I'm sure we have been here before, and there is only one pump, so there must be some method of "balancing" between the two side of the saddle. 

On 28/01/2025 at 21:34, J.R. said:

Of course it can, it will have a feed pipe going from the LHS to the pump on the RHS with a valve that closes when there is no suction resistance, the opposite to the safety valve on a butane/propane cylinder regulator.

 

There is no seperate pump, please enlighten me on this venturi system that you speak of.

Here perhaps?

 

https://mbworld.org/forums/e-class-w211/734301-fuel-not-being-used-one-saddle.html

 

Plenty of info on the topic of saddle tanks if you ask Google.

 

https://letmegooglethat.com/?q=How+does+a+saddle+type+fuel+tank+work

 

 

Thanks Ernie, I can see it now from the diagram, I think the diagram is incorrectly drawn though as it does not show the return fuel circulating through the venturi loop in the LH saddle but going directly to the RH saddle via component 6.

 

Now I am questioning whether my Yeti actually has a second level sensor on the LH saddle, did I recall seeing a cover plate? I cant remember, VCDS shows the fuel volume on both sides but that could be an estimated figure, did it show the resistance readings for both sensors? Again I cant recall.

 

Every day is a learning day, there is so much clever stuff within our vehicles often hidden away that we are unaware of.

I think I need to play the lottery, finally some of the **** I talk actually turns out to be somewhat correct 🤣

16 hours ago, KiNeL said:

Plenty of info on the topic of saddle tanks if you ask Google.

Now where is the fun in that?

 

9 hours ago, J.R. said:

Now I am questioning whether my Yeti actually has a second level sensor on the LH saddle, did I recall seeing a cover plate? I cant remember, VCDS shows the fuel volume on both sides but that could be an estimated figure, did it show the resistance readings for both sensors? Again I cant recall.

 

By the looks of it, the pump is in one side and the sender is in the other EDIT - scratch that, you can clearly see a sender on the fuel pump as well, I guess if you have a lid and wiring on both sides it might have 2 senders

 

Edited 30 January, 20251 yr by SuperbTWM

Fuel flow from the LH side of the tank to the RH side is accomplished by a venturi effect system using fuel flow from the pump in the RH side of the tank.  Without checking somewhere I can't remember if it is supply or return flow that is used as the driving flow.  Hence the in-tank pump for 4x4 versions differs from the pumps for 2WD cars.   

 

I don't think there is a level sensor in the LH side of the tank and fuel transfer to the RH side is likely the reason for the slow drop of the fuel gauge from full in 4x4 cars. 

I've had a better look and there's nothing like a diagram:

 

Item 26 - This is the fuel delivery unit and sender for the fuel gauge in the LH side of the tank.

 

Item 27 - This is the fuel delivery unit and sender unit for the fuel gauge in the RH side of the tank

 

Item 32 - This is the pump for a diesel heater if fitted.

 

The level sensors must both have an input into the fuel gauge, perhaps averaging the left and right readings.   I would surmise that item 26 is not a transfer pump but a recirculation pump.  It is driven by fuel delivered to it by the pump in the RH side of the tank and after, passing through the venturi, this fuel "exhausts" into the LH side of the tank.   Meanwhile the venturi sucks fuel from the LH side and delivers it to the RH side of the tank.  Hence there is continuous movement of fuel between left and right sides of the tank.   

 

 

4 hours ago, bryetian said:

I don't think there is a level sensor in the LH side of the tank

 

There is, you can read its resistance and the fuel quantity in litres using VCDS.

 

3 hours ago, bryetian said:

The level sensors must both have an input into the fuel gauge, perhaps averaging the left and right readings. 

 

Correct, as above you can view the individual volumes making up the displayed fuel gauge reading.

3 hours ago, bryetian said:

 I would surmise that item 26 is not a transfer pump but a recirculation pump.

 

Item 26 is the LH tank fuel level sensor, the two pipes are the return line from the high pressure diesel pump via the filter housing going into the venturi in the float gauge which draws in fuel from the LH saddle and returns it to the RH tank with the returned fuel from the engine.

 

The diagram does not show a pick up pipe to the bottom of the tank well but it must have one.

 

Thanks for the diagram, I wont have to lift the carpet now to satisfy my curiosity.

 

On 30/01/2025 at 22:32, SuperbTWM said:

finally some of the **** I talk actually turns out to be somewhat correct

 

I'm jealous! 🤣