Dies while idling and losing fuel from the fuel bowl

[VooDoo]

So I'm in the process of trying to get my 1937 75 series convertible all dialed in so that I have no worries hopping in and driving it long distance. That's why I have a multitude of questions out there today. The furthest I've driven the car is about a 30 minute drive one ways. One thing I noticed, but after leaving the car idling for an extended period of time may be 15 minutes or so after the drive, the fuel bowl, loses fuel, and the bowl shows air bubbles coming in. The car starts to sputter and even if I try and give it a little gas it dies. I found this out today I was trying to leave the car running for an extended period of time because I was having an overheating issue that I was trying to diagnose as well. Any ideas what it could be? When I'm driving it, it seems to drive fine never losing any power or anything like that but again I haven't driven it for longer than about 30 minutes .  As you can kind of make out in the picture, the fuel bowl is not full and air bubbles are coming  up.

[James Landi]

Sounds as if the increase in engine rpms above idle creates enough pump strokes and vacuum from the fuel pump to over come what is likely a tiny pin hole or leak in the fuel line outside of the tank, or a fuel line pin hole in the steel tank fuel pick up,or an air leak in one of the fuel connection fittings on the pick-up side of the fuel pump, or even a small hole or tear in the fuel pump diaphragm, or perhaps a leaky gasket on the fuel bowl. Tracking down and finding the air leak will require a good deal of patience;however, I suggect that you start with what YOU may have done with the fuel system prior to experiencing this issue.  Perhaps you had fittings off, or the fuelbowl removed or you moved a fuel line under the car, or you dropped the fuel tank to make a repair. There are ways to test the fuel pump by supplying the pump with an alternate fuel source, but this involves safely managing gasoline, temporary flexible fuel hoses, hose clamps, etc. Be extra cautious if you feel confident in doing this work and have a fire extinguisher handy.   hope this helps, James 

[VooDoo]

Sounds as if the increase in engine rpms above idle creates enough pump strokes and vacuum from the fuel pump to over come what is likely a tiny pin hole or leak in the fuel line outside of the tank, or a fuel line pin hole in the steel tank fuel pick up,or an air leak in one of the fuel connection fittings on the pick-up side of the fuel pump, or even a small hole or tear in the fuel pump diaphragm, or perhaps a leaky gasket on the fuel bowl. Tracking down and finding the air leak will require a good deal of patience;however, I suggect that you start with what YOU may have done with the fuel system prior to experiencing this issue.  Perhaps you had fittings off, or the fuelbowl removed or you moved a fuel line under the car, or you dropped the fuel tank to make a repair. There are ways to test the fuel pump by supplying the pump with an alternate fuel source, but this involves safely managing gasoline, temporary flexible fuel hoses, hose clamps, etc. Be extra cautious if you feel confident in doing this work and have a fire extinguisher handy.   hope this helps, James 

I haven't actually done anything to the fuel system since I've had it. So that's gonna be a tough one

[signart]

Was the car beginning to overheat when the fuel problem occurred?

[VooDoo]

Was the car beginning to overheat when the fuel problem occurred?

It got slightly above normal. Please see attached picture of temperature reading. I do know now that it was about a gallon of antifreeze low because of one of the other issues I was having with fluid coming out of the overflow. Hopefully I saw that now by adding a small little rubber gasket to make sure the plunger is seated properly. You can see my other thread.

[signart]

Gauge temp looks ok. Not saying this is what happened here, but those cars are known to vapor lock when running hot or in hot weather conditions, which usually results in stalling, but will not immediately restart. Do well to research this for future reference.
Make sure you are not running coolant/antifreeze that is undiluted, no more than 50/50. Straight water will have a lower boiling point undiluted.
Good luck, I'm sure you will find plenty of help from experts on the Cadillac of your era.

As always, show a picture of your car when you get a chance, would love to see it.

[VooDoo]

Gauge temp looks ok. Not saying this is what happened here, but those cars are known to vapor lock when running hot or in hot weather conditions, which usually results in stalling, but will not immediately restart. Do well to research this for future reference.
Make sure you are not running coolant/antifreeze that is undiluted, no more than 50/50. Straight water will have a lower boiling point undiluted.
Good luck, I'm sure you will find plenty of help from experts on the Cadillac of your era.

As always, show a picture of your car when you get a chance, would love to see it.

I've read that the antifreeze actually has a higher boiling point than water so I was under the impression that antifreeze would be better than filling it up with water?

And you are correct. It will not restart until it's cooled down.

Here's a link to my Instagram account where you can check out the car

https://instagram.com/voodoocaddy?igshid=YmMyMTA2M2Y=

[V63]

Water actually cools better. If you are using alcohol blended fuel that adds SIGNIFICANTLY to the problems. It hardens rubber parts (read : mechanical fuel pump). The original exhaust heated heated carburetor system, once great for Detroit freeeze boils off the fuel the other times.

[VooDoo]

Water actually cools better. If you are using alcohol blended fuel that adds SIGNIFICANTLY to the problems. It hardens rubber parts (read : mechanical fuel pump). The original exhaust heated heated carburetor system, once great for Detroit freeeze boils off the fuel the other times.

So, even though the boiling point is lower with water, it actually cools better and wouldn't cause an overheating issue even with the lower boiling point if I'm understanding that correctly? I do currently run a 50-50 mix.

[signart]

I think you may be addressing two different problems. An overheated engine doesn't guarantee  that it will result in an overheated fuel problem. As noted ethanol fuel can overheat and evaporate and cause a vapor lock which starves the engine, especially at idle. Again research vapor lock as to the causes and potential remedies, but also take the advice given concerning cracks, pin holes, fittings etc.

Great looking automobile, by the way. You can't hide in that baby!

[V63]

Water has the best cooling quality but any engine would be overheating once it boils. So 'coolant' helps by raising the boiling point but at the same time it reduces cooling efficiency. Also water has corrosive issues. So YES! Best keep antifreeze at a 50/50 blend. Also verify system is pressurizing.

[Jeff Rosansky CLC #28373]

A couple of things. I run a little Marvel's in the fuel. It supposedly raises the boiling point of the fuel.
A comment above mentions a pinhole in the fuel line. Pinholes won't really show up until they are really bad. I had that issue with our 55  what I did was undo the line at the tank and plug it. Then I put some mineral spirits in the line to fill it up. Then I blew pressurized air in the engine end. After a couple of minutes, there were a couple spots on the fuel line, especially under the clips.
Just a couple of thoughts.
Good luck.
Jeff R

[James Landi]

"A comment above mentions a pinhole in the fuel line. Pinholes won't really show up until they are really bad. I had that issue with our 55  what I did was undo the line at the tank and plug it. Then I put some mineral spirits in the line to fill it up. Then I blew pressurized air in the engine end. After a couple of minutes, there were a couple spots on the fuel line, especially under the clips."

As I mentioned above and Jeff puts an additional emphasis upon, these tiny pin holes will NOT drip because there's sufficient vacuum from the fuel pump, the hole is tiny, and, as he states above, the likely spot is under a retaining clamp.  Jeff's approach, putting pressure AFTER the fuel pump on back to the tank input has efficiency, thus providing sufficient pressure to reveal any leak. Regarding the "hard starting" when hot--- I,too, subscribe to Jeff's fuel mix with Marvel oil.(I use a pint whenever I get gas)  It works "wonders" for me, and over time, I am not anxious about a "hot start/hard start" scenario.  Hope this helps, James

[skinny_tom]

This sounds exactly like what was happening to my 65 when it was hot. The fuel is boiling in the lines from radiant heat when you're idling because there is insufficient airflow to keep the fuel lines cool. Newer fuels boil at a lower temperature than older fuels. (The Marvel Oil idea is a new on to me-- interesting) In my case it was that the PO had put the wrong fuel pump in the car and it couldn't move the volume necessary to prevent boiling. Just like in your case, I would watch the level of the fuel in the filter drop and eventually the engine would stall. Let it cool down (or throw some ice on it) and it ran great.

My solution was to install the correct pump. With the fuel return line to the tank, it is able to constantly circulate fuel and prevent it from boiling. Without a fuel return line, I would be looking to insulate or protect the fuel line from radiant heat (from the engine) since at idle your car will be moving very little fuel through the lines.

[Chopper1942]

Make sure that none of the steel lines are close to the exhaust system.  If any are, fabricate a metal heat shield (heavy aluminum foil, light aluminum or steel plate, or go to a junk yard and get a heat shield blanket off a late model car), and mount it between the exhaust and the fuel line.

Replace all your old rubber fuel lines. 

If you havn't replace the rubber fuel hoses and want to check them and the steel lines for pin holes,  connect a vacuum guage to the hose/line at the fuel tank and start the engine. Should be 15-18 in.Hg. If not, either pin holes or a weak fuel pummp. Remove the fuel inlet hose from the fuel pump and check the pump vacuum. Again, should be 15-18 in.Hg.  If not, your fuel pump is weak and needs replaced. If your fuel pump has a return line, the pump isn't moving the fuel through the system fast enough to keep it cool. Now, reconnect the inlet hose and remove the return line hose.  Connect a hose to the return line outlet and place the hose in a qt jar.  Have someone start the engine and see how much fuel is returning. It should fill a qt jar is around 30 seconds.  If it is barely returning fuel, the fuel can overheat in the lines and vaporize.  Needs a new pump.

Hope this helps.  Good Luck!

[V63]

I have made it a policy to block off the exhaust heating of the intake manifold. It does help with alcohol blended fuels. It's also nice the intake manifold paint does not burn off.

I have not tried it on early UPDRAFT carburetor system yet. Cynical, that It might be more sensitive.

[fishnjim]

Lots of ideas, but no one can diagnose unknown, unseen equipment over the internet as we say.

some elementary Chem E:
Ethylene glycol(EG), aka anti-freeze depresses freeze point(FP).  So a 50:50 mix is the lowest freezing mixture, but it's not an even proposition at all percentage dilutions, ie: eutectic mixture - more than you woudl expect from the two.   There's a chart you can look up that describes this.
When one adds EG to depress FP, it changes the heat capacity of the mixture as EG, like most organics, has a much lower heat capacity than water.   1 vs ~0.4 say.   Therefore, EG absorbs less heat per unit(per pass) than water.
Q or heat = mass*Heatcapacity*temperaturedifferential
That affects the heat transfer coefficient and lessens cooling capacity slightly, but you're modern system is designed to handle that.  {Rate, Q/t, is proportional to heat transfer coefficient for the same area and temperature difference.}  Some of the early cars(pre-war) used plain water and they switched to alcohol in the winter.  There's was always the chance of not reacting in time and freezing the block, so EG was developed.  Low boiling alcohol tends to evaporate out so constant replenishment also required.
The boiling point increase comes from the pressurized system, which also prevents boiling at the surface.   There is some elevation due to the mixture as EG has a higher BP (197C), but not as much as it depresses FP.   That's a "molar" property so depends on molecular weight not weight/amount. EG:H20 ~3:1.  BP increases with pressure.

[VooDoo]

Lots of ideas, but no one can diagnose unknown, unseen equipment over the internet as we say.

some elementary Chem E:
Ethylene glycol(EG), aka anti-freeze depresses freeze point(FP).  So a 50:50 mix is the lowest freezing mixture, but it's not an even proposition at all percentage dilutions, ie: eutectic mixture - more than you woudl expect from the two.  There's a chart you can look up that describes this.
When one adds EG to depress FP, it changes the heat capacity of the mixture as EG, like most organics, has a much lower heat capacity than water.  1 vs ~0.4 say.  Therefore, EG absorbs less heat per unit(per pass) than water.
Q or heat = mass*Heatcapacity*temperaturedifferential
That affects the heat transfer coefficient and lessens cooling capacity slightly, but you're modern system is designed to handle that.  {Rate, Q/t, is proportional to heat transfer coefficient for the same area and temperature difference.}  Some of the early cars(pre-war) used plain water and they switched to alcohol in the winter.  There's was always the chance of not reacting in time and freezing the block, so EG was developed.  Low boiling alcohol tends to evaporate out so constant replenishment also required.
The boiling point increase comes from the pressurized system, which also prevents boiling at the surface.  There is some elevation due to the mixture as EG has a higher BP (197C), but not as much as it depresses FP.  That's a "molar" property so depends on molecular weight not weight/amount. EG:H20 ~3:1.  BP increases with pressure.

So if I'm understanding correctly, antifreeze has a lower heat capacity than water. Therefore water would cool better. What I'm not quite grasping is the boiling point vs heat capacity. If antifreeze has a higher boiling point than water, I had assumed a 50-50 mix with cool better because it wouldn't get as hot as fast due to the higher boiling point? Will water cool better because there's no organics in it but yet boil and evaporate out quicker than antifreeze? If so, one would just need to continually check and add water to the radiator if using straight water in theory?  Thank you for the chemistry analysis. Now I just need to make sure I understand it.🤣

[Paul]

Andy, I had the same issue on my '59. The issue is Vapor Lock. The boiling point of fuel today is lower than it was back in the time your car was made. Therefore, you would want to install a fuel return line from the fuel bowl to the gas tank. When the engine heats up, it heats the fuel in the engine compartment and the fuel becomes a vapor, and therefore, isn't delivered to the carb, causing the engine to sputter and ultimately die out. The return line allows the fuel vapor to return to the tank and liquid fuel to flow thru to the carb.
You can install some heat shielding as an additional measure but it may not be enough to solve the issue alone. This was a common issue and was solved back in the 50's. You will see a lot of a/c Cadillac's have the fuel return line.
As far as coolant, if you live in the northern US, 50/50 will protect the engine year round and prevent it from freezing in the winter.
The issue you have with fuel is independent of the cooling system.

[VooDoo]

Andy, I had the same issue on my '59. The issue is Vapor Lock. The boiling point of fuel today is lower than it was back in the time your car was made. Therefore, you would want to install a fuel return line from the fuel bowl to the gas tank. When the engine heats up, it heats the fuel in the engine compartment and the fuel becomes a vapor, and therefore, isn't delivered to the carb, causing the engine to sputter and ultimately die out. The return line allows the fuel vapor to return to the tank and liquid fuel to flow thru to the carb.
You can install some heat shielding as an additional measure but it may not be enough to solve the issue alone. This was a common issue and was solved back in the 50's. You will see a lot of a/c Cadillac's have the fuel return line.
As far as coolant, if you live in the northern US, 50/50 will protect the engine year round and prevent it from freezing in the winter.
The issue you have with fuel is independent of the cooling system.

I've been trying to read up on the Vapor lock. Seems like a vapor filter as you mentioned with a return line back to the tank. Would solve this. The filter if I'm understanding it correctly should go on the carburetor side of the fuel pump, correct? I was trying to keep the engine bay as original as possible and didn't really want to see a filter where one shouldn't be, but if I'm going to drive this thing a lot, it shouldn't really matter. Driving reliability should. It's  by not getting Judged. Just driven a lot. Same reason I'm contemplating a
12 V conversion vs a 6v Alternator to replace my warn generator