Wow sorry to hear this. Potassium hydroxide is a caustic and an excellent degreaser. It comes in crystal flakes in it's dry state and is mixed with water. It will etch aluminum if left in contact and slowly dissolve it. Drain and flush it out ASAP. Not sure what it will do to the tank since it's terne coated (lead and tin) but the fuel gauge sender tube is aluminum and the fuel strainer is aluminum, so is the IP case and fuel filter head. Water is heavier than diesel so the potasium hydroxide water solution will sink to the bottom and do it's job there. You may find the bottom of the fuel sender and fuel strainer black from being etched by the caustic, probably won't harm it's operation. Is your neighbor gonna buy you a new tank and IP for your Bday present?

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

starts with sh & ends with t & you find it in the bottom of a birds cage & its not shell-grit ~ too many letters

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Wow, what a truly disheartening story. So much for accepting gifts from your neighbors . . . . eh?

__________________
" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles

Happy friggin' birthday!

__________________
" We have nothing to fear but the main stream media itself . . . ."- Adapted from Franklin D Roosevelt for the 21st century

OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles

Ok. When I got home last night I saw the containers of diesel and **** that my neighbor had pumped out. This morning I clamped off the lines going to the expansion tank and the return line. Pressuized the tank with a shop vac and white foamy **** started coming out of the fuel line. I pushed that out until I was getting air and then added a few cups of diesel. It apparently turned into the white foamy **** and it came out the fuel line. Did the same thing again with a drill pump attached to the fuel line and got the same white foamy ****. Any suggestions how to flush the tank? Another liquid instead of diesel? If so, what?

__________________
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

Maybe it's just D2 foaming under pressure. Does it foam if you reduce tank pressure?

Sixto
87 300D

It seemed to be foaming as much with the drill pump as when I pressurized the tank.

__________________
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

I would try flushing with plain water first, maybe a couple tank fulls.
Fill the tank, let it sit for 30 minutes or so then drain well, then repeat.
Then use a couple gallons of methanol to absorb any water left in the tank.
If you can, slosh it around by rocking the car.
Drain and blow that out well and let the tank sit open for a day or two.
The water should clean out any residual lye and the methanol any residual water. By chance if there is any residual lye it will dissolve in the methanol as well.
Once it is thoroughly dry fill it with diesel.

__________________
Darrell

1984 300SD "Ole Girl"
207K

More info. I removed the tank strainer. The problem is complicated by the fact that this is a TD and not a sedan. The TD fuel tank has two chambers, the main chamber and a lower second thin chamber maybe 1/2" deep. The outlet draws from the lower chamber and fuel moves from the main chamber into the lower chamber via the tank strainer. Of course, the nasty ****, having a specific gravity greater than diesel moved into the lower tank and mixing fresh diesel or water or whatever with the fluid in this lower second chamber is not as straightforward as it would be in a single chamber tank. I assume the tank is designed this way because it is mounted flat and this two chamber system retains fluid in the outlet portion of the tank when the tank is low and you go around a corner.
Thanks to Chad300tdt who has a little diagram on the forum explaining this oddity in the TD tank.
300TD tank strainer

__________________
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

I would try adding a little white vinegar to the water. You put a strong base in there so you should be able to neutralize what is left with an acid. I'm not sure what the chemical reaction between the two would be though. YRMV

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

I had about a cup of stuff I pumped out in a bottle. It was white/grey foamy **** with about 1/4" of diesel on top of it. I poured about a quarter cup of white vinegar into the bottle and shook it up. Didn't seem to make any difference at all. I'll monitor that bottle to see if time changes things.

__________________
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

order listed above

Man, I would be looking at the u-pull it for at least a new tank, I think. What a PITA!

__________________
1976 Mercedes 240D, unknown mileage
1992 Dodge/Cummins 4WD, 284k

Kerry,
The tank needs to come out.

I guess its unlikely that you could get another tank being a TD.

With the sample you have, experiment to make sure its soluble in water & if it is soluble, water will do the trick. By experimentation on your sample of the s##t, you can see what will happen if a substance is used. unleaded gas is worth a try on the sample first.
If water mixes with the s##T, try inverting the tank & filling with water through the filler, you may be able to get all the s##t to come out the fuel line.
Air pressure does not appear to be your friend, water pressure may work better.
If you know any one with a boiler in a factory, you could steam the tank for a day. We do that on tanks to remove fuel before welding. It has the extra positive of heating the tank so if drained, it dries right out. If not, very hot water may be a substitute.

The tank will eventually be good, the IP is more of a worry. Best drain & flush a few times, not with water. The hard lines & injectors should ideally be removed & cleaned. Did the diesel purge mix with the s##t?
Does your neighbor know what the s##t is?
I guess at the moment you are between a rock & a hard place!!
Be very methodical in what you do, no knee jerk stuff, logical planned steps will get you on top of the problem.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

X2. This makes sense, at least for the tank & lines. The sequence is important in order to first remove the KOH, then the water. Stuart's a chemist... he knows what he's talking about.

__________________
-1985 300TD - 324k mi on chassis. MB "Tauschaggregat" 617 motor + 4-speed conversion
Alaska Roadtrip 2009
-2002 E320 Wagon - 197k mi
-1998 E320 Wagon - 310k mi - retired