1980 Sl ran great until it ran out of gas

[Phil V]

A buddy of mine recently bought a 1980 SL 450 for his wife that is a very nice low mileage one owner car. It ran great until she ran the car out of gas. A gallon of clean gas was poured in the tank to get it to a gas station where another 8 gallons were put in the gas tank. Now it runs good for a couple blocks then runs really bad. the fuel pump is making a high pitched sound like its starving for fuel. The logical problem from my perspective is the fuel filter is plugged up. After the car sits for a while it will start and run smooth again for a couple blocks then runs bad agian. Any help will greately be appreciated. I own and operate an autobody/paint shop so I have all the tools (no special mercedes tools) and the place to work in the car. Thanks, Phil

[280sleuro]

I had the same problem with my 280SL. It turned out to be a dirty gas tank. There is a very fine mesh screen filter inside the tank where the main fuel line is. I had to remove the tank and flush it out and clean the screen filter. Ran great for about 100 miles, then happened again (noisey pump). This time I took the tank to a radiator shop that acid cleaned it. It's been running great ever since.

[rocky raccoon]

Probably sucked up a lot of sediment from the bottom of that 28 year old fuel tank. Change the filter. Easy and inexpensive to do. No special tools required. If that doesn't fix it then you can sweat the expensive stuff.

[ctaylor738]

The trouble with your theory is that the flow is from the tank to the pump to the filter, so the starvation is caused by crud in the in-tank mesh filter. You need to drain the tank and remove and clean the filter. You need to remove the tank outlet hose with a 19mm crowfoot, then the filter comes out with a humongous special socket (46mm?). If you are lucky, the larger fitting may come out with the outlet hose. In any case, be sure to have a new o-ring for the tank fitting on hand.

It would be smart to replace the tank hose while the fitting is out.

There are a couple of very good posts on this miserable job that will come up if you do a search.

After this, I would suggest adding gas and joining the feed and return lines at the engine. Then jumper the fuel pump relay, let the pump run for a couple of hours and then install a new filter and reconnect the lines. If you allow any finely ground crud to get into the fuel distributor, you are in for some serious dollars.

[rocky raccoon]

For CTaylor:
Chuck. Although they have been doing it for many years, runniing unfiltered fuel through the pumps seems to be asking for eventual trouble. Would it be worthwhile to install an in-line filter between the tank and pumps? I know this is tangential to the primary issue on this post but what do you think?

[Strife]

This style of fuel pump actually uses fuel for cooling, and i suspect that it is VERY BAD to run out. I lost TWO fuel pumps on a GM car this way, at $300 each time (in tank).

I NEVER let myself go below 1/8 tank.

[ctaylor738]

I tried this on a 280SE with rust problems, and it worked OK until I had the tank boiled after which I removed it.

But I don't think it's a good long-term solution. My theory is that the pumps push a lot better than they pull, and any restriction on the inlet side would cause problems. I think that's why they have that giant hose and no filter, to make the feed to the pump unrestricted.

[Roncallo]

Originally Posted by Strife

This style of fuel pump actually uses fuel for cooling, and i suspect that it is VERY BAD to run out. I lost TWO fuel pumps on a GM car this way, at $300 each time (in tank).

I NEVER let myself go below 1/8 tank.

I remember going to a Bosch seminar back in 1980. The concept of the fuel pump armature being submerged in gas kind of struck everyone odd. The conversation went something like this.

Cant that blow up
No its submerged in fuel so there is no air available for ignition
What about when you run out of gas.
It's never happened.