What is making this sound?

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67fish383S

67fish383S

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I'm a noob, so I apologize if this is a silly question...Today I took my new-to-me '67 Barracuda FB FS 383 4 speed for our longest drive yet on one of the hottest days so far (90+), and when I got back, it was making this weird hissing, sizzling sound under the hood. I captured it as best I could with my phone:


I could not see any liquid being ejected anywhere on the hot block. It almost sounded like fuel boiling in the carb. I opened the air cleaner and nothing looked amiss and the sound didn't change. It subsided after a couple of minutes. Was she jut pissed at me for driving her on a stupid hot day?
 
I couldnt see if you had AC or not?
Almost sounded like the AC stabilizing.
Def sounds like a liquid pressuring off internally.
If upper radiator hose was stiff, maybe antifreeze pressuring off somewhere in water pump or past the thermostat area.
How was your dash temp reading?
 
Joey4speed said:
I couldnt see if you had AC or not?
Almost sounded like the AC stabilizing.
Def sounds like a liquid pressuring off internally.
If upper radiator hose was stiff, maybe antifreeze pressuring off somewhere in water pump or past the thermostat area.
How was your dash temp reading?
Click to expand...
No AC. Temp was normal during the drive. Coolant coming out of the overflow was the first thing I looked for. Never experienced a noise like that with no obvious cause. It sounded external, but I couldn't see anything. Thanks
 
Get a piece of gas line hose or the like, stick it up to your ear and find out where the source is.
 
Dennis,
My 383 made similar sounds before it overflowed. I suspect your antifreeze was past the boiling point. Remember, water boils at 212°, but the radiator cap compresses that so it actually can get above that temp before the spring under the cap allows it to overflow.
Sometimes my big block wouldnt overflow until I shut it down, when the water stopped circulating and the fan stops cooling it would build up enough heat (pressure making sounds) to eventually overcome the spring in the radiator cap. Then I would later see a small puddle beneath the drip tube.
Make sense?
After it cools, check your level in the radiator. If you can see antifreeze, your good.
I always squeeze the upper radiator hose first, if you feel pressure in that hose, dont open the cap, its the same pressure in the upper radiator tank.
Joe
 
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I heard that same noise with my 318 one time. Come to find out, there was not enough sealer on the exhaust stud that penetrates the water jacket and the water/steam was leaking from the stud at the corner of the exhaust manifold where the stud was allowing a little coolant to escape. Not saying this is your problem, I don't know about big block bolts/studs contacted the water jacket in the heads or block.
 
Long tube funnel makes a good stethoscope/listening devise.
 
So it happened again. This is the second time. The common factors between the two events are that the weather was stupidly hot/humid, and I had just returned from a somewhat lengthy drive. I had just turned the engine off, and I immediately heard a gurgling from under the hood.

This time I was able to (somewhat) see the source of the noise. Holy crap, engine fire waiting to happen. I say I could somewhat see the source because I could not positively identify where the fuel was coming from - the carb or the mounting gasket or both.

You can sort of see what I mean in the following two videos. You have to look closely to see the fuel bubbling and gurgling at/near the base of the carb:



It only lasted for a minute or two and seemed to subside proportionally to a drop in temp. I let it cool for a few more minutes and removed the air cleaner and started it up (fire extinguisher at the ready). I wanted to see if it was leaking, and if so from where. I say "if it was leaking", because I swear it seems like it's not a leak. Rather it seems like the fuel is boiling out of the carb somehow. Remember, this has only happened when the weather has been unusually hot. Or at least it has only revealed itself in that situation.

This third video is during that experiment:


No leaking, bubbling, gurgling, nothing. The only weird thing was the backfire that happened when I exercised the throttle a bit. But no fuel ejected anywhere. And this was probably max ten minutes after the initial event.

I really hope someone has some ideas about how this is happening. It has been years since I've driven a carbureted vehicle, and I've never owned a 4bbl. It is a Carter AVS. My instinct is to pull the carb and rebuild it, but I'd really like to understand how/why this is happening. Would a rebuilt carb do the same thing on a stupidly hot day? Should I concentrate on lowering the temp under the hood instead?

Obviously I'm not going to drive it again until I get this figured out. Any and all suggestions/theories would be welcomed. Thanks
 
Well there you have it, it seems the float valve is not shutting off.
additionally, judging by the burned off paint at the choke-well,Ima guessing, your heat crossover is not working, or is majorly full of carbon, or the Heat-Riser valve is frozen, or the exhaust is restricted.
The latter may be the principle cause of the former, but may not be the whole of it..

Yes it is possible for the fuel to boil in the float bowl and bubble over into the throttle bores. The lightest gas molecules start to boil at 95*F. Your first defense against that is an insulating gasket between the carb and intake.
If you have an IR gun, shoot the carb in several places,next to the intake, and also shoot the chokewell, looking for the highest temps.
The only way to clean out the heat crossover is to remove the intake, flip it over, remove the rivets holding the splash shield on, and chisel out the crud. Then chisel out the actual crossover as well.
Your engine craves cold air from somewhere else than under the hood. Underhood air could be two or three,or more, times as hot as what is hitting the rad.
 
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AJ/FormS said:
Well there you have it, it seems the float valve is not shutting off.
additionally, judging by the burned off paint at the choke-well,Ima guessing, your heat crossover is not working, or is majorly full of carbon, or the Heat-Riser valve is frozen, or the exhaust is restricted.
The latter may be the principle cause of the former, but may not be the whole of it..

Yes it is possible for the fuel to boil in the float bowl and bubble over into the throttle bores. The lightest gas molecules start to boil at 95*F. Your first defense against that is an insulating gasket between the carb and intake.
If you have an IR gun, shoot the carb in several places,next to the intake, and also shoot the chokewell, looking for the highest temps.
The only way to clean out the heat crossover is to remove the intake, flip it over, remove the rivets holding the splash shield on, and chisel out the crud. Then chisel out the actual crossover as well.
Your engine craves cold air from somewhere else than under the hood. Underhood air could be two or three,or more, times as hot as what is hitting the rad.
Click to expand...
Thanks for all of the helpful info. Sounds like I have some work to do. Incidentally, the previous owner said the heat riser is new. I will pull the carb and intake and have a look at the crossover. Insulating gasket sounds like a good idea. I was surprised to see how thin the existing gasket looks. I'll also look at ways to duct cool air into the carb. It has a reproduction original air cleaner, and I hate to mess with that, but all my driving will be in the summer, so cool air probably overrides originality.
 
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An IR gun is cheaper than pulling the intake off, and will help diagnose if it even needs to be done. Some paint just won't take that heat....... so I could be wrong.

To check the exhaust, the engine needs to be working hard. What I do is braze a ft long length of brakeline into the exhaust pipe, on the engine side of the muffler. Then route a low-pressure gauge up to where you can see it from the driver's seat, and finally, take it for a workout.
Ideally the pressure should not exceed 2psi. If your system hits more than 4psi you want to find and fix the problem.
 
I would think that raw fuel hitting a hot intake manifold must have smelled like a gas station, no?
 
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