Its almost become a yearly event for me to change the o-rings and crush washers since ULSD. They leak when it gets cold. Could it possibly be because the thermostat is open and the car doesn't get to operating temp? Am I not install or torquing them properly or is ULSD just that hard on them?

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My Daily : 96 E-300 Diesel with 195,000 miles
Retired: 92 300D 2.5 T 345K miles and for sale
Retired: 95 E320 157K miles and currently parked with blown engine

Both retired cars are for sale as is my w124 shop inventory

General consensus is the orings harden and deriorioate due to a change in the chemical additives in the different fuels. Once new orings are installed that issue should be resolved until super duper ULSD fuel arrives. I installed buna rubber orings in mune just after ULSD came out and haven't had any other problems. Viton orings are also available which I've used on every other fuel system oring on my engine; again with no further issues.

Guessing your orings are SAE rather than metric, crush washer are incorrect, that there is a torque problem or combo of those issues. Torque is 30, slacken, 30, slacken, and finally 30-35NM or 35NM one time only. The latter is supposedly the revised procedure. Both methods seem to work.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

member JA Davis will sell you a "Kit" that includes almost all the Fuel System O-rings in Viton.
Do it once this last time and be done with it.

http://www.fryerpower.com/store/page14.html

You know about being careful not to disturb the DV s themselves?

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'84 300SD sold
124.128