Is fuel bubbling normal
 

I have a 31 Tudor. I notice that the fuel in the little plastic fuel filter I have on it seems to bubble as if boiling when I shut the engine off after driving. The carb is pretty warm but does not seem excessively so. Is this normal or does it indicate a problem?

Re: Is fuel bubbling normal
 

I would say that it is probably boiling. I can't really think of any other reason why it would be. Do you use any additives in your fuel?

Re: Is fuel bubbling normal
 

No additives. Should I be?

Re: Is fuel bubbling normal
 

No I was just thinking if it could be something chemical. Do you use regular gas?

Re: Is fuel bubbling normal
 

I use regular gas.

Re: Is fuel bubbling normal
 

Rusty if your gas tank doesn't have excessive rust/debris and you have a pencil filter in you don't need the plastic filter.

Re: Is fuel bubbling normal
 

Tank has been cleaned and treated. Not sure if I have a pencil filter. Don't recall seeing one.

Re: Is fuel bubbling normal
 

How long does it do it?
If you have a pin hole as it cools it might suck air in.

Re: Is fuel bubbling normal
 

If the filter is a long way from the carb, I can't see how it's boiling. Even if it's close, I would guess it's simply air bubbles as the fuel drains a bit down to the carb as it's shut off. Check its temp with your hand or a cheap infrared temp indicator from Harbor Freight. They're super handy. I just googled boiling temp of gasoline and it's 203 degrees F.


I have clear fuel lines on a '53 Ford flathead and I see a surprising amount of bubbles. If you don't have symptoms of fuel starvation (sputtering and missing at high speed), I'd say you're fine. Good luck

Re: Is fuel bubbling normal
 

IMO, the sediment bowl that is already in the system is enough to deal with what you'll experience with a clean and sealed tank. Adding an inline filter will just impede fuel flow in a gravity fed system.

Re: Is fuel bubbling normal
 

If you are getting excessive heat, yes gas will boil at somewhere around 200+ degrees F, depends on the blend. If the timing is incorrect, then there will be excessive heat. If all is running fine, just some boiling in the line at shutoff, it won't hurt anything. If its really a hot day 200 degree engine bay in ok.

Re: Is fuel bubbling normal
 

It stops when I shut the tank valve off. Sorry I did not think about it until just now

Re: Is fuel bubbling normal
 

Thermometer would be handy. Getting one next time.

Re: Is fuel bubbling normal
 

The initial BP of gasoline is about 95 degrees F. it is a mixture and the final BP is about 200F

Re: Is fuel bubbling normal
 

Plastic fuel filter. Sounds like a fire hazard to me. Should be a steel fuel line. No rubber no plastic.

Re: Is fuel bubbling normal
 

If you use the cast iron sediment bowl, and steel pipes you never have worries about fuel bubbling

Re: Is fuel bubbling normal
 

If you are using an ethanol blend, ethanol has a much lower boiling point. Something like 147*.

Re: Is fuel bubbling normal
 

Only fuel available here is 10% ethanol.

Re: Is fuel bubbling normal
 

Plastic filter is far from the manifolds but I'm probably going to get rid of it as I'm sure it is a weak link in the system.

Re: Is fuel bubbling normal
 

Thanks to all who replied. weather has turned bad here so I won't be taking it out for a while but I did buy the infrared thermometer and that should tell the tale if the engine is over heating. This car is an ongoing project and I'm glad you guys are here to ask for help.