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Old 08-17-2008, 12:23 AM
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1978 300D...major problems, suggestions?


i just purchased a 1978 mercedes 300D with a custom turbo. the car has 150K on the odometer and is in fantastic condition. it has undergone a svo/biodiesel conversion at lovecraft biofuels in los angeles where i currently reside. i took the car to a mechanic that the previous owner recommended to discuss the air conditioning being upgraded and have the engine decarbonized. long story short he said the motor needed to be rebuilt. as a result, i decided to take the car to another garage "german independant" in los angeles to to get the compression tested and try and disproved the prior mechanics diagnosis. the second garage said there is no compression in the #4 cylinder, the impeller on the custom turbo is shot and leaking oil into the engine, the head gasket is leaking and the manifold is full of holes adding to my woes. the total cost of repairing and replacing these parts is between 5000 and 6000 dollars. i really like the car but i spent half of that amount on the initial purchase. i am considering replacing the engine, but i do not know if this process would yield the results that i desire or if it would cost less. i really wanted a durable car that would last a long time and one that i would be proud to own.

any input would be greatly appreciated.

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Old 08-17-2008, 12:41 AM
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Join Date: Mar 2006
Location: Mount Holly, NC
Posts: 26,274
troy, search for the terms lovecraft and lovecrap here... tons of reading on what that sorry conversion does to our beloved MB's.
best bet is to pull that crap off and swap in a good used turbo motor from a 300D 82 and up.
if you want to try and save the motor, I have seen good results by pulling the injectors from all the cylinders, and filling the pots with Marvel Mystery oil. letting it soak for a week or two. then spinning the motor over with the injectors still out to blast all the liquid out, then testing compression again. sorry to hear about the turbo issues, but custom and turbo are not often good words for the same sentence... especially if on a diesel motor that was not designed to have a turbo.
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
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My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
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Old 08-17-2008, 12:51 AM
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Join Date: Mar 2008
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After being through my own ordeal w/ a bad engine after a high initial cost, I would strongly suggest sitting down and doing a very thorough cost benefit analysis before you go any further w/ $$$.

you can get a reman engine from a highly regarded shop (Metric Motors in CA) for about $6k - $7k. Do not rebuild this engine if there is NO compression in one cylinder. Unless there is an incredibly forgiving reason like.. the prechamber is missing. If your engine has comprimised one of its pistons, its MOST LIKELY the end - cash-wise. Some times used engines show up, especially in CA. I have never bought one.

you said 'custom' turbo - that means the car did not originally have a turbo? You may have a cracked piston head.

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Old 08-17-2008, 12:57 AM
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Location: Long Beach,CA
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Before you test the engine compression again do a valve adjustment. As the valves wear the clearances get tighter and tighter. I could be a valve is being held open.

A Cylinder Leak Down Test might tell you if it is leaking from the Head Gasket, Precombustion chamber seal, Valve or Cylinder problem. In part of this test you will listen to here where the pressursed air is leaking from.

As one of the members stated the engine may not have been designed for a Turbocharger; that could be a source of the problem.

I looked up his engine;617.912 but do not know enough to know if it came Turboed.

yort might want to check his engine number to make sure what engine he/she has in the car (found stamped between the end of the Fuel Injection Pump and the Oil filter Housing at the top of the Engine Block).

The Diesel Giant website has a pictorial on where to find this number.
84 300D, 82 Volvo 244Gl Diesel

Last edited by Diesel911; 08-17-2008 at 12:33 PM.
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Old 08-17-2008, 01:20 AM
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I agree w/ 911. That is a solid assessment. I would like to imagine that a respectable shop would have gone a bit further to diagnose as he suggested. Did they say / do anything else?

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Old 08-17-2008, 01:30 AM
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the car was not originally intended for a turbo install, so problems stemming from the install would make sense. i believe benz did not begin releasing turbos until about three years later. the car currently runs, but im not sure how long it is going to last and i cant sell it for anything other than parts. unfortunately, i am not prepared to spend another 6000 to 7000 on another engine. in addition, it certainly makes sense to not rebuild if there is a compression issue with one of the pistons. it could just be a i ended up with a lemon...
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Old 08-17-2008, 01:37 AM
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the shop didn't say anything other than

-a lot of holes in the manifold
-turbo bearing set bad and leaking oil back into the engine
-head gasket leak
-no compression in cylinder #4
-glow plug relay bad

i had the first shop that i took it to decarbonize the engine because i thought that would improve the performance. other than that there has been no work done on the car.
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Old 08-17-2008, 08:46 AM
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At this point, I think a used engine is the best alternative. Although, if you can't install it yourself, you're still going to be into the car for a fair amount of $$ once you pay to get the engine installed. So, unless the car is pristine, it may not be worth it.
How long have you owned it and from whom did you purchase it? Did the seller install the turbo?
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 08-17-2008, 01:18 PM
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i have had the car for about 3 weeks. i bought it from a private seller who was very proud of its condition, although i don't believe that he had any idea of the actual condition of the motor. the person before him apparantly had the turbo installed. the car was handpicked as a purchase by lovecraft for the previous owner. i bought the car on the day that i initially saw it because these cars sell very fast and are renowned for their reliability.
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Old 08-17-2008, 05:54 PM
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Location: Nova Scotia, Canada.
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Stay with the ship just a little longer. It may just need a valve for example so do an air injection test to see where the air is coming out of on that low cylinder. Also since you paid for a compression check what where the other cylinders readings? Also was the low cilinder actually zero? You have to have that information first to determine if any effort is worthwhile in my opinion.

If the car was some kind of aftermarket turbo conversion does it have a line feeding from the top of the injection pump over to the turbo area? If it has a line from the top of the injection pump try following it to it's destination. If not there is a possibility the fuel was not enriched for the turbo so the engines additional strain might have been minimal. With what is almost general information in lovecraft circles anything is possible.

You have already apparently been paying shops. These cars are a learning project. Otherwise watch out for the poor house. You are much better off to learn to be self reliant on these cars. They are basically pretty straightforward in comparison to todays general offerings. So you can actually do what is required yourself.

Last edited by barry123400; 08-17-2008 at 05:59 PM.
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Old 08-24-2008, 11:05 PM
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i just wanted to say thanks to all those who responded to my post. i have decided on selling the car for parts and starting over before the spending gets out of control. after another week of driving, the car is continuing to get worse. i have settled on a 1985 300td that is in better condition and only after a thorough "check-up" with a new mechanic.

thanks again!
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