When is empty really empty on a W210?
 

I have driven mine until the light comes on, then till the needle is at the bottom edge of the light and then when filled only been able to put 17+/- gallons of fuel in the tank. What have other folks found?

I've run our gasser out of gas. It has the "miles remaining" countdown in the dash and it was quite accurate. I've never run the '99 diesel out of fuel, but I've been real low. I'm pretty sure I forced in 21.7 gals with maximum topping off.

The fuel gage appears very accurate on both our W210 cars. When the needle is centered on the white line (below the warning light), you're in trouble ;)

The fuel tank is metric which converts out to 21.1 US gal (80 litres). Out of that 2.6gal. is considered the reserve (when your needle hits the red or white margin on your gauge).
I have pressed my luck once or twice and ran it almost on air but only was able to squeeze 19.8 gal into it. Its tough because of the foaming of the fuel especially with winter diesel. I get the most complete fills when the current car sits nose down at an angle....it seems to allow the trapped air in the foam to move out the neck easier and allow more tank volume for fuel. On some of my diesels it was the opposite.....nose up/ tail down vented air out better.
Truefully...I try to not allow the tank to drop bellow the 1/4 mark. Priming and restarting the thing out on a busy highway is not in my future...I've done that before...not fun! Plus you stand a chance of sucking water/ wet fuel out of near empty tank.

I routinely put in 19 to 20.5 gals in mine. I check my mpg's every tank and watch the trip meter closely.

My reserve light seems to come on a "bit" early, I'm guessing somewhere around 17.5 gals remaining.

On mine, if the needle were to go beyond the lighted area you'd be SOL.

First question is what is "full"? Is it when the pump clicks off? If so then you probably are at least a gallon under filled since diesel foams quite a bit and if you are patient you can squeeze more fuel into it.

I'd say if you fill to the neck with liquid and are only getting 17 gallons into it from the point where the needle is at 0 then the gauge or sender is off. Typically if I drove it to 0, which I have done, I would put around 20 gallons in. I always fill to where liquid (not foam) is at the neck, usually about a gallon past the point where the pump clicks-off automatically. I typically fill when the reserve light comes on, and put a little over 18 gallons in.

Even if your gauge is off I would not fret...if you have a little extra in the tank you'll be assured of not running out without having to think about it.

Isn't the water/wet fuel always sitting at the bottom of the tank ?

That was my impression.

HUH? I don't understand this statement.

If you mean why does the pump click off before it is full it is because the foam will actuate the pump's auto-stop feature long before the liquid fuel reaches the neck.

I think he is talking about F18's post about water in the tank.

I've squeezed 20 gallons in the tank. Gotta be patient as the fuel foams, then goes down. Top off then go down again. I tilt the nozzle so that the fuel is flowing down directly on the fuel neck, I think it slightly reduces the foaming potential.

210 fuel
 

The fuel tank holds 60 litres from empty,when i ordered my car from new i spec it with an optional 80 litre tank.

I always thought they were all 80 liter tanks...if you read the owner's manual I believe that is the stated capacity. It is definitely NOT 60 liters.

The other thing about stated capacity is that there is no such thing as "exact" as they have to add some air space for both expansion and the filler neck. It is possible to get more than 80 liters (20.6 gallons) into the tank therefore from completely empty. I know I have pumped 20.6 into mine during one fill up and the gauge was above 0 and the car was still running so I have to assume it still had some fuel in there.

Mine is a 65 litre tank.

The most I've had out of it is 500 imperial miles, there was about 0.5 litres left in the tank :)

Perhaps they changed it in '98 or these were US spec tanks but I am fairly certain my owner's manual calls the tank 80 Liters. I don't have the car here at the moment or I'd confirm this.

I'm pretty sure mine said 80 liters also.