in line fuel filter suggestion bet tank and pump

[merrill]

I remember reading a thread about possible placing a high volume fuel filter (marine) in line between the fuel tank and the pump.

does anyone remember this thread or the recommendation.
I am supposed to pick up new fuel lines tomorrow and I may be re installing my fuel tank this weekend.  so I would rather put one in while I am re installing all the items.

thanks
matt

[Raymond]

I don't remember the thread you reference, but the size of our stock fuel filters is enormous compared to some new cars.  My fuel pump delivers a litre in under 15 seconds after the filter.  How much volume do you need?

Ray
'68 280SL 4-spd Coupe

[A Dalton]

Originally posted by Raymond

I don't remember the thread you reference, but the size of our stock fuel filters is enormous compared to some new cars.  My fuel pump delivers a litre in under 15 seconds after the filter.  How much volume do you need?

 Ray.
 I believe he is referring to using a large volume flow fiter on the suction side of the pump so that the pump is assured enough flow as to not cut down on the 1 ltr/15 secs  capacity after the main filter. This is usually done when one has a rusty tank problem to strain the gas one more time before it gets to the pump, even though there is the tank screen....if one has a good clean tank, the tank screen should suffice.....
A small/low volume filter on this side of the pump would restrict the capacity on the pressure side.

[merrill]

A dalton,
yes, you are correct,  I was referring to placing a filter between the fuel tank and the pump to keep debris out of the pump and fuel system.

the topic of placing a pump in this location was tied to a fuel tank or fuel system problem thread.  I did a couple of searches but did not find the thead.

matt

[Mike]

I have a fuel pump in the place that you are describing.  There was a filter there when I got the car but it was metal and you could not see through it.  It got clogged up.  That was  before I got my tank relined.  I replaced it with a clear "universal" looking filter from the local auto parts store and have had no problems but I am not sure this is a generally recognized solution or not.

Michael L. Hund

[ja17]

Hello,

If you add an additional fuel filter, be sure it is designed for a fuel injected engine.  If you use a standard fuel filter it may not be rated for the higher pressure or volume of the injected engines. I would hate to see it burst and start a fire.
There are many suitable filters out there, including in line Mercedes filters for later injected cars. The 1973 Mercedes 450SL uses a nice in line fuel filter with clamp on ends, but will run you about thirty bucks. A Datsun 280Z in line fuel filter is economical and designed for fuel injection systems and will cost around $7.00.

Joe Alexander
Blacklick, Ohio

[George Des]

The stock system has at least three fuel filtering devices. The screen in the tank, one on the fuel feed pump inlet fitting and another right before the fuel goes to the injector pump. If all are intact and are clean, I believe this is sufficient as intended by the factory. All that being said, I have disassembled many fuel feed pumps that are missing the inlet screen. This can cause problems by allowing small particles not filtered out by the fuel tank screen to get into the vane area of the fuel feed pump and cause scoring of both the vane and the vane contact surfaces ultimately leading to a noisy pump and worse yet some loss in pressure. This is even a bigger problem on the older style pump since the main shaft seal depends upon a very thin layer of clean fuel between the seal bearing surface and the pump body sealing surface to prevent fuel from getting into the motor portion of the pump. Again if all three screesn are in place it shouldn't be a problem. However, if the inlet screen is missing--you'll only know by taking off the inlet fitting--I'd recommend an in line filter between the tank and fuel feed pump. This is pretty much a gravity feed between the tank and pump, so high pressure should not be too much of a concern. On the other hand, you want to make sure that the in line filter does not overly restrict the flow between tank and pump.

George Des

[ja17]

Hello George,

You're correct in that placing the filter before the electric fuel pump puts it on the low pressure side and pressure should not be an issue. However these filters must be designed for high volumes of fuel since unused fuel in the W113 system, continually circulates through the filter.

Joe Alexander
Blacklick, Ohio

[George Des]

Joe, I agree. Unless you have an in line filter that allows a large volume of fuel through it, you could cause a fuel starvation problem with the in line filter. The screen on the fuel feed pump inlet, as you know, is just that--a screen and it will only restrict fuel moving through it if it has some substantial amount of junk caught up in it, so whatever in line filter put on should allow at least as much fuel to flow through as this screen allows. How you would find that out I guess would be by trial and error. My preference would be to avoid the in line filter and try to ensure everything else is in place. If you're missing the fuel feed pump screen, salvage one off an old pump. If the reason for considering an in line filter is a dirty tank, have it cleaned out.

George Des

[A Dalton]

I agree w/GD..
 If you have to add another filter when the system already has 3 , you have a dirty tank problem and the only remedy is to clean/change the tank.
  I think you will also find that with the gravity feed line from the tank to pump being the largest line of the system, that a  filter with inlet/outlet nipples that large should have enough flow requirements by design....if you so desire to use one.