As title says, i've noticed last winter in cold temps (below freezing) that the fuel gauge doesn't go down below 1/2 tank. I've almost ran the gas tank dry because of it once. Problem disappeared in the summer but we have gotten our first bout of freezing temps and the problem is back again. Does anyone have an idea of what the problem may be? 2008 GL320 CDI.

 

There are two fuel pumps on the diesels, one on each side of the fuel tank (see parts diagram items 20 and 30.)




Each pump has a sending unit mounted to it which is basically an arm with a foam float attached. What I've seen in the past is that one of the arms is stuck in the up position and fools the computer into thinking that there is fuel in the tank since the computer takes the average of the two sending units to indicate the fuel level on the gauge. The computation happens (typically) inside of the instrument cluster. I'd pull the pumps and ensure that the sending unit arms are free and not bound to something, and if that isn't the problem, then you're likely facing an issue with the instrument cluster.

Looking at the diagram (I've never done this on a GL, but have many times on other similar designs), this is a typical setup. Once you access the pumps (under the carpet which will require rear seat removal) there is a large plastic ring that is holding the pump in place. You take a large screwdriver and a hammer and carefully set the screwdriver against the ribs on the plastic ring, and strike it (counter clockwise) with the hammer to loosen the ring. Then lift the ring out of the way and you can pull the pump. When reinstalling, be careful to ensure that the rubber gasket that holds the pump in place is in the correct position (note this before you pull the pump out to begin with), or you'll get a fuel leak and smell vapor inside the vehicle.

 

Very good post. Will try to pull the pumps when I have a chance, probably next oil change.

 

If they freeze in cold weather it could be the floats but it also could be water in tank. Before pulling anything off dump some diesel fuel treatment (one that removes water) and let it slosh in there for couple days. If it doesn't help- pull the floats and observe.

 

Thx alx. Been above freezing last few days so needle started working right again. I bought a case of Diesel 911 and will use it a few fillups and see the results next time temps drop again.

 

Hi. I had same issue on my Gl 320 cdi. I'd like to know that for solving this problem, should I change the fuel pump or just sensors? and if I should sensors how can I find?

 

I've been using Diesel 911 and havent had the issue since then.

 

you should start by reading and trying out my suggestion in this thread?