Hello, my name is Dave Larson and I just bought a 78 300SD in Denver. I am flying to Denver Friday night 10/12 to drive the car back to Detroit where I live. There are a couple of mechanical things which concern me and I hope you all can help.

My brother (a fairly decent mechanic, but with no MB Diesel experience) has been driving the car and informing me of potential "issues": (note that this appears to be a Euro model)

1. Heat doesn't work, have pushed water through the core and it is clear. The valve which is controlled by the climate control appears not to be functioning. Is there an easy fix? Can that valve be disassembled and cleaned? If not, I plan to bypass that valve, installing a mechanical hot water valve in the line just to get me home.

2. At one of the injector-to-head junctions there is a fuel seepage. Nothing big, but can this be easily repaired before the cross-country trip? What parts and special tools are needed? I would have to get those overnighted to my brother in Denver unless the Stu Ritter MB shop has them. Speaking of Stu Ritter, anybody have any input on that outfit?

3. Motor mounts appear to have collapsed (like they had in my 944 Porsche). I plan to replace, but will it be OK to drive in it's current state? This should be a low-load, low-impact trip.

Thanks in advance for your suggestions. I look forward to talking with you all, for some time I have been a member of Rennlist ( a Porsche / BMW discussion group / website) and I am a serious racing guy. I have a 1.9L 67 VW Bug I drag race, ran a 10.90 et at 122 mph this past weekend. 1 drag race VW, 1 slotcar 944 Porsche, 1 Mercedes. Have had many Porsches and Volkswagens, this is my first Mercedes.

Have a great day! Dave Larson

1. Climate control valve is not fixable. It must be replaced and they cost about $400. If you intend to keep the car for a long time, I suggest you replace it. You will have to bypass the climate valve and it will be difficult because of how the hoses are connected .

2. I don't quite understand what you mean by head-to-injector junction. Check the fuel return lines that go from injector to injector. That is about the only thing that can leak in that area.

3. Motor mounts probably have been this way for some time so should make it home but they might cause a serious vibration.

P E H

Through reading previous posts on this Forum I thought the heater vavle was called the monovalve and that there was a repair kit available. (from FastLane) I paid $600 for this vehicle to use as a beater (albeit a very nice one), will not buy any $400 parts. Maybe we are talking about a different part, my brother forsees no difficulty in bypassing this firewall-mounted, solenoid-controlled valve mechanism using a longer, contorted piece of hose to go from the engine to whatever heater core inlet it must reach. Other forum posts mentioned the possibility that disconnecting the A?C compressor switch might allow the valve to operate. We're trying that, I don't need A/C, drive the Porsche in summer.
Why would disconnecting the A/C allow the heater valve to work? Is it a climate-control computer or relay issue?

On the injection, the seepage apparently comes from the area where the injector enters an insert in the head. This steel insert has slots which apparently use a spanner to tighten into the head. I am having my brother look again at the area to provide a more detailed description.

I plan to attempt the motor mount replacement myself when I get the car back to Detroit. Is there a mount replacement procedure somewhere in this forum?

Yours has been my only reply thus far. When that happens on the Porsche discussion list, it's because the newbie question has already been answered a million times and the answer is in the archve or FAQs. Is there such an area in this forum I should be accessing for this info?

Thanks so much for your reply, I really appreciate all the help I can get and look forward to providing the Forum with insight from my own er, "unique" perspective. Dave Larson

The search function is located at the mid-upper right of the screen. Sometimes it does take a while for some questions to get answered, not a slight though.

There is a difference between the 116 chasis and the 126 as far as the heater/climate control goes. The 126 has a monovalve (cheap/easy fix) while the 116 has an auxillary water pump and some leakage in that area can cause the control module to fry (or so I've read).

1978 puts it solidly as a W116. Try doing a search on the aux water pump, there may be some DIY fixes you can attempt (read: cheap and easy).

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Non illegitemae carborundum.

"note that this appears to be a Euro model"

From what I've read, the W116 SD is a US or North America only car. Not available even in Germany.

Motor mounts are not difficult to replace. Outside of the parts, you only need some hand tools (floor jack, piece of wood, 8mm hex bit on a long extension and 5mm hex key, sizes are approximate). I'd sure do it before a long trip.

Why not look for a used heater control valve? Who knows what else in the ACC system won't function if you bypass the valve?

Sixto
91 300SE
81 300SD

a 78 Sd is no drag racer but I'll bet you will be suprised at how comforable a long drive can be and how little fatigue you feel at the end of a long day at the wheel... have a safe trip....
William Rogers....

I do not see anything that should prevent it from making a long trip. The fuel mileage will suffer slightly because of the leaking injector but so what - resolve it when you get home.

__________________
Jim

Continued investigation and daily-driving road tests by my brother along with the help of listers' comments has pretty much convinced me that it's OK to drive the car home Denver to Detroit pretty much as it is. The fuel leak is very small and appears to be from one of the braided-fiber-covered rubber fuel return lines. I'm going to buy a section of that hose and carry it with me along with the classic "road tools".

Motor mounts cause irritating vibration only at idle, fine rolling under load. If heat doesn't work I'll just dress warmer for the trip if bypass of malfunctioning water valve proves impossible. I have a feeling the heater control valve is just stuck, the car sat for a long period at one time and it came up non-functional after that. All other climate control functions seem to operate just fine, even the A/C, which maybe needs a recharge to improve it's overall "coldness".

Will fix heat, install new motor mounts and replace any questionable rubber fuel hoses, belts and filters back home in my shop. I don't forsee any problems that will stop me. There is also a broken driver's side front window regulator "chassis", probably gonna need to scrounge one of those. The car looks very solid overall, though! Just seems like a heck of a lot of great machinery for the bucks and I have learned to be VERY handy with VWs and Porsches - why not this? I'll keep you posted.

Thanks again, please continue to supply heater repair tips.. 1978 300 SD. Dave Larson

You are right, the hot water valve is stuck but it is inside the climate control valve. I had 2 of them go bad in 2 different cars. One I replaced and heat works automatically to a set tempereture and the other one I replumbed it and put in a hand operated valve but it is difficult to adjust the temperature.
As far as the aux waterpump is concerned, it is only needed at idle to get enough heat in cold weather. System will work at road speed even if aux pump isn't working. Usually the electric motor in the aux pump burns out and the impeller does not rotate but the coolant still passes thru it.

The steel ring with the slots for a spanner wrench is what holds the pre-combustion chamber (PCC) in the head. The injectors screw into this steel ring. It is rare that the PCC have to be removed. You need a special puller to remove the PCC and the glow plugs must be removed first. The PCC are better left alone unless the head is being rebuilt.

P E H

For the motor mounts, you will need a 10mm hex (long) and a 6mm hex (short). Basicly the motor mounts are bolted to the crossmember by 2 6mm hex bolts. Then the brace coming off the side of the engine sits in/on top of the motor mount. A 10mm hex bolt goes through the bottom and up into the crossmember. You will need to loosen the bolts that hold the engine shocks in place, to raise the engine. Use a piece of wood under the oil pan as you jack it up, also loosen up the fan shroud so that the fan won't get caught up on it.

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