smell gas in water

[v8quest]

let me tell you what its doing
had the car about 3 weeks now.about once a week,it wants to try and run hot...and the heater stops blowing heat.
last week,i changed the themostat..it was a 160 to a new 195.car ran all week long...most it has since we have had it.usually,it tries to act up every 3-4 days.Car ran with the hot hand never even getting close to half way
before i go on,it has a new radiator.
ok,car ran for one week,wife goes to buy groceris and comes back in and syas it is 3/4 way up..and heat stopped.i get in it...dive it..heater come son..hands goes down some.mostly stays at 3/4.i slow to stop..no heat..i go again..heat comes back.
soooo,i pull it in the yard...check everything...no gurgling of water...everything feels right.
check oil again..no mixing.
but i do take the radiator cap off.....smell it...smells like it has gas in it.I decide to take the vent plug off one more time. As soon as i do...i hear and see it burp 4 bubbles.
so,put the radiator and vent plug back on...tell the wife to give it a go...comes back in 5 minutes....temp hand is between cold and half way(perfect) and heater is working.
so,my questions
1)why the gas smell?
2)why trying to overheat/no heater?
would a small HG prick cause all of this.would thta make the bubbles in the water and the gas smell?

 

[MustangLX-5.0]

It's either one of 2 things.Either you got a head gasket leaking or there's a small crack in one of the cylinder heads near one of the intake valve guides.The latter would explain why you would be getting gas smell in your radiator and bubbles coming out the bleed tube.The bubbles could be creating hot spots on the cylinder heads while driving.Then then you are at idle,the low system pressure lets the excess bubbles float into the heater core which would explain the cold air at idle.You may also want to check the carpet on the passenger floor.Make sure there aren't any wet spots which would be a sign of the heater core leaking.And if the heater core were leaking in the right spot,it could introduce air into the cooling system.

A head gasket could also introduce plenty of intake or combustion gases into the cooling system.And it doesn't always mix oil with coolant.It just depends on where the gasket is leaking.Now,if you recently change the t-stat and radiator,make sure you properly bled all the air out of the cooling system.You might've just got the last bit of air out.

How is the level in the overflow reservoir? Does the exhaust smoke? How many miles?

 

[v8quest]

when i took the vent valve off...the bubble "burped" in the radiator.not in the vent valve.I had the radiator cap off and i watched them "burp".
I checked the floorboards..i also thought heatre core..no leak at all.all dry.
water level is fine....no smoke..and 113k miles

 

[MustangLX-5.0]

Probably just had excess air in the system.Try running the engine a little more,shut off and then pull the vent plug (never pull plug when engine is running).There still may be a little more air in the system.Now,if air keeps popping up in the system constantly then you got one of the above mentioned problems.So you shouldn't have to bleed the air more than 2 or 3 times.Keep a close eye on it for a little while and post if anything else comes up.