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Draining Diesel Fuel Tank

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7.1K views 2 replies 2 participants last post by  Jim-ML320W164  
#1 ·
I have a '07 ML320 CDI that was accidently filled with gas. The engine was never started, and It's been towed to my house. I've disconnected the fuel line just before the fuel filter, and have attempted to suction the fuel line from there with a generic fuel pump. I wasn't getting much success. The moment that I turned the ignition switch, the built in fuel pump kicked in (although for only 10 seconds at a time). I also learned that the rear "Relay O" controls the fuel pump.

I've been able to get nearly 10 gallons out until I'm sucking air. The fuel line is blowing bubbles, and I can hear the motor from the fuel fill tube. I can't siphon anything from the fuel fill tube.

I should still have a half tank to go! The fuel guage shows 1/2 tank as well. I'm really confused. How can a be sucking air with at least 5-10 gallons still in the tank?

Is there a second motor? Is there a second relay or fuse that I'm missing?
 
#2 · (Edited)
The tank is a saddle type, the car is rear wheel drive and it straddles the prop shaft.

So the "other" side will dribble slowly through via the small "balance" hose that connects the two sides of the tank.

If you can find and disconnect that balance hose you should be able to suck out most of the remaining fuel through it.

Some rear-wheel drive cars have two fuel pumps, one in each side of the tank.

The W164 holds 95 litres (25 US gallons, 21 UK gallons).

Diesel is a light oil and lubricated the engine. Gasoline does not lubricate the engine and will cause damage if the mistake is not realised in time, as the cylinders run dry.

You can also fill the tank with diesel and suck it out again then refill with diesel a second time. That's going to cost you a wasted tank of fuel, unless you have a diesel tractor or truck to use it in, but that's nowhere near as much as a mechie would charge.

A small amount of gasoline, a couple of gallons at the very most, won't hurt the engine as long as you fill the tank full with diesel before starting the car.

Some old diesel fogies deliberately put a couple of gallons of gasoline in diesel cars once a year to clean the top end of the engine, valves and injectors.

The other way, diesel in gasoline cars, fouls up spark plugs and valves and injectors, causing lumpy running, and misfires, (and can cause catalyst damage), but that usually clears after a couple of tankfuls of gasoline if it's realised and caught in time.

Don't forget to change your fuel filter too.



So you should be OK. Let us know how you get on.