I pulled into work yesterday and noticed a serious leak along with a trail of fuel on the parking lot. After tightening both fuel filters and inspecting the new fuel thermostat there was no change. The fuel looks like it's falling off of the bottom of spin on fuel filter at the front, but I pulled it off and determined there was no hole in the filter and the rubber gasket at the top was not leaking. Everything's soaked with fuel under the hood because of the belt flinging the stuff around so it's very hard to determine visually what's causing it. The leak only happens when the engine is on and is between the injection pump and spin on fuel filter. What is most likely the problem? I'm hoping that the injection pump is fine because it showed no leaks prior to this.

Do you still have braided hoses on the car?
If so could it be that the hose is leaking? The older ones crack
and the fuel can just leak out under the pressure.

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Ginny in Denver-ish
78 300SD, 265K (mine)

Yes I still have the braided hoses and thought they were covering electrical wires so I never inspected them for leaks. Are they plastic or rubber hoses inside? Perhaps one of them was cracked or has fractured from excessively cold weather.

Rubber.
As they age they crack under the braids. Hard to see cracks but if the hose is leaking it will be wet. Always good to just replace all braided hoses in the fuel system.

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Ginny in Denver-ish
78 300SD, 265K (mine)

Just wanted to respond back for anyone who may find this post in the future

It turns out that my spin on fuel filter's gasket had warped some how. One side was sticking up about 1cm and it allowed fuel to get through. The replacement cost was only $13 from Autozone. I still don't understand why it warped and why that Mahle filter only lasted like 6 months. But it doesn't leak period so I am a happy camper again

Tanks

Cool!
Love a happy, cheap ending!

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Ginny in Denver-ish
78 300SD, 265K (mine)