Petrol Cock

[John Clarke]

Hi all
Just browsing an old registry topic via Google search and the various thoughts on using the Petrol Cock or leaving it well alone.
I Brimmed the gas tank prior to leaving for the Le Mans 24hr trip and checked the gas tap, I usually leave it in the 'AUF' position but stupidly exercised the tap to the 'ZU' and the 'RES' position and immediately spelt gas. Sure enough there was gas seeping out of the shaft . Put a tissue under it and noted how much was escaping and put the tap back to the 'AUF' position and the leak has stopped ! The car is fully loaded for the trip and I don't want to drain the tank and have the cock apart now.
Not sure what to do. Any comments gratefully received.
Regards Jay

[Wes Bender]

I hesitate to offer advice, considering the hazards involved in fuel leaks. If you don't have time to remove and rebuild it, you might consider leaving it in the AUF position and proceeding. Just be extra cautious in your watching/smelling for a petrol leak. Bear in mind that, should it start leaking in the AUF position, you'll be in worse shape than you are now.

Sorry, but there just isn't really a good answer. My conscience tells me that you really should either replace it or repair it before departing.

[Geoff Fleming]

The fuel cock serves several important functions. If parked on an extreme slope, fuel can enter an engine cylinder and fill it,( more likely if a carb check valve is faulty), thereby causing hydro-lock, so it is best to turn the fuel fully off.
The fuel cock also can prevent a thief from driving more than a very short distance before the engine stalls...few modern thieves know about such devices. The main purpose Porsche used them on the 356, was to let you know when the main tank was empty. You then selected the reserve and could make it to a filling station.
If the rod which attaches to the fuel cock is not aligned properly, it will put pressure on the valve and thereby leakage results. You have to line up the fuel cock carefully with the rod which is used to switch between the three positions. It is a pretty simple device but has to be maintained and 'exercised' by use. If the cork gasket is never bedded- in by usage it may leak in another position when finally used.
If the cock leaks in the RES position it negates the ability to utilize the reserve, so address the problem rather than not use that ability. Porsche did not design it to be left alone or they would not have bothered to install it.

[Hugo Karasawa]

Fuel leak during your road trip to Le Mans is something you do not want.
Remember Mr. Murphy.
Better repair or replace that fuel cock.

[Mike Smith]

John,

If you do not want to fix it before going, at least buy a New Fuel Cock and take it with you with some method of draining the tank and PLENTY of rags to mop up any mess

[Harlan Halsey]

John,
My experience is those valves rarely just begin to leak spontaneously. They fail when you switch positions. The switch lever can momentarily tilt the rotator, or the seal can fail. My policy has been for years not to use the function. (That function is a carryover from the VW which had no gas gage.) So if it went back to AUF and is not leaking now, it is highly likely that it will just start leaking, but if it does it will be a slow seep.

The basic design of the fuel cock leaves little margin for varying gasket thickness, imperfections, or for varying spring force. And the gasket surface and the rotator surface have to be perfectly smooth and flat too. Cork varies widely in grain structure. At one time a friend and I tried making nylon gaskets, thinning the rotator to accommodate a thicker gasket, etc., just to see if the thing could be improved, but we gave that up because the design margin wasn't there. So back to just leaving the switch alone.

Geof is correct about the belt and suspenders function. Should the carb inlet valve leak, and the car be parked so that the tank has a pressure head, hydraulic lock is possible.

[Vic Skirmants]

I always use the fuel cock to turn off the gas. Constant use keeps it functioning in all positions.

[DonCichocki]

+1, what Vic said.

[Jon Schmid]

+2 on Vic's comment, except I have a hard time remembering to turn the gas back on again for the next outing! Under the right circumstances I also like to flip the petcock onto reserve for a few minutes to make sure no water has accumulated at the bottom of the tank. We're stuck with ethanol laden gas here in California so that is a concern. Knock on wood, neither of the petcocks in my cars leak.

[John Clarke]

Thanks everyone for the replies and suggestions. I know that I should refurbish or replace the Pet Cock. I'm really annoyed at myself for not checking this sooner, as I have had loads of time preparing the car and only discovered the problem after I filled the gas tank and moved the pet cock selector rod. As I mentioned the leak stopped when I returned it to the AUF position, so what I have done is put a coating of 'Heldite' gas and oil sealant round where the selector shaft enters the flange. And I will NOT move the selector rod till I return from Framce. I just hope Mr Murphy has not crept on board, (there isn't any room !)
Cheers Jay

[Geoff Fleming]

John,
I believe you will find that even Murphy is forgiving! Have a good trip.

[Norm Miller]

+2 on Vic's comment, except I have a hard time remembering to turn the gas back on again for the next outing!

Jon,
On my motorcycle, I have a sticker that helps.
"TURN THE GAS ON DUMMY.
Norm

[Harlan Halsey]

I was familiar with the fuel cock because I came to my first Porsche (1962 B) from VWs which didn't have a gas guage. For a while I turned it on and off, but then grew tired of playing with it and just left it in the AUF position. With the Convertible D, the valve began to seep and the rubber mat swelled a bit, hence the repair episode mentioned above. But this string has caused me to wonder, how do people use that valve?
Last Saturday our local Porsche club gathered to view a private car collection. These people drive their cars to the Breakfast most months, and go on one or two hundred mile tours two or three times a year. About two dozen cars showed up so I dedided to conduct an informal poll:

One or two people turn the valve off all the time.

One couple didn't know it existed. (New Owners)_

About five people leave the valve on all the time, citing leaks if you move it.

By far the largest number ues it only as a reserve. They rely on it, but actually use it only once in a blue moon. They never turn it off.

None of these cars had leaking valves Saturday.

[Bill Lawless]

I didn't used to turn mine off regular..... Until I got about a gallon of gas in the oil and ran the car for 20-30 seconds.. Faulty gas valves in carbs..
Now I always turn it off, like I do on my older BMW motorcycles...

-Bill

[Jon Schmid]

+2 on Vic's comment, except I have a hard time remembering to turn the gas back on again for the next outing!

Jon,
On my motorcycle, I have a sticker that helps.
"TURN THE GAS ON DUMMY.
Norm