In my '87 300D, there is a device inline right before the lift pump. It also has a couple of fuel hoses that go up to the air intake (??).

The reason I ask is that I have an air leak coming from this device. I have replaced all my fuel lines with translucent polyurethane, so I can see the air bubbles. It happens mainly when I hit the throttle. The only fuel lines I haven't changed out yet are those two that go up to the intake. Is it possible that the device itself could be leaking air? Or is it more like these lines? Or maybe something at the intake?

Thanks

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1987 Mercedes 300D ~200K (Greasecar & Biodiesel)
1993 Ford F-250 7.3 IDI diesel 165K (Biodiesel)
1996 Thomas/International Bus with DT466 engine

I believe you are referring to the fuel heater, it uses coolant ("heatant?") to warm the fuel before it gets to the IP.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I agree, you're describing the fuel heater.

Yes it could be leaking but it's as likely to be leaking fuel out as air in. If you don't see some fuel leaks around the fuel heater then the air leak is likely elsewhere. There are a couple of rubber O-rings inside the heater that can be replaced but you'll probably need to get them from the dealer to be sure you get the right ones.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

Diesel Dan,

Not a lift pump, Its a fuel pump that pressurizes the fuel system.

A lift puimp is used on a carburated engine where the fuel is lifted to the carburator bowl and not pressurized.

P E H

A lift pump is also used on diesel engines where the fuel is lifted to the injection pump and pressurized.

It is a lift pump on the OM6xx engines.

Forced,

NOPE !!

P E H

Peh

Yep!!!

L M N

Noun 1. lift pumplift pump - pump used to lift rather than force a liquid up
pump - a mechanical device that moves fluid or gas by pressure or suction

All incorrect so far. This is the fuel thermostat, and it controls flow of fuel to/from the fuel heater (which uses coolant to pre-heat the fuel).

It has one o-ring and an internal copper washer that are replacable. Usually only the o-ring needs to be replaced to fix any leaking.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

I guess I'll replace the fuel lines going to and from the thermostat and the heater with translucent lines to see if the air is coming from the thermostat or from the heater.

Thanks!

__________________
1987 Mercedes 300D ~200K (Greasecar & Biodiesel)
1993 Ford F-250 7.3 IDI diesel 165K (Biodiesel)
1996 Thomas/International Bus with DT466 engine

you are all wrong...

It's part X-9870-echelon of the revised flux capcitor

What's a "flux capacitor"? Sounds like something on the Starship Enterprise. Does it alter the fabric of the time-space continuum?

__________________
1987 Mercedes 300D ~200K (Greasecar & Biodiesel)
1993 Ford F-250 7.3 IDI diesel 165K (Biodiesel)
1996 Thomas/International Bus with DT466 engine