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Old 08-25-1999, 03:59 PM
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Join Date: Jul 1999
Posts: 239

The low fuel warning does not light up during glowplug warmup on the 81 300SD...Which means not likely when fuel is running low either.
Would I be able to investigate under the first aid kit or is something faulty in the tank ?

Old 08-25-1999, 10:14 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
If it is not lighting up when the key is on and the engine is not running, the bulb is most likely faulty. This usually will have nothing to do with the sending unit!


Old 08-25-1999, 11:09 PM
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Join Date: Jul 1999
Posts: 239
Thanks, Benzmac.
Just got my two volumes of body chassis manuals...will try to get to the bulb and check it.
Old 08-26-1999, 02:42 AM
Posts: n/a
My low fuel light doesn't come on when I turn the key but it DOES come on when I have low fuel. I don't think it's supposed to turn on during the glow plug phase, maybe mine is an anomaly. Try running your fuel close to down (but don't run in down!!) before you start playing with the dash. Good luck.
Old 08-26-1999, 03:36 AM
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W140 Maniac
Join Date: May 1999
Location: Burnaby, BC, Canada
Posts: 960
To Lube,

Which model do you own??? I have '92 400SE(W140), and the fuel light DOES come on when ignition is on without engine running. Just to let you know....

Andy Kuo
'92 400SE
70,840 KM
Old 08-26-1999, 09:36 AM
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Join Date: Jul 1999
Posts: 239
The low fuel light should come on initially, along with most of the other warning lights, at the last click of the ignition key before cranking the engine.
I am not about to find out if the light comes on by risking running the tank near empty and ending up sucking up all the bottom junk on the diesel tank and end up with more problems.
My guess is if it does not come on during preignition, not likely to come on when fuel is low ?
Sure hope it's just a bulb in the instrument (as Benzmac suggested) because I have to remove to cluster anyway to investigate the trip meter that's not working.
(Benzmac already offered his tip for that problem on another post, by the way.)
Old 08-26-1999, 11:53 AM
Posts: n/a

mine is a 81 300SD. Perhaps mine has a gremlin in it. The light turns on only when the meter reaches the second to last marker. It never comes on during pre-ignition. Sorry for the confusion, sounds like mine may be buggered. Thanks.
Old 08-26-1999, 12:37 PM
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One advantage of running your fuel tank low is that if you are so inclined, you can replace the fuel tank screen and the associated hose that screws into it. An opportunity to get rid of any crud in there. I have seen a diesel tank screen come out of a diesel with about 223,000 mi. on it with no debris build-up at all: my '83 300CD-T. I was disappointed after running the tank low and buying a new screen, however, who would've thought?

Also, if you are going to pull your instrument cluster: If your car has the rheostat that dims the cluster's lights, check to see if it is working ok before pulling the cluster. If it isn't, you might consider replacing it while you have the cluster out. Lastly, be very careful while the cluster is out, some have screws and the like that protrude from the back and if you are not extremely careful, you can inadvertently allow those protrusions to dent your dashboard.

Good luck-

Old 08-26-1999, 12:51 PM
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Join Date: Jul 1999
Posts: 239
Hi, Terry -

Thanks for the warning tips on the instrument cluster. Certainly don't want to ruin the dash top which is still as new. Rheostat is fine.
Going to rig up an "L" shaped tool to unclip the cluster and will be very very careul.

As for the tank, it was recently replaced (at the dealer) - the debris I'm concerned about is actually algae sludge buildup I've seen mentioned at various postings, although RedLine is supposed to help. Maybe this algae problem is prevalent only in certain parts of the country ?

81 300SD 193,000 miles.
Old 08-26-1999, 01:16 PM
Posts: n/a

Sounds like you're in good shape with the rheostat and the fuel tank screen.

On pulling the instrument cluster:
I have a picture on my other computer of a tool that someone made for this purpose. It sounds as though you already know what you're doing, however, if you like, I can e-mail it to you within a day or so (post your e-mail address if you'd like). Also, you might be interested to know that for my M-B (300CD), I have been able to remove the cluster without using the the hook tool. Essentially what I did was to remove the panel above the driver's feet and just use my fingers to gently push the cluster out. For all I know, the hook tools make the job easier but for what it's worth, I did it another way.

Good luck-

Old 08-26-1999, 01:21 PM
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Posts: 239
Thanks, Terry !
Old 08-26-1999, 01:27 PM
Posts: n/a
On algae in a diesel's tank, I'm not an expert on this subject, however, over the years I have read of several causes:
1. The same fuel sitting in the tank for a long time (months).
2. Humid environments seem to encourage it.
3. Facilities that sell diesel that may not turn much of it over and/or have algae in their tanks.

The only remedy I've ever used is Biobor's product for eliminating algae.

Anyway, just what I've read on the subject-
Old 08-26-1999, 01:50 PM
Posts: n/a
There was a recent thread about algae on the newsgroup. Check it through if you like.

Couple of things that came up: if you want to clean it be prepared to spend a lot of effort doing it. One of the options was removing the tank and boiling it... Another problem is that using an algae fighting product will produce a lot of dead algae, which may do more harm than good by clogging lines and filters.

On my car I'll peer in the tank from the access thing at the top when I clean the sensor and unless I find creatures lurking in there I'll leave it alone.

Old 08-26-1999, 02:46 PM
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Join Date: Jul 1999
Posts: 239
Yup, that's where I saw the discussion on algae, including boiling the darned tank, before I fled to this site.

Now I'm losing track of what started this discussion....Oh, yeah, the low fuel warning light. Anyway, as soon as the weather cools down (= no mosquitos) I will venture into instrument cluster removal.

Thanks for the input.
Old 08-26-1999, 08:52 PM
Posts: n/a
According to the 123 CDROM, vehicles

prior to September 1982 only show the

low fuel light when the fuel level

reaches the prescribed level. Vehicles

built after September 1982 display the

low fuel light when the key is first

turned on. After the engine starts, the

low fuel light returns to normal function.

Algae in your diesel fuel tank grows

along the line between the fuel and the

water in your tank, getting oxygen from

the water, and nourishment from the fuel.

If you add biobor to your tank to kill

the algae, you will change your fuel

filters many times before you rid your tank

of all the dead algae. If you have a lot

of algae, you would be better off removing

the tank, losing the water, and flushing

it out to eliminate the source of your

problem. Those of us in the fuel injection

business would lose half of our work if

it wasn't for dirt and water in fuel. Sad

but true.

Bosch certified DFI Tech
20 years experience
MBCA Member, Southern Stars
1984 300D
1985 300CD
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