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  #1  
Old 04-26-2016, 01:19 PM
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fuel caps rusting out

The metal part on the inside of my original fuel cap for my 99 E300TD was pretty rusty so I replaced it about a year ago. The new one is already rusting pretty bad. When I remove it often times I can see water/condensation on the metal part. Is this a common? Any ideas what could be causing this, and what I could do to prevent it?

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Old 04-26-2016, 02:19 PM
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I see this too in my 1984 & 85 300D's, and it is much drier here. Might just be in the winter that I see clinging drops. Water in the fuel isn't good since biological creatures find that appealing, but I haven't found any black slime yet. I do have some treatment from a truck stop that claims to both kill it and disintegrate so it doesn't clog the tank filter. Rusting the tank is another issue, though haven't read of that being a problem on these cars.
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Old 04-26-2016, 05:46 PM
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Same thing on my 98 E300 as well. My 87 300TD cap is rust free. Only difference is the wagon sleeps in the garage and the E300 sleeps in the driveway (or the airport). Both get fueled at the same station by my house.

I wonder if they changed up the tank venting between the 210 and the 124.
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Old 04-26-2016, 10:16 PM
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If moisture is collecting on the caps, check your tank vent and tubing... You may have lost it... Don't park with the tank low....
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Old 04-26-2016, 11:27 PM
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I have the same problem with my '98 e300td. My last cap lasted about 10 years. In February, I couldn't get the cap off due to rust when I stopped to fill the tank. I hadn't removed the cap in about two months. I could turn the cap with ordinary pliers but could not remove it with my hands. I used a pair of plumber's pliers that has a wide mouth. I pliers at 12 o'clock and 6 o'clock. I learned the hard way that the dealer charges $48 for a cap. PP sells a Bosch cap for about $12. (I live in northern Virginia, just outside the District of Columbia.)
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Old 04-26-2016, 11:58 PM
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Quote:
Originally Posted by vstech View Post
If moisture is collecting on the caps, check your tank vent and tubing... You may have lost it... Don't park with the tank low....
Wouldn't happen to know of a place to start looking for a diagram or tutorial on this for the '99 E300TD, would you? Mine started rusting badly at about 9 years of age timeframe.

Last edited by Skid Row Joe; 04-27-2016 at 11:26 AM.
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Old 04-27-2016, 09:09 AM
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My '87 sits all winter in the garage, changing temps, tank between 1/2 and full depending on whether the salt and snow surprises me, ... cap looks clean and silver inside and I've never replaced it. It does always sleep with RedLine in the fuel FWIW. My '93 300SD has an all-plastic aftermarket cap that might be a good solution for the 210 guys, but I'd still worry about the tank and filler tube getting moisture.
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Old 04-27-2016, 11:03 AM
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I had this problem on my W124 which then didnt re appear after I once removed the tank to clean it like a madman (strainer cleanup job gone wild)
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Old 04-27-2016, 11:37 AM
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There will always be moisture condensing on the fuel cap due to temperature swings from day to night. You can lessen the amount by keeping the tank full. The issue is with the lousy plating on the cap, which has worn off. You can stop it from further rusting by smearing a light film of wheel bearing grease on it every so often.

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