ran hot, my coolant level gets low fast and is fairly low but never compleely out also there is a hissing sound beneath the intake plenum? help dont want my motor to melt

 

Good chance that the hissing is where you are leaking coolant. Could also be many other things including a blown head gasket. Look for coolant puddles under your car, and for white smoke or steam out of the exhaust. Your motor won't melt, but it can break from overheating.

 

theres also fluid underneath the intake plenum in the bay area

 

No white smoke or steam or bublles in the coolant but am losing significant amount of coolant?

 

You said you were leaking some near the intake? I'd look to see if you can find a leak around there. Another way to find a leak is to run the car, park it, and put a piece of card board under neath and then check it a few hours later.

 

It seems to be under the intake Plenum but I cant spot it do any of the coolant lines run through there?

 

I dont know what engine your running, but assuming its a 80's SBC, you most likely have a stock steel or aftermarket aluminum intake manifold. There are water jackets that pass though your manifold. 4 of your bolts (IIRC) also run thru those passages, and if are not sealed correctly will leak. Dry it all off, warm it up and shut it off. CHeck for coolant in the small valleys on the intake, just below your valve covers. If you find coolant Id find the leaky bolts and re torque the manifold back to spec. Be aware that a leaky thermostat housing or upper radiator hose or even that hose you rerouted could be leaking from its base and causing this problem.

 

Its a 305 tpi all stock and that's exactly where there is always liquid in that little valley but could it cause my car to overheat and lose that much coolant

 

With coolant laying in the valleys of the intake manifold, first make sure it isn't coming from the water neck and working it's way back. Some of the intake manifold bolts go into the rocker valley, not a water jacket, so if they were "leaking" it would be oil. It is possible for coolant to push up around the intake bolts, but that would then mean you have a leaking intake manifold gasket, which you might.

 

where is the water neck located?