The manual says the fuel tank holds 18.5 US gallons. Today I ran out of fuel, and when I filled the tank, it only took 14.8 gallons, which leaves me with 3.7 gallons that were apparently unusable. Could I have the suction and return lines swapped? Under the hood the return is on the upper line and the suction is on the lower...

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

I think the upper is the supply, and the lower is the return on my 123's...
the wagon tank is on the bottom of the car, you could have hit a rock or somehting and reduced it's capacity.
I've always assumed 16 gallons in my wagons. it's REALLY hard to top them off though. that air bubble sure does take it's sweet time burping!

nope. you have it right.
upper is return, and lower is supply! (makes sense, as the return comes off the fuel filter, and the supply goes to the primer pump down low... if they were swapped, they would have to criss cross themselves.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Did the gauge read "empty"? You may have a clogged strainer. I thought it was 16, with a two gallon reserve. I always used to shoot for 120 miles per 1/4 tank. That usually came out to about 30 mpg.

Jay.

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On the road, currently:
'83 300D (German spec.) 168k mi. - - Wolfgang (tucked snugly away for the winter!)
'87 300D 375k mi. - finally went over to "The Dark Side"
'87 300TD 225k mi.
Cannondale 66cm CAAD5 w/Campy/Jamis Aurora
Hujsak Custom Fixie/Landshark Track Shark Custom/Ahearne Custom 29'er

The gauge read about 1/8 tank, but it's a little erratic. I don't think it's the strainer, unless putting fuel in the tank unclogged it. The fuel filter was empty when it ran out.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

It is possible - trust me - for only the lower part of the strainer to be clogged.

Jay.

__________________
On the road, currently:
'83 300D (German spec.) 168k mi. - - Wolfgang (tucked snugly away for the winter!)
'87 300D 375k mi. - finally went over to "The Dark Side"
'87 300TD 225k mi.
Cannondale 66cm CAAD5 w/Campy/Jamis Aurora
Hujsak Custom Fixie/Landshark Track Shark Custom/Ahearne Custom 29'er

I've never got 18 gallons in my wagon. I'd be really surprised if it holds that much. I've run it down so low that the engine cuts out around corners.

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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

yeah, if the lower part of the strainer is clogged, when fuel gets below the clear part, it's going to suck air and act like an empty tank.
when you get the tank full, try reversing the lines for 1/2 a tank... and put a serving of startron in there...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thanks, guys. I've been thinking maybe I should pull the strainer anyway, so I may give that a shot next time the tank is low. God only knows what's in there.

__________________
1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png