Is my Expansion Tank Cap supposed to "Hiss"
 

I Had just got back from advance auto and shut the truck off and popped the hood.
I could hear a quiet little "hissing" near the cap, not a real loud quick hiss but a soft slow one
anyway ive had head gasket work done and still im adding coolant often.
wondering if i should replace the cap or is this normal?

Quit driving it, you have been around long enough to know that your engine is in trouble again.
If you had a shop do the gaskets, take it back tomorrow, if you did them, well what can I say but go buy all new bolts and gaskets again.

It will only do that if the cap is bad or it is over pressurized.

And since he is going thru lots of coolant, something was missed on that job.

I was just going out to do an oil change, Disco Mike... I should prolly wait on that now, huh?

i hate to say this but if i need to open it back up again, im thinkin about having the dealership do this job, they quoted me the same price as the "mechanic" that did that job.
theyre ten minutes away as opposed to 2 hours at least.

How much did they quote you?

1200.00 or 1400.00 i have it somewhere

I got a similar problem. I am pretty sure it is the head gasket if you are loosing coolant, it isn't leaking and the cooling system is over pressurizing.

But why pay double? If the indie didn't do it right he should redo it, right?