1976 300D / W115 / OM617 - Mercedes-Benz Forum

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post #1 of 6 (permalink) Old 09-24-2015, 07:12 PM Thread Starter
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Date registered: Sep 2015
Vehicle: 1976 300D
Location: San Diego, California
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1976 300D / W115 / OM617

Hello guys, this is my first post to the community!

About six years ago, when I was 14, I gave my mom $1,000 to find me a first car. She picked me up from school in a vintage "baby blue benz" - as I call it. I absolutely lost it and fell in love with european cars instantly.

After weeks of searching for the best mechanic we could, we finally found a Russian gentleman that worked for Mercedes-Benz of USA building AMG engines, and now runs his own shop (works alone) with his wife.

Just a few months ago I took him up an a great opportunity - to work along side him! I am now working with him several days a week, before my evening college classes. I can't even put into words the amount of information I have soaked up in the past several weeks. It's just me and him - and we get along great!

I have a couple simple questions:

1: He has been telling me literally every day I show up that I need to put some sort of additive in my fuel tank every time I fill up. He always makes jokes about how bad he feels for my fuel pump, and all the mechanical parts that are being destroyed by low grade diesel. I feel the need to take this seriously, because I remember buying the last OEM fuel pump in my area/state/country - I forget.

2: I recently replaced my motor mounts which reduced the shaking by 90%, but I still notice a bit of a shake (my mom drives a 1978 300D, the W123, and it's literally silent and still in the cabin compared to mine). My boss tells me this is most likely due to my injectors, since my motor mounts are brand new OEM. He gave me a special injector cleaner from Germany and told me to fill up a tank with it and drive 2-3 hours straight at 60mph. Still trying to find an excuse to make a trip from San Diego to Santa Barbara...anyway, what do you guys think? I'm sure its worth a try, but I would like to get your opinions before I put that kind of miles on it and burn that much fuel (cash).

3: Lastly...as clean as my paint is, there is ONE spot at the very very back of the driver side, the very bottom panel behind the rear tire. It's nearly rusted through - could probably break through with my thumb if I really tried. Again, my boss suggests we find that panel off a donor and literally just weld it on top, and sand it flush. I have seen his welding work on his personal vehicles, and where there was two layers of metal he had three. It looked as though nothing had happened. Though, I am worried finding a panel might prove to be nearly impossible. Anyone have luck doing it with bondo?

Anything is much appreciated! Hope this post wasn't too grueling!
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post #2 of 6 (permalink) Old 09-25-2015, 06:37 AM
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Date registered: Oct 2012
Vehicle: 68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
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Welcome. An Italian tune up cant hurt. Drive the thing hard could help.

The w114, w115, w116 are notorious for rust. what you see is the tip of the iceberg.

your Russian friend may be exaggerating things, AMG engines are only built in Affalterbach Germany.

His idea of rust repair is some of the worst advice I have ever heard. You are inviting the rust monster to continue to consume your car with the poor idea of sandwiching the rust into another layer. You need to cut the offending metal out and then weld the new piece in it's place. There are plenty of utube videos on how to do this. Your dime size hole will be much bigger once you actually poke all the rust out. for a small repair, just buy some sheet steel and make your own patch panels.

This guy sells a product to encapsulate rust that could be used on small areas. https://mercedessource.com/problems/...den-rust-spots.

This long thread will show you an extreme length to de-rust a W116. 6.9 #521 Restoration This guy has done it right!

Whatever method you choose, do not take your friends advice.
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post #3 of 6 (permalink) Old 09-25-2015, 11:22 AM Thread Starter
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Thanks for the great info.
Sorry I should of expanded the rust procedure a bit - of course he intends to remove the rust and put a layer of a rust prevention material in between the old and new surfaces.

How about the diesel fuel additive? Anything I need to worry about concerning my mechanical parts and sulfur?

Thanks again!
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post #4 of 6 (permalink) Old 09-25-2015, 12:50 PM
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Vehicle: '72 250C, '74 280C, '85 500SEL, '81 300CD.
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Using a Cetane booster is a good idea. Don't overdo it but you'll definitely notice an improvement in smoothness and noise.

The Stanadyne is a good product. I have used the Power Service line and liked the result.

The old school way of adding a quart of ATF to a tank of diesel works to an extent.

The W115 chassis is completely different from the W123. The W123 was designed for a lot more comfort and modernization than the W115. More detail was put into areas such as sound deadening, engine noise and personal comforts. The W115 will never be as quiet as the W123, even with the engines off.

Last edited by Mike D; 09-25-2015 at 12:57 PM.
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post #5 of 6 (permalink) Old 09-25-2015, 03:59 PM
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I'm still not buying his idea of sandwiching metal layers. For as much work as his methods would be you could just do it correctly. It really isnt all that difficult to do. Cut out the offending material section and then weld the new metal in. It is very easy to form a small piece of sheet metal with a body hammer and dolly.

Putting another layer on, regardless of any such "rust prevention material" would still change the body lines and leave a lump wherever it was done. I t would remain a trap for future water collection also.

I would recommend the mercedessource miracle paint method far over your friends idea if your hole is indeed small. However I would believe that your dime size hole is really going to end up much larger once you actually see what is there.

Here is what my dime sized spot on my 6.9 W116 looks like now after I poked at it a bit.
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post #6 of 6 (permalink) Old 09-25-2015, 05:18 PM
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Vehicle: 1972 220 D, 1974 450SL, 1995 E300D 2002 S430, 1976 300D, 1986 SDL, 1982 SD
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There are a few fluids that help make the car runner gooder.

Diesel Purge is going to clean up the crap in the engine. Lubro Moly makes a few other good things for the car. There are some standard diesel additives you can snag at the gas station. Cetane boosters are good, but using Biodiesel blends in the 5-20% range will really clean up the engine and fuel lines, while also quieting the engine noise. A half gallon of canola in the tank should not make a mess the way SVO does.

Being in San Diego, you should not need a winter treatment, but kerosene in this car will dilute the cold weather clogging. Change your fuel filters to increase fuel flow. Tank screens should be checked as well. Refresh your rubber lines too.

Shaking engine may not just be the engine mounts (DO NOT USE URO) but the transmission and front mount as well. Noise in the cabin can be ameliorated by using Dynamat or other dense padding on the floor side of the firewall. Put a hood pad in and put some dynamat in the door skins. Undercoating will help absorb noise and reduce the resonance.

As for injector or engine shaking, the Injection pump should have resolved most of that. If you can tell the engine is bouncing around while you look under the hood, you have bad mounts. If the motor sounds like a cat purring, you have a fine engine. Take it for a long hard drive. Look for steep hills to climb at WOT. This is an italian tune up. Black smoke and minor explosions while the coke is blowing out the tail end will tell you it is working. If you can go full blast on the freeway, speed limit all the way, your drive to Santa Barbara will help.

Diesels are made to go hard, for miles, not puttering around town on short trips. Drive it like you stole it when possible and do long trips of 60 miles at speed every few months.

The rust repair is really simple. CUT THE RUST OUT. then weld fresh metal in. Covering it up will not help, but may look nice for a few years while the rest of the car is eaten by rust
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74 450SL - Froggy
'02 s320 - Victor
'86 300SDL - Polei
'82 300SD - Allen

Retired cars
'76 300D - Voldemort
'95 E300D - Cleo
'72 220D - Gump
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