Fuel Filter

Note: In cars with the fuel filter located below the fuel tank under the car, replacement is easier if the fuel tank is empty. Try to schedule fuel filter replacement when the tank is nearly empty.

Only the Super Beetles have the fuel filter at the tank outlet. Standard Beetles had a mesh screen INSIDE the tank - long, like a pencil.

Note: John Connolly (Aircooled.Net) wrote to say that he has seen Super Beetles with a filter inside the tank.

To get to the fuel filter in a Standard Bug, you must first remove the fuel tank. Then you remove the outlet fitting from the bottom of the tank, and the long, round, pencil-like filter comes out.

The Standard Beetle also has a filter inside the fuel pump if it's the older, original style (upright, raectangular shaped pump). The later model, which has a lower profile to clear the larger diameter of the alternator, has no built-in filter.

If the pump filter is the original type, the filter is behind a nut (about 13mm I think) on the side of the pump, just in front of the fan belt as it passes the pump body. This belt gets in the way a bit as you undo the filter plug. The filter is a fine plastic gauze. If the pump has no nut in this position, you have the other type of pump without the filter.

A clogged fuel filter is easy to spot when you know what to look for. If the filter is clogged it will usually be full of fuel, rather than almost empty as it is normally. The VW filters have the outlet deep inside the paper cone, so when they are new the fuel moves through the bottom of the paper and straight into the outlet -- thus filter is almost empty. As the paper gets blocked the fuel progressively climbs higher to find fresh paper, so a full filter is a blocked one.

Note:It is very easy to install the fuel filter backwards. There is usually an arrow on the filter, indicating the direction the fuel is supposed to flow through the filter. If the filter is installed backwards means you won't be able to see it clog up - the clogging will occur inside the paper cone rather than outside, where it's visible. Dave reports that having the filter installed backwards affected the operation of his Super Beetle - it stumbled on acceleration just as it would if the filter were clogged.

It's rather odd to see ANY stuff in the filter, except if the tank is rusty. If the tank filter shows a lot of rusty flakes, it usually means there is rust inside the fuel tank, and the tank will need to be cleaned. See our Fuel Tank Removal and Refurbishment procedure for instructions on how to clean the tank.

Rob describes a problem with his Bug that really had him going for a while. He wrote - I'm usually quite good at diagnosing problems with VW Beetles, but this one had me flummoxed for a while.

My Bug is a '68 semi-auto, converted to manual, with '71 1600cc dual port engine. I have a 30PICT/3 carburetor and a single vacuum distributor. The car still has its solid '68 engine lid -- no slots. I'll be installing slotted lid before winter in Australia ends). I bought this car about 5-6 weeks ago, from a PO who shouldn't be let loose anywhere near VWs, though he's had them or years.

The problem appeared to be fuel delivery. It exhibited the following symptoms: The car ran for about 5-6 miles before the fuel stopped flowing -- the float bowl and fuel filter emptied out. The fuel filter was between the fuel pump and carburetor, so I could see if the pump was delivering fuel. I waited for five minutes or so, then cranked for a while, and the fuel started flowing (visible in the filter) and the car started. All was well for another 5-6 miles (a lot longer than a single float bowl full of fuel).

This problem happened just a few times after I first bought the car (before I replaced the perished fuel lines), then it stopped. Later the problem started again, this time worse.

Here's some history -- the car had a PO who ignored his VW ownership responsibilities, so soon after I bought the car I did the following -

• Replaced all rubber fuel lines (perished badly and weeping).
• Removed and cleaned the tank screen.
• Cleaned the tank (no crud appearing in the filter any more).
• Replaced the fuel pump with a known working one.
• Fully stripped and cleaned the 30PICT/2 carburetor (I've had this carburetor on my other '70 Bug for 30 years and know it inside and out).
• Checked the float needle valve (it's definitely not sticking).
• Replaced the fuel filter.

So -

• The problem occurred with the fuel cap on or off, so it wasn't a tank vent problem.
• Fuel flowed freely out of the pipe under the tank.
• Fuel flowed freely out of the rear end of the steel body line -- there was no blockage there.
• Fuel flowed freely into the carburetor under gravity flow.
• All rubber lines were clamped -- there was no possibility of air entry or fuel weeping.

I wondered if the fuel pump had something stuck under one of the two small valves inside which might be reducing flow (from the perished rubber fuel lines or crud from the tank), but replacing the pump produced no change at all.

I wondered about the fuel pump overheating (vapour lock), so tried pouring cold water on it after the problem occurred. This seemed to help (a few bubbles sometimes appeared in the upstream filter), but only occasionally, and the pump was only warm to touch. The problem was the same when I replaced the pump -- no change. The steel fuel line around the left side of the engine was not hot -- it got only warm to the touch.

When this problem was occuring it was winter in Australia, so the temperature was between 3-6C (37-43F) at night, and under 20C (68F) during the day. Engine heat did not appear to be a problem.

In his typical fashion, Rob resolved this problem himself. The answer turned out to be the most simple thing -- the $3 fuel filter!

He wrote - The filter looked okay, and I could easily blow backwards though it. The thing was apparently partially blocked, enough so that only a trickle of fuel could get through. So giving it a rest allowed what was in the pump to leak through and partly fill the bowl, then as I drove, the trickle was less than the fuel use and eventually the car conked out again.

Can you say "Doh!?"

I thought I was following my own philosophy - look for the simple things first, but I didn't think simple enough in this case. When the "blow through it" test worked on the filter, I didn't consider it again until I spoke to a mechanic friend. The car ran home that night (from the shop where I replaced the filter) and to work this morning, without missing a beat.

Who'd a thunk it!

An additional fuel filter between the fuel pump and the carburetor was an add-on that was considered a good idea by some, a not so good idea by others.

John Connolly(Aircooled.Net) wrote regarding the filter between the fuel pump and the carburetor -

Dave posed the following question to Rob - What do you think about the fuel filter between the fuel pump and the carburetor? John Connolly recommends that there shouldn't be one there, others think it's a good idea. What's your opinion?

Rob responded - John's main concern about putting a filter there seems to be that the weight of the filter may put additional strain on the brass inlet spigot in the top of the carburetor -- a known source of fires in VWs. Mine worked loose about two years ago, and I "knurled" the section which is pushed into the carburetor so it can't work loose again. The other concern I've seen is that if that filter got clogged, the pressure from the fuel pump might cause the fuel line to pop off the filter and spray fuel all over.

Both arguments have some merit, but they are not overiding considerations. If your carburetor inlet is firm, the filter is not likely to pull on it much, and you can always arrange the filter so the weight doesn't pull on that spigot. And the fuel pressure is only 2-3 psi, so it doesn't take much to seal the fuel lines against that pressure, so even a blocked filter would not cause it to pop off. The fuel pump design allows for this - the operating lever simply doesn't descend to touch the cam drive until fuel is used, so if the filter got blocked, the pump won't pump anyway.

If you had only one filter, I'd say put it before the pump, either in the engine bay or under the tank, but with two filters, one under the fuel tank and one between the fuel pump and the carburetor should be fine if you're careful to make sure the latter fuel filter won't pop off.