Friends,

I bypassed the fuel thermostat in my new acquired 1986 300SDL to address a fuel leak. I completed the bypass and didn’t notice any leaks when I ran the car for about 5 minutes. After a 30 minute drive, I saw some smoking from under the hood. Sure enough, fuel was in the same area it was before. I’m going to change the delivery valve orings but was also considering the life pump and IP o ring. Are these common causes of leaks? I plan to own this car until the world ends, so I’m willing to just replace all possible leak causes. What do y’all think?

Don't guess. Look. It should be pretty obvious where the fuel leak is. If you have smoke, it's probably the rubber return lines on the injectors dripping down the side of the head.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

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

I see wetness from the front delivery valve, but it doesn’t seem wet enough to warrant pool on mount arm by the small shock. If other areas are common for leaks I’ll change them in a preventative effort. Smoke is coming from bottom of the engine. Nothing wet by injectors. The small hoses are fine. I’ll do the delivery seals and we’ll see how she looks.

Good Advice. I'd assumed that my ip needed dv seals (based on smell of diesel standing beside the car... and coming through the vents). Took a close look at the ip, and the only leak it had was a little oil from the stop lever. Looked at the top of the engine and 4 of 5 injectors had a wee bit of wetness around them. Flexed one of the return lines and it cracked open... spent the next 45 min. swapping out the return lines. They "looked" fine but were a dry-rotted mess.

Pro-Idiot-Diesel-Repair Tip - change the return lines while the engine is hot. /sarcasm

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1991 300D 2.5 "Rocinante"
2002 Golf TDI "Teen Spirit"
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1984 300D
1966 Mustang I6 3sp
1985 Mazda RX-7 GSLSE
1982 Toyota Supra
1977 Datsun 280z
1971 Datsun 240z