Fuel boiling?

[dmopar74]

I finally drove my car after 3 years of working on it and notice what looks like fuel bubbling in the fuel filter. It bubbles alot and continues after I shut the car off for a few minutes and then slowly stops, is this fuel boiling? I've never seen it before but I've only idled the car in the garage.

 

[dddDuster]

 

[RustyRatRod]

It could be but I doubt it. How is it running?

 

[Dicer]

Could be sucking air, somewhere between tank pickup tube and fuel pump.

 

[dmopar74]

Seems to run decent, I think it wouldn't be a bad idea to replace the fuel pump, this car sat for over 20 years and I think I smell some fuel in the oil

 

[413]

Did you change the oil? did it stay clean very long?

 

[dmopar74]

Yes fresh oil, it's still clean

 

[RustyRatRod]

I think the car is fine. It's perfectly normal for bubbles to occur in the fuel system. You have the line run a good ways away from manifold heat and the filter has plenty of room around it. If the fuel was boiling, the engine would run like a dried up turd.

 

[Dana67Dart]

Pure-gas.org

See if there is a station near you.

Next time the tank is low fill it up with alcohol free gas.

Then redo it a couple more times. Then check to see if you have bubbles in your filter.

No bubbles and it's the alcohol in the fuel causing your issue.

My car stock 273 2 bbl would bog down if the engine and compartment got hot like sitting in a fast food line.

Changed to alcohol free and I can't make it happen even on a 100 degree day

 

[Oldmanmopar]

Could be many reasons for bubbles but it could boiling point for the ethanol is much lower.

 

[MadScientistMat]

The stock fuel line routing can boil the fuel a little - if you don't have hot restart issues, it's not a problem. But you may want to switch to a metal fuel filter; plastic ones can turn brittle with heat.

A common mod to reduce fuel boiling is to run the fuel line up and over the valve cover instead of around the water pump.

 

[slantsixdan]

The mod MadScientistMat is described (parts and procedure) here.

Fuel pump: careful; new parts store items are garbage. More specifically, New \6 fuel pumps tend to be much poorer quality than we used to be able to get, and they've been coming through with much-too-strong diaphragm springs, giving 8psi fuel pressure — about double what it should be, which makes for all kinds of flooding problems. If you go too far the other direction, old fuel pumps pose risks as well—rubber doesn't react well to age, and some of it doesn't react well to alcohol in the fuel. There is no guarantee, but I had consistently fine results buying and using NOS AC № 6972 fuel pumps, even with ethanol in the gasoline. Cheap and easy on eBay, such as this. If you want to eliminate even that small gamble, you snag one of the bolt-together pumps, get a rebuild kit for it (making sure to specify a 3 to 5 PSI spring), toss the kit in the pump, and off you go.

 

[dadsbee]

Problem solved..

 

[dmopar74]

Well I replaced all the rubber fuel connections and hooked up the charcoal canister purge to the carb, it was blocked off. I haven't seen any more bubbles yet. I am leary of new part quality so I will stick with the current fuel pump unless I find a problem with it. I will get around to doing the fuel line mod one of these days

 

[Mattax]

It is fairly normal for some fuel to vaporize enroute to the carburetor.
Gasoline is made up of many components, and so portions of the fuel vaporize over a wide range of temperatures. Some portion will vaporize under 150*F and some won't vaporize until over 350*F. Winter fuel has a larger proportion that vaporizes at lower temperature. This aids in starting.

Chrysler addressed the vapor lock and hot restart issues in several ways.
1. Tilt the fuel filter so the vapor goes out the outlet. (1963).
2a. A small internal bleed in the fuel pump (circa 1972-3)
2b. An earlier (1960s) kit that creates a tiny vapor bypass around the fuel pump to address hot restart problems.
3. If really desprate, techs were advised to relocate the fuel filter before the pump for certain heat issues (knowing the tradeoff between hot restart and hot running issues . Moving the inline filter before the pump makes it harder for the pump and drops the fuel pressure in the line - which can induce vaporization)
All discussed in the 1972 Engine Performance Facts and Fixes. (MTSC ref book)

 

[Mattax]

I've never seen it before but I've only idled the car in the garage.

It will always be more prevalent when idling
1. Low consumption of fuel leaves fuel near the exhaust and engine longer.
2. Low air flow can mean less cooling in the engine bay.

 

[slantsixdan]

2b. An earlier (1960s) kit that creates a tiny vapor bypass around the fuel pump to address hot restart problems.

Yup, offered for Slant-6 Dodge trucks starting around 1968. Called a "Flood-Check kit", listed in the '63-'68 Dodge Truck FPC as "pressure bypass kit" (Psst, Mattax: that 14-73-3 you were tryna trace to a TSB number is just the part type code it's listed under). I think it was a PFR (purchase for resale) by Chrysler, also available in a variety of forms as an aftermarket problem-solver deal — a couple other models are shown here.

Kit is two brass fittings, one for splicing into the short rubber line on the fuel pump inlet, and the other for threading in between the fuel pump outlet and the line to the carb:

Tiny is right; both fittings had a side barb with a teeny pinhole at the end. Those side barbs were connected by a piece of plastic tubing (really bad material choice; the smart installer substitutes fuelproof Tygon). The boil-and-fizz action is visible in the return tube when the fuel is hot:

All discussed in the 1972 Engine Performance Facts and Fixes. (MTSC ref book)

Yup, and there's a downside to consider:

That is probably why the factory's next effort was the 3-nipple (vapour-bleedoff) fuel filter described in the fuel line mod post. It does a nice job alleviating overpressure in the pump-to-carb line less or none of the cold-start consequences of the earlier solutions. Plus, with the line from the 3rd fuel filter nipple going way back to a colder part of the fuel system, instead of to right before the fuel pump inlet, this method doesn't feed heated fuel back into the hottest part of the system.

 

[Killer6]

Great, but really keep track of fuel possibly being in the oil, being 'upside-down', the Slanty can have a leaky diaphram that puts fuel in the crankcase w/o any coming out of the breather hole.

 

[Mattax]

Thanks Dan. The flood package I have is in a blue and white box and the Chrysler part number is also on instruction sheet. And yes the original hose has mostly disintegrated. Otherwise the same as the one you show. Tuner wrote "That was the authorized Mopar cure for the Long Ram 413 Chrysler 300 letter cars with air conditioning. The Long Ram had extra exhaust activity in heat riser pluming near the fuel pump to heat the manifold plenum under the carbs." I haven't tried to verify this, but I suspect its like the older parts manager who rattled the p/n off the top of his head. That's how I first heard about it.

 

[slantsixdan]

@Mattax your inbox is full

 

[rays266]

STOP IT! My 3rd A body slant 6. Boiling gas on all 3. Such an easy fix. Insulate the carb from the intake manifold with the thick base gasket. I place the new gasket on top of the old usually crushed gasket. It's that easy. Problem solved here 3 times. 3 linkage disconnects, maybe your fuel line. Happy motoring, no more rough idle when hot. If you need the gasket, hit me up here.

 

[slantsixdan]

STOP IT!

Who should stop what? I'm guessing your order is aimed at…uh…everyone giving advice that differs from yours, then, is it? Asking for a friend with enough experience on this question on this kind of engine to know that the thick carb base gasket/insulator needs to be there, yes, but often isn't enough to prevent or solve this problem on its own, no.

place the new gasket on top of the old usually crushed gasket

…thus making an air leak much more likely because leaving the old crushed gasket in place, and screwin' up the choke and kickdown operation because carburetor now too high. Mmm…no, thanks; I'm drivin'.

Sorry, that was unnecessarily wordy. I mean: STOP IT!

(and after you've STOPPED IT!, you might want to take a hard look at your pics, find the spring you've put in the wrong place, and put it back where it's supposed to be.)

 

[rays266]

lighten up. It is worked for me three times my kit down linkage works fine. I’m not getting any errors for the base. Every single thing is fine and it starts.

 

[RustyRatRod]

STOP IT! My 3rd A body slant 6. Boiling gas on all 3. Such an easy fix. Insulate the carb from the intake manifold with the thick base gasket. I place the new gasket on top of the old usually crushed gasket. It's that easy. Problem solved here 3 times. 3 linkage disconnects, maybe your fuel line. Happy motoring, no more rough idle when hot. If you need the gasket, hit me up here.

View attachment 1716416521

View attachment 1716416522

Ummmm.....what?

 

[rays266]

Who should stop what? I'm guessing your order is aimed at…uh…everyone giving advice that differs from yours, then, is it? Asking for a friend with enough experience on this question on this kind of engine to know that the thick carb base gasket/insulator needs to be there, yes, but often isn't enough to prevent or solve this problem on its own, no.


…thus making an air leak much more likely because leaving the old crushed gasket in place, and screwin' up the choke and kickdown operation because carburetor now too high. Mmm…no, thanks; I'm drivin'.

Sorry, that was unnecessarily wordy. I mean: STOP IT!

(and after you've STOPPED IT!, you might want to take a hard look at your pics, find the spring you've put in the wrong place, and put it back where it's supposed to be.)