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Old 02-27-2003, 10:20 PM
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Diesel Leak & Some Smoke W123

I have just bought a 1979 300CD. Overall I'm very happy with the car, but I have found two problems.
I have found that the car leaks diesel, especially when I apply pressure to the gas pedal. The car also leaks a little when it is simply parked. When parked a small puddle forms behind the rear right hand tire. I have discovered a trail of diesel on the side of my car leading from the fuel tank door to the bottom of the quater panel on the outside of the car. When I open the fuel door, the area inside is always wet. I have also found a small trail of diesel fuel on the right side of my trunk. This trail starts near the location of the fuel door. Please reply with any comments on this problem.

My second question is whether or not smoke is normal when accelerating in diesels. The smoke coming from my tail pipe is gray/white in color, but is not visible when the car is simply turned on. Please reply with suggestions on how to reduce or eliminate the smoke.

NOTE***I would also like to add that the oil pressure is always at its max whenever there is any level or pressure applied to the gas pedal. With no pressure added to the pedal, the meter needle drops to about the half-way point on the meter. Is this normal?****

Thanks in Advance,
18 years old
(Student/ part time employed)
Los Angeles, California, USA
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Old 02-27-2003, 11:18 PM
jbaj007's Avatar
Registered User
Join Date: Jun 2001
Location: Santa Monica, CA
Posts: 2,053
The Diesel Discussion Forum loves these problems. Probably get more response there.

1.) Get a new fuel cap gasket first and then you can go from there. Trace fuel lines to rubber connectors, fuel filler vent line, etc.

2.) Some smoke is usual, but probably not ideal, unless at full load. Italian tune-up, IP timing, check chain stretch, Diesel Purge injectors, etc.

3.) Oil pressure should be doing exactly what yours does.

Really like the looks of a 300CD. Congratulations on your new car!
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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Old 02-27-2003, 11:41 PM
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Thanks for the comments, I'll try to replace the fuel cap ASAP, and check the other parts you commented on, Thanks
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Old 02-27-2003, 11:54 PM
Holson Adi's Avatar
Registered User
Join Date: Jul 2001
Location: Boston, MA
Posts: 2,561

Yes I agree, get a fuel cap gasket first. However I think you have to make sure you get the right gasket for the right fuel cap.

They have a new style cap now to differentiate it from the oil filler cap. Mine was leaking in the same way and I just bought the new style cap and it's been good ever since.

Some smoke...

since you just got the car.
do the following:

Adjust the valves and while the valve cover is off the engine check the timing chain stretch - a good independent should know how to do this. I had the MB dealer do it for me. They also replaced the valve cover gasket (should be done)

Change the oil and filter, brake fluid, AutoTransFluid and filter, air filter, and the two fuel filters.

Run a can of Diesel Purge (it's Lubro Moly's Diesel Purge) at full strength. I got mine from Performance products and it came with a nice set of instructions and tubes to do this.

Check your brake lines for corrosion (probably not a big deal in CA), check the condition of the pads and rotors (if the pedal pulses the rotors are bad)

That's all I can think of right now!

Enjoy the TRUE coupe (pillarless )
2008 BMW 335i Coupe
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Old 02-28-2003, 10:43 PM
fz500sel's Avatar
Happy now in paradise!
Join Date: Nov 1999
Location: Venice, FL - "sharktooth capital of the world"
Posts: 712

Welcome to the MB diesel gang. Those previous posts are right on the money.

After having your valves adjusted I would invest in some RedLine Diesel Fuel Catalyst. You can usually pick it up at the local PepBoyz. You don't need alot but I would start with 1 full bottle for your first couple of fillups. I firmly believe that you will notice a substantial decrease in your smoke. Also you should notice an increase in power.

All of the diesels do have the built in James Bond smoke screen feature. It's perfect when on the expressway and the guy in the convertible is on your tail. Just slow enough to let him get a good whiff of the diesel and then....floor it. He will get the James Bond smoke screen and you wont have to worry about him tailgating you again. hehe
85 300D 310K (sold)
90 350SDL 184K sold
83 300D 118K (sold)
88 300E 153k (sold)
93 400E 105K (sold)
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Old 03-02-2003, 10:34 PM
Posts: n/a
**********IT WORKED

I first replaced the rubber seal around the nozzel of the tank and put in a new fuel cap. And no more leaks. I've concluded that the diesel was escaping through the fuel cap, the diesel then passed through the old rubber seal (Which was old and cracked) and followed the nozzel of the tank into the trunk, and that's why there was diesel in my tank.

Total Cost to Fix: $6 (Fuel Cap & entrance to wrecking yard for rubber seal)

Thanks for the comments, you have saved me plenty of diesel.
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