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W-1-2-3 Go!
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Discussion Starter #1
The R light turns on around 200 miles, give or take a few more. But, the fuel gauge reads 1/2 tank when the R light turns on around the 200 mile mark. I think the last fill up was 15 gal. So that may point out that I am in need of a tune up since I get 16MPG. Is this MPG really bad? Is it also a faulty fuel gauge, sender, or something else? (not familiar obviously with 124 electricals)

Temp gauge also shows it runs cold, and fluctuates from 80 to 60 and back. Radiator is new, coolant is a bit low but should not affect cooling right? Thermostat, no idea. Haven't replaced anything yet really since we got it Jan 2007.

Should I look for an electrical problem first? If so, how? If not, what to do?

'90 300TE :thumbsup:
 

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About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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5,501 Posts
Replace the thermostat. The only time the gauge should read 60 is when the needle is on the way up during warmup.

16 mpg isn't great but a lot depends on the type of driving you do and your driving style.

Regarding the fuel gauge problem, the combination of 1/2 tank readings with reserve light on is weird. The sender is just a float that rides on a spiral-wound strip housed inside a tube. The strip rotates, operating a potentiometer which provides a signal to the gauge unit. I think the gauge itself contains the reserve light circuitry and when the sender signal drops too low for a specified period of time the circuit "latches" and turns on the light. I hate to say it but the problem sounds gauge related to me.

Swapping in a new sender on a sedan is very easy. It's done from inside the trunk and you can do it with a full tank of fuel. On a wagon, however, I don't know. I bet it's harder than on a sedan though!
 

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'84 300D/ dakota benz trk. Sold... miss it. "88 260E '91 190E 2.6 '89 Volvo 240DL "85 300D
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1,252 Posts
negative, the part of the system that tells reserve light to come on is in the sender itself. replace or repair. i would replace.
 

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Premium Member
W-1-2-3 Go!
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16,161 Posts
Discussion Starter #4
Is this the same as in the 123, where the fuel tank is below the cargo bay (and provides easy access with the 3rd row seat out)?
 

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'94 E280 T
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587 Posts
Karugs,

The sender is below the backrest of the 3rd row seat.

Remove the carpet (a few plastic clips on the inside) and you'll see it. Thing is, you'll neet a huge socket to remove it (bigger than a 30mm socket IIRC).
 

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1987 E300 W124
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85 Posts
i have the same problem i was told that where it reads the fuel level the senser if you will is cloged up or dirty thats what i was told about my fuel gauge it does the same thing but it bounces too
 
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