I installed the repaired dented tank and rebuilt squashed sender this past weekend in the 300TD and thought I was done. The ride into work yesterday was fine but when I went out at noon the motor would not start. I gave the primer about 20 pumps and nothing was flowing. I removed the filler cap and swoosh!! air rushed in and I heard a bonk from the tank.

@##@%*^% I can't believe it!! One of the disadvantages of filling up in NJ is that there are no self-serve pumps, so I never get the opportunity to open the filler myself. Fortunately the tank seemed to pop back into shape. Unfortunately I could see a slight impression of the sender on the tank bottom. Sure enough when I got the engine fired and drove the fuel gauge was going nuts with the needle cycling between full and empty.

Last night I pulled the sender and found the bottom of it was squashed again but not as severely as the first time. At least the center rod was not broken as before. However the rod must have been pressed further into the cap as the sender wires were all floppy. They must have been shorting on the can making the needle swing. I left a little tail of wire at each solder joint from my previous repair so I was able to heat and retension the wires. I had to hammer the can back into shape and remove about an 1/8' from the length to match the shortened rod. The sender now looks really ugly but it works ok. Fortunately the loss in length was not enough to throw off the readings.

I checked the 2 small vent lines from the tank and one of them had some fuel inside but all the lines seemed clear both to the tank and canister. I filled the tank Sunday night so maybe this problem occurs only with a completely full tank.

Anyway rather than trying to sort out the venting system I popped the black cover off the fuel filler cap. I drilled 2 .050" diameter holes that fell inside the center boss through both the steel cap and spring washer. This puts the holes in direct communication with the filler tube but hides them from splash under the center boss. I also drilled the same size holes in the plastic cap and oriented them 90 degrees from the holes in the metal cap.

This morning I checked the cap a couple of times coming to work and there was no vacuum at all so hopefully I have it knocked this time. I guess the next full tank will tell the tale...

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Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)