617 Engine- Strange Combination of Problems

[aldaeron]

I have a 1980 300TD Wagon with the 617 engine (non-turbo).

While I have been researching some of the problems I am having on the forums, I am posting just in case these three problems have some overlapping single fix.

My three problems are:

1) It does not start easily. It requires quite a bit of cranking (2-3 thirty second cranking sessions at full throttle). When it finally starts there is a large cloud of black smoke.
2) The engine temperature is significantly hotter. It is typically at 60-80 C and now it at 100+ C after 15 ish minutes of driving
3) The transmission shifts very late and very hard.

Some vehicle history (it is a little hazy - I got married 2 weeks ago and the Benz has been sitting for a little while)

I have been running the car on SVO. This is clean, new (expensive) Soybean oil from Costco. When it first was having trouble starting, I filled it up with Dino diesel. I estimate the tank still has ~ 25% SVO.

I live in Colorado. The summer was nice and hot and it has cooled down a bit recently. I don't think it is enough to affect starting the car.

I have done an "Italian Tune Up" within the past 6 months with 2 cans of Lubro Moly.

I have a number of filters in place for the SVO. They are all new.

The oil and filter were changed recently and the oil level is ok.

I had a local diesel shop do my valves about 3 years ago, but only 1500 driving miles ago. They also adjusted my transmission to make it shift smoother. I am hoping to not have to pay them for their expertise again.

I have a rear boost pump and heater to help with the SVO. (https://**************.com/node/2133 & https://**************.com/node/6310)

The glow plugs are new and the chamber were reamed with https://**************.com/node/2842. After replacing them the car was still running fine.

Around the time things started going downhill I made a few upgrades that I believe may have caused my problems:

1) I replaced the two fuel lines that attach to the fuel filter housing. One is from the manual lift pump to the fuel filter and the other is from the fuel filter to the injection pump. I also replaced the stock manual lift pump with a beefier metal one (https://**************.com/node/4773). I did not change the soft washers when I changed these components. I did not over tighten them - I was carefully increasing the torque with a crow's foot wrench until the leaking stopped. I fear that dirt may have gotten into the fuel line. I have seen other postings for cleaning the filter and pressure relief spring in the injection pump so I will look into that next. I have a CD with all the original factory manuals so I hope I find the correct procedure in there.

2) I was worried that the water pump belt was slipping so I checked the belts. Turned out the compressor belt was missing! I replaced and tightened all three belts per the manual. Like many old W123s I have a fault Climate Control Module. It is next on my list! I fear that the compressor/climate circuit may be causing some starting or overheating issues.

I am also aware that tight valves can cause difficulty starting so I am adding that to the list as well.

Thanks for reading such a long post. I appreciate any advice. The car was really working great about 2 months ago and I miss driving it.

-matto-