Yup. After 2.5 years of driving this car, that's the only thing I can pin it down to. It'll start up perfectly every time I need it to, but when I fill it all the way up at a station all I hear when I turn the key is a click. It starts just fine if I don't fill it all the way up.

Someone showed me a trick to get around this, though I don't know what the problem is. I take a wrench or something metal and connect the two wired-bolts on the starter solenoid. This causes the solenoid to pump. Then I go back into the car and it starts.

Something to possibly note is that my fuel gauge is shifted to the left a little bit - so when it's all the way full the needle is only a little over the 3/4 full mark. And on empty it goes past the empty line. Any chance this is related?

I've asked around about this problem, but haven't gotten much but blank stares. It seems unlikely that it's a starter problem since I have absolutely no other problems starting, ever, and this only happens when the tank is completely full. Seems like some sort of electrical or vacuum issue related to a full fuel tank. One person mentioned some cars have a vacuum related system for marking when a fuel tank is too full or something like that.

I'm about to go on another road trip, so it'd be great to be able to fill my tank up all the way without getting dirty. I can't imagine my work around is any good for my solenoid either.

perhaps the Engine ground is positioned such that it moves slightly when the weight of the "full tank" loads up the rear of the car.......

...try using your jumper cables and connecting the negative terminal directly to the block.....then try with the key......

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG

I can give this a shot - then I should also be able to reproduce this by loading up the trunk with lots of weight.

I should really check out all the electrical connections in there too. Would I do this by tracing everything from the battery and disconnecting/reconnecting and cleaning every end? Just afraid my workaround may have warped the threads on the solenoid...

After it fails to start to see if it is a ground problem why not try hooking a Jumper Cable from the (-) terminal to the engine block and see if it works.

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84 300D, 82 Volvo 244Gl Diesel

jumping terminals one and three in the junction box on top of the fender in front of the battery will do the same thing without screwing up your threads.
This symptom is pretty common on 123's but no one has correlated it to a full tank of fuel before to my knowledge. Cause could be a bad ground but it has typically been attributed to dirty contacts in the ignition switch. There's a thread here somewhere describing how to clean it.
My TD does it periodically. I carry a small piece of wire to jump the terminals. Then it will be fine for a few months.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

After I left work I was provided with a great opportunity to test this! So I guess it does happen outside of fill-ups.

First I tried kerry's suggestion of connecting terminals 1 and 3... nothing. Then I tried the jumper cable grounding from the battery to the engine block, and... success! It started up. Guess I've got a bad ground, and sure enough, I did put more fuel in this morning than it's had in a while, and there is more weight in the trunk. Odd that weight would set it off, but I suppose this should be an easy fix? Just clean the ground wire ends and check for corrosion?

By the way, thanks for everyone's prompt responses. What a helpful forum!

Check especially the engine-chassis ground located near the starter.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Not that it's particularly related to the problem... but at least as a temporary work-around to the problem if it bothers you, I always leave mine idling while refueling.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Just cleaned up the battery terminals really well. The battery ground looks good.

SD Blue, I couldn't find the engine-chassis ground, though I looked all around the starter.

I did check out the connections to the solenoid, and they looked good. But as far as I could see (which wasn't much), the thick cable that goes from the solenoid to the starter might be my problem. I couldn't see the cable or the starter bolt at all, but the bolt on the solenoid did seem a little white around the edges, so it's possibly corroded?

Is there a good place to clamp the jump start cable onto the engine? I couldn't find one. Or is any solid and connected spot on the chassis fine too?

Sorry 'bout all the questions, and thanks for all the help so far! (today I replaced my fuel/air/oil filters, changed my oil and did a diesel purge, things are running quite fine! next is a badly needed valve adjustment, if I can find some wrenches...)

The W123 chassis is a little different but from my understanding the ground strap is located in the same general area. Try looking a little forward of the starter as mine was going from the chassis to the exhaust clamp originally.(In fact, the exhaust clamp had loosened and was causing my intermittent starting problems.) BTW, the manifold is generally a good ground connection.

For the valve adjustment, I've always used ordinary 14mm open-end wrenches. One needs to be a little thinner in order to loosen the locking nut and it may be a little more difficult but still doable.

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Sam

84 300SD 350K+ miles ( Blue Belle )