[T3] Breather cap

Jim Adney jadney at vwtype3.org
Sat Aug 26 14:01:33 PDT 2017


On 26 Aug 2017 at 9:50, William J wrote:

>  What about the fuel pressure regulator ?  I've only seen drawings of one 
> showing what's inside . It has a metal disc and a sort of machined end bore 
> and the spring pressure against the disc is the actual adjustment when you 
> turn the adjustment screw increasing /decreasing the pressure on the 
> disc/valve . From what I can tell not ever cutting one open the fuel port on 
> the side connected to the pressure side of the ring seems sealed from the 
> spring area and one side of the disc other wise fuel would find it's way out 
> the adjustment screw. What I don't know is when the system is shut down  is 
> if the disc closes all fuel flow to the return . If it does then it could 
> bleed off the pressure.

It's certainly possible for the regulator to be the leak, but in general, they 
don't. The seal is a metal to metal seal between very nicely polished 
surfaces. If water got in there and rusted something, that could cause the 
problem.

A "fix" that Bosch came up with for the big Mercedes V-8 D-jet cars was to 
drill an extra hole in the regulator so it would bleed down instantly. This 
forced boiling to push gas forward in the fuel ring, rather than backward. 
This meant that there was fuel closer to the engine, next time you tried to 
start. I've never tried this solution, as it would be hard to implement, but it 
has always seemed intriguing.

>  Also reading the post on worn pump brushes and dirt and or water finding 
> it's way into the tank because the over flow hose is cracked . Wouldn't even 
> rust caused by ethanol based fuel because it absorbs water since these old 
> systems closed venting is by now shot cause the pump brushes to fail . There 
> is a filter before the pump some of this crap rust , dirt has to be trapped 
> by the filter or are we talking very tiny particals the filter cannot stop.

The internet is full of ethanol haters who will grab at any symptom and blame 
it on ethanol. You won't have a water or rust problem unless excess water 
gets in your gas tank. This can happen if you drive with your gas cap off, if 
you drive in the rain with a cracked overflow hose, or if you happen to buy 
gas at a station that has a bunch of water in its gas.

The latter is extremely rare, but it can happen. Even if that happens, it won't 
cause a rust problem unless that water/gas is left in the tank for an extended 
period, months or years. In normal use it gets mixed up with the gas and is 
pumped thru the engine harmlessly. A larger bubble of water might cause a 
momentary burp and loss of power, but then it's gone.  

By far, the most common water problem in our fuel systems is due to the 
overflow hose, which has always cracked by now. When these cars were 
newish, I typically had to replace them every 2-4 years. The OE hose just 
didn't last very long. I've drained as much as a half gallon of water out of the 
gas tank of a type 3 that had been driven in the rain with a cracked overflow 
hose, until that brought it to a stop. (Water is more dense than gas, so the 
water collects at the bottom of the tank, where the gas pickup goes.)

The Bosch filter has a paper element which captures water, making it hard 
for gas to get thru. This can cause a problem if there's lots of water, but if 
there's just a bit of water, and ethanol in the gas, the water gets dissolved in 
the alcohol and passes. I don't think the filter paper is particularly fine, so my 
guess is that the dirt in some areas contains particles that are fine enough to 
pass thru and still be abrasive enough to stick in the copper and eat away 
the brushes.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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