I have an 82 300TD, and I was looking through my owner's manual trying to find out at how many gallons the fuel light was supposed to come on. In the process I discovered that the manual says there is a reserve fuel tank. Is this standard equipment on all these cars? If so where is the reserve tank in my wagon. I read a few posts on this forum saying it was behind the spare tire, so I looked, and there is some kind of tank there but it seems like a strange place for a reserve tank. These cars just keep surpising me. Also when will my fuel warning light turn on?

Thanks for all your wisdom
Andrew

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When the manual calls out the "reserve fuel tank", could this be simply the "fuel reserve". The reserve is the fuel available in the main tank when the light comes on. It's typically 2.5 gallons or so.

Or, is this a completely separate tank??

wagons did have an optional fuel tank which is found on ebay once in a great while (and was fitted in place of the spare), but all w123 ( I believe) wagons will have a fuel overflow tank behind the spare- looks like it could carry a gallon and a half.

So the W123 sedans dont actually have a separate reserve tank then?

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1985 CA 300D Turbo , 213K mi

i dont think any of them have an actual reserve tank, in the wagons and in sedans there is a vacuum reserve tank which is black plastic. and in the wagons there is a windshield washer tank which is white plastic. i have never seen a reference to a reserve fuel tank or an overflow tank.

brian is correct in saying it is only in the main tank. the warning light is to tell you you are near the end.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I don't think it ever says fuel reserve "tank", I think it is just fuel reserve. Either way, it is just a reference to some fuel still available after the light comes on. The wagons do have an expansion tank in front of the spare. I'm guessing the wagons have one and the sedans don't do in some reason to the wagon tank being more flat, and the sedan tank being more upright. (maybe?)
Heck, what do I know.......

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

i never saw one. but if there is it is because of as you note the tank is flat and the filler is lower so it is more prone to overflowing.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The fuel tank for a 300D Turbo is listed as having a capacity of 21.1 gal with a 2.8 gal reserve, is the reserve included in the 21.1 gal figure, or is the true capacity 21.1 + 2.8 = 23.9 gal?
-Joe

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

That is your total capacity. The reserve is actually a portion of your tank. You can't really see it but there are raised walls in the tank I believe so that when fuel is low, it still stays by the fuel lines. I'm pretty sure that's how it works or it least how I understood it. So the tank is just one tank with a portion in it being capable to handle 3 gallons or so.

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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Speaking of fuel:

The SDL took just under 20 gallons today. However, on the highway, just prior to fuel, it had no power. Didn't miss or slow down, but would not hold an upgrade at 65 mph without a downshift. Acted like it had insufficient fuel.
It would rev to 4K on the downshift without a problem.

In theory, it had another two or three gallons in there. The reserve light was not on yet.

Who knows, maybe it was the placebo effect.

My '80 is like that. It will cough and sputter with no power before the light comes on. I know the light works cause I drained the tank and it would come on. Then added a couple of gallons + before it went out. But it won't run down that low and run properly. Of course, running properly is something this car hasn't seen in awhile unfortunately....

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

I think I heard someone mention something similar when the fuel screen is getting clogged or another fuel filter. I assum you checked the clear filter?

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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I haven't looked at anything yet. Just reporting events.

could be something in the tank floating and got on the sock when the tank is low.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Well, I took it half way home (about 100 miles) and the "problem" remains. However, it's even more interesting:

When stuck in bumper to bumper traffic, apparently the system develops normal fuel pressure and you have the boost when you finally exit the bumper to bumper traffic. Then, after a short distance of 2700 rpm running, the fuel pressure drops and you've essentially got a n/a 240D underfoot.

It won't hold 65 mph on any half way decent grade.

Hope the fuel filters cure it. I can't get the tank screen out without the proper 46 mm. socket. BTDT.