Gas in the sump, HELP

[emf]

I have an interesting problem with my Model B engine. I first put a fuel pump on the car because my pair of Stromberg 81's seemed to be starving for fuel. Sure enough, the pump cured the problem. Some time later, I needed to change the oil and discovered the sump had about a quart too much oil, and it was very thin. I had gas in the oil. Thinking this must have come from a ruptured pump diaphragm, I had another core rebuilt and put that on. Now it is about 1 1/2 years since and it has happened again, about a quart over, contaminated with gas. It's hard for me to believe that this pump has the same issue, but how else can the gasoline get into the sump? Any ideas??


Frank

[BRENT in 10-uh-C]

Originally Posted by emf

I have an interesting problem with my Model B engine. I first put a fuel pump on the car because my pair of Stromberg 81's seemed to be starving for fuel. Sure enough, the pump cured the problem. Some time later, I needed to change the oil and discovered the sump had about a quart too much oil, and it was very thin. I had gas in the oil. Thinking this must have come from a ruptured pump diaphragm, I had another core rebuilt and put that on. Now it is about 1 1/2 years since and it has happened again, about a quart over, contaminated with gas. It's hard for me to believe that this pump has the same issue, but how else can the gasoline get into the sump? Any ideas??


Frank

Typically speaking, as soon as an engine comes up to temperature, gasoline inside of a crankcase with evaporate out of the oil. So if the oil level is truly up by 20%, then that quart of fuel being added did not come from the fuel leaking out of the carburetor(s) into the intake and into the cylinder(s). If so, then you would have likely experienced hydrolocking. You did not mention this, but I am assuming you are using a mechanical fuel pump?? If so, it is believable that you have a diaphragm that is leaking into the crankcase.

[rotorwrench]

In the early years of commercial aviation, it was common to use oil dilution in the winter. A measured amount of fuel was metered into a special hopper on the inside of the oil tank that mixed with the oil around the oil pump pickup so as to thin the oil for start up and warm up. Brent mentioned the evaporation process previously and this will actually happen rather quickly after warm up.

The model B fuel system was designed for pump feed from a rear mounted fuel tank. When you add the model B engine system to a car that has a gravity flow fuel system, there can always be a chance that a failed fuel pump will continue to leak into the engine block even after the engine is shut down. I would strongly advise to shut the fuel tank valve off when done with motoring for the day or even when parked for extended periods during the day. Some of the modern materials used in reproduction parts don't last well with modern fuels. Definitely seek the best sources for fuel system seals & diaphragms that can take the modern fuels.

[emf]

I usually shut off the gas under the dash, but sometimes forget. Both of these pumps were rebuilt with modern materials for today's gas. The first by Ken Isador and the second by Then and Now of Weymouth, Mass. Both are reputable rebuilders. I have an airtex style electric pump that I used for a while when I had trouble finding the correct mechanical pump. I may swap it back in to help diagnose the issue.


Frnak

[katy]

Try asking the pump rebuilders for their thoughts on this issue.

[Anteek29]

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Recently experienced the same issue. Fuel pump rebuilt with new diaphragm and all is well.

[nkaminar]

So what about blocking off the hole where the fuel pump mounts to the engine and installing an electric fuel pump. My electric fuel pump on my 1930 Fordor with a Weber carburetor is mounted inline with the fuel line that runs from the bottom of the tank to the sediment bowl on the firewall. It is just the right length to replace most of the straight section of the fuel line. It makes for a clean fuel line installation in the engine bay. I double clamped the hose connections to make sure that no leak developed inside the car.

[The Master Cylinder]

Originally Posted by nkaminar

So what about blocking off the hole where the fuel pump mounts to the engine and installing an electric fuel pump. My electric fuel pump on my 1930 Fordor with a Weber carburetor is mounted inline with the fuel line that runs from the bottom of the tank to the sediment bowl on the firewall. It is just the right length to replace most of the straight section of the fuel line. It makes for a clean fuel line installation in the engine bay. I double clamped the hose connections to make sure that no leak developed inside the car.

Do you have a picture of your setup? Sounds like the way to go.

[emf]

Originally Posted by The Master Cylinder

Do you have a picture of your setup? Sounds like the way to go.

As a matter of fact, I had an electric in the setup before I found the mechanical pumps. I may go back to it to test the theory. See photo above...



Frank

[nkaminar]

Here are photos. This is before I added second clamps. Magnetic cable clamps hold up the wires. No holes or glue.

[BRENT in 10-uh-C]

Originally Posted by nkaminar

So what about blocking off the hole where the fuel pump mounts to the engine and installing an electric fuel pump. My electric fuel pump on my 1930 Fordor with a Weber carburetor is mounted inline with the fuel line that runs from the bottom of the tank to the sediment bowl on the firewall. It is just the right length to replace most of the straight section of the fuel line. It makes for a clean fuel line installation in the engine bay. I double clamped the hose connections to make sure that no leak developed inside the car.

Also, isn't it noisy inside? Most electric fuel pumps are a tad noisy. I guess you could always isolate it up between the tank and the firewall and then plumb it in hard line.

Rubber fuel line inside of a passenger compartment, -especially when there is not any electrical interrupt in case of an accident or fire would not be something I would want to be around.

[rotorwrench]

I don't know if fuel pressure may be involved or not. A lot of the multi carb set ups run a pressure regulator just so it won't overpower the float valves.

[emf]

I also would be afraid of a pump setup inside the cabin, but he's not having trouble with his. I ordered a gauge and it will be here tomorrow, so I can report the pressure numbers then. The pump rebuilder went through the rebuild process with me and agreed with me on the remote likelyhood that two pumps would fail so soon in the same manner. He suggested I measure the fuel pressure also. Tomorrow when the gauge comes, I'm going to measure the pressure with both the mechanical pumps and the electric pump and report back. If a regulator is necessary, so be it...



Frank

[nkaminar]

The noise doesn't bother me and my car is a quiet as a mouse. That is because my hearing is gone. I just turn off my hearing aids when driving. I have to keep a lookout for the lights from emergency vehicles, but I have to do that even with the hearing aids on.

Yeah, fire in an accident is an issue, I agree. Otherwise I am OK with the safety aspects.

[emf]

I have done some testing and made changes, so here is the report...


I was able to measure the fuel pressure at the output of the mechanical pump and measured .8 psi. NOT MUCH! After giving it some thought, I would guess the pressure of the gravity system at the carburetor should be about .5 psi, given the height of the cowl tank and the height of the carburetor float. I decided to remove the mechanical pump entirely and see how things went. Still runs like a raped ape. I still think the pump should go back to the rebuilder, I'll see how far I get on that one....


Frank