Is fuel bubbling normal

[Rusty Karz]

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?

[chrs1961815]

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?

[Rusty Karz]

No additives. Should I be?

[chrs1961815]

Originally Posted by Rusty Karz

No additives. Should I be?

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

[Rusty Karz]

I use regular gas.

[1crosscut]

Sponsored Links (Register now to hide all advertisements)

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.

[Rusty Karz]

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

[Curtis in MA]

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

[Bruce_MO]

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

[Will N]

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.

[eagle]

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.

[Rusty Karz]

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

[Rusty Karz]

Thermometer would be handy. Getting one next time.

[midgetracer]

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

[Fhane]

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

[Kurt in NJ]

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

[HD Rider]

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

[Rusty Karz]

Only fuel available here is 10% ethanol.

[Rusty Karz]

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.

[Rusty Karz]

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.

[Patrick L.]

If its not vapor locking I wouldn't worry about it. Will it start up after sitting for a half-hour or so ?

[BRENT in 10-uh-C]

I am not so sure we are being 100% accurate in our comments above. To begin with, ethanol has a boiling point of just a tad under 175° (-not 147) and gasoline itself has a boiling point of about 200°, ...and more to the point is unless someone is running E85 fuel, there is only 10% ethanol fuel mixed in gasoline. Therefore that amount of ethanol is not that big of a deal when 90% of it is gasolene.


Second, folks get all 'excited' about underhood temps claiming it affects ethanol fuels, ---and while it can, most tend to overlook a riding lawnmower in the middle of July cutting tall grass. The stagnate underhood temps of that lawnmower likely exceed what we encounter with a Model-A, and yet we never hear of lawnmowers having percolation issues. My vote is there is an issue outside of the fuel itself that is creating the problem(s).


.

[Ernie Vitucci]

Good Morning all...Here in the southwest, many of us run Marvel Mystery Oil in our fuel. It has been around for many years and most hardware and auto parts stores carry it. It takes four ounces in 20 gallons or 2 ounces in 10 gallons to lubricate valve stems and to help stabilize fuel in hot weather. Good Stuff and not expensive. I use it in our 31 Model A and our 49 Packard and they both like it. Ernie in Arizona

[oldforder]

I also use MMO in the gas on all my classic cars. But I do mix it as recommended on the bottle, which is 4 0z per 10 gallons.

[katy]

My vote is there is an issue outside of the fuel itself that is creating the problem(s).

The OP was only asking if there was a problem, not that he had one.

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?

[Rusty Karz]

Sponsored Links (Register now to hide all advertisements)

A dose of upper lube sounds like a good idea. I will start using it in the Ford and also my MG. I learn new things all the time here.

[DHZIEMAN]

Originally Posted by Rusty Karz

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?

Well, your observation could be a problem! Has this plastic fuel filter been installed for a long time or is it new?
How warm is the plastic filter? If the plastic filter is not hot, I would venture the bubbling has something to do with fuel flow from the tank or back from the carb! Not sure, but if the fuel filter is not warm or you can put your hand around it and it is just warm, the fuel in it certainly is not boiling! It may be bubbling because of fuel flow with air in it but????? As a test, I would suggest removing the inline filter, replace with a piece of copper tubing the same size and see if the bubbling moves to OEM glass sediment bowl. If it does still bubble, provide some feedback either way to those following this post.

[30 Closed Cab PU]

Originally Posted by Rusty Karz

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.

If you bought an inexpensive IR Temp gun, be aware it may not work by going nuts when the motor is on. Inexpensive ones are sensitive to the Model As electrical noise generated by ignition/sparking. In extreme cases the gun is damaged.

[Rusty Karz]

Originally Posted by DHZIEMAN

Well, your observation could be a problem! Has this plastic fuel filter been installed for a long time or is it new?
How warm is the plastic filter? If the plastic filter is not hot, I would venture the bubbling has something to do with fuel flow from the tank or back from the carb! Not sure, but if the fuel filter is not warm or you can put your hand around it and it is just warm, the fuel in it certainly is not boiling! It may be bubbling because of fuel flow with air in it but????? As a test, I would suggest removing the inline filter, replace with a piece of copper tubing the same size and see if the bubbling moves to OEM glass sediment bowl. If it does still bubble, provide some feedback either way to those following this post.

This car does not have a glass sediment bowl. That is why I used the plastic filter. I felt like some kind of filter was probably needed and that was handy.

[Rusty Karz]

Originally Posted by 30 Closed Cab PU

If you bought an inexpensive IR Temp gun, be aware it may not work by going nuts when the motor is on. Inexpensive ones are sensitive to the Model As electrical noise generated by ignition/sparking. In extreme cases the gun is damaged.

Good to know. I bought the $26.00 one at Harbor Freight. Should read close enough for what I need but I will have the engine shut down before using it. Thanks for the heads up.

[30 Closed Cab PU]

Other tips.
Best to do it in the shade or in the garage in low light, the led pointer is very difficult to see in high light situations.
You can check accuracy by bringing water in a pan to a good boil, measure the water, should be around 212 F, dependent on what altitude you are.
Another nice measurement is after driving for a while measure the brake hubs, if one is warmer/hotter than the others, it might be dragging, or possible bearing issue.
With Motor running measure each radiator tube in a horizibnal line across the radiator. If one or more are quite a bit cooler, you have a blockage. Repeat at different heights on the radiator.
Measure the radiator inlet neck and outlet neck to see the coolant differential.
Measure the head on the head at the base of the spark plugs, all should be close
Measure the Block horizontally across on the driver side, if one area is a lot hotter possible rust scale in a water jacket (typically cylinder 4).


Record your readings, gives you a reference for future troubleshooting.
All kinds of fun things to measure.

[barnstuf]

Rusty Karz states the vehicle is a 1931 Tudor but he does not give us the insight of whether it is an early 1931 which would have a firewall sediment bowl or a late 1931 which would have the fuel line feed into an iron sediment bowl screwed into the carburetor. If it is the late 1931 perhaps there is no filter at the carburetor, and the in line filter is a substitute and is the cause of the problem. Cause of the problem or not it is a fire hazard.

[SSsssteamer]

Originally Posted by Patrick L.

If its not vapor locking I wouldn't worry about it. Will it start up after sitting for a half-hour or so ?

Ditto.
I remember the Christmas bubbling lights that had a little vial containing an alcohol mixture warmed over its light bulb. It didn't take much heat to make it the liquid bubble. Your fuel line is showing the same results. Go to steel lines and it won't bother you, because you won't be able to see the bubbling.

[DHZIEMAN]

Originally Posted by barnstuf

Rusty Karz states the vehicle is a 1931 Tudor but he does not give us the insight of whether it is an early 1931 which would have a firewall sediment bowl or a late 1931 which would have the fuel line feed into an iron sediment bowl screwed into the carburetor. If it is the late 1931 perhaps there is no filter at the carburetor, and the in line filter is a substitute and is the cause of the problem. Cause of the problem or not it is a fire hazard.

According to his response to me, the car has no sediment bowl! Following his other comments, it does have a fuel turn off! I thought all Model A's had a sediment bowl!

[katy]

This car does not have a glass sediment bowl.

Does it have the cast iron one? Or non at all? A picture of your setup would help.

[maako]

I have shut down my car before and heard boiling coming from the carb but it never seems to stop it from running.

[SSsssteamer]

The late '31 Model A with the fuel shut off on the engine side of the firewall should have it's cast iron sediment bowl correctly attached to the carburetor. It is unique.