Obtained a 90 liter tank for my 87 300d from a local pick n pull.
Salvage yard punctured the tank with 3ea 1/2" holes to drain tank.
Looking for 3ea 3/4" steel discs to Tig weld over holes.
Not too thick, not galvanized.
Any ideas?

Go to a shop that works with sheet metal and ask for a handful of scrap discs from their punching operations.

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Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

WARNING: this post may contain dangerous free thinking.

I'd just cut something out of sheet metal with tin snips.

Electrical wall switch / outlet boxes have knockouts but are a bit thick / lightly zinc coated.

Disconnect switch or breaker boxes have thinner material that is generally painted.

Best to solder them on. The excessive heat of welding will melt the protective sacrificial type metal coating that is applied to both sides of that type of steel. As a rust preventative. In the general area of the weld. Also you probably do not get a really good weld when it is contaminate by that coating . The fumes would not be good remember if you do weld either.


I forget the trade name of the type of steel used to fabricate gas tanks. Maybe tern steel named after the factory that originally produced it? It is special though and has an applied coating on both sides by the steel manufacturer in production as protection from the steel rusting. They just put on less and less or changed the metal consistency of this coating over time.


So gas tank failure became a real big issue and we have plastic tanks to replace them now in general. I have dealt with gas tanks from the 1930s and 40s that were still like new because that coating was so thick on the steel. I suspect when they thinned it down so much as it was sacrificial metal. Time breeched it by electrolysis perhaps.


Properly soldered patches are more than adequate. Plus more likely not to seep. Or rust externally with time. Easier to do a good job on as well in my mind.


There are two gas tank related problems posted right now. I will go give my opinion for what little it is worth on the other post now. Both are just opinions based on some experience. Nothing is written in stone.

Galvaneal ( SP ? ) is one type of coated steel. This is where a thin coating of zinc is added rather than hot dip like a garbage can.

Galvaneal is very weldable as is not like hot dip galvanize.

Galvanization is easy to buzz off too, couple passes with a flap disk and mostly gone. Base metal will be somewhat contaminated, but it'll be fine. I believe there is "cold galvanization" in a spray can available now as well, if you feel like recoating afterwards.

I'd lean towards one of the common fuel tank repair epoxies, first.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

Problem solved. Ended up getting a piece of 16ga steel from Home depot and cutting my own discs with a hole saw on a drill press. Pilot bit removed.
Had them Tig welded by a friend today. Weld looks well done, professional looking.
I'll paint over the affected area and that's as good as it gets. Can't imagine having any rust issues. Tank was in excellent condition to begin with.
Should increase the cars range to 650-700 highway depending on load.

Assuming ~30mpg and you use every drop of fuel in the tank, sure you can get 700. Let's be realistic, you're gonna be refilling ~20 gallons, not the full 23 gallons that the tank holds. Realistically more like 560-600 miles highway doing 28-30mpg and 100% highway.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

With the 90L tank I've done over 900 miles on a fill up. The low fuel warning comes on at 2.5 gallons and that gives me another 100 miles on the highway. In my 87 300D/5spd/90L LA to SF to LA at 75mph is easy. Also from my experience the real usable capacity of the tank is closer to 95L.

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I was wondering how the low fuel light would work with this tank. Looks like the same sending unit is used in both tanks. Car gets 31mpg with no load @ 75mph. 28 with moderate load, 26 when sagging in the rear (4 persons with luggage) 95L would be sweet! I assumed the tank volume was exactly as listed.

The 90L diesel tank is internally identical to the 90L tank fitted to the 500E. Since the fuel consumption on the 500E is much higher they fitted a shorter fuel sender so the low fuel warning would turn on earlier. I fitted my 70L sender in the 90L tank because it was in better condition but it is indeed identical.

Diesel tends to foam a lot while filling so when the pump clicks off, wait 10 sec and restart the pump. You'll get another gallon in at least. Also the tank is designed with about 20% air space at the top for gasoline fumes which diesel fuel doesn't have. The interior volume is closer to 110L with about 95L usable.
70L to 90L W124 fuel tank swap pics

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Would you mind sharing how you're doing 40mpg at 75mph in an '87 300D? I'm sure a lot of us would be genuinely interested in knowing.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

5 speed manual transmission with 0.8 overdrive 5th gear, lowered front suspension, full underbody aero cover, increased injection timing, no viscous clutch fan, electronic boost controller, electric fuel pump, modified ALDA, EGR delete, monark nozzles, R230 alternator with OAP.
5spd (Mercedes-Benz 300D) | Fuelly

And minor correction, it's closer to 38mpg @75mph, 42mpg @60mph

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Did you change the rear end ratio? A/C? Tire pressure? I do 29-30mpg highway in the SDL, I don't think there's any real room for improvement in that barge, but the 124 has potential.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Rear end ratio is still the same 2.64 but with 5th gear the engine is turning 20% slower in paper. In reality it's closer to 25% slower since the stock 722.3 lacks a locking torque converter.
I use AC in SoCal almost all the time.
The 300D weighs about 500lbs less than the SDL and has a better drag coefficient so I don't think the 126 body could match these numbers but a manual swap should offer a similar % fuel economy gain.

Before 5spd swap.

After 5spd swap.

Revs @ 70mph

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