This is one of the first things you will perform when learning to DIY your car. Changing engine oil is easy and satisfaction is high when you know you performed preventative maintanence. Regular oil changes on the 617 engine will literary make it run forever and ever and ever and ever and ev….. until diesel is forbidden.
If you drive in harsh conditions and only doing short trips, you should change oil more often than 10.000km, if you are living in the flat lands and only doing long drives on highways, then every 15.000km might be enough for you. I recommend every 10.000 especially dealing with these older cars where engine wear is more prominent, also easier to remember than the other numbers.
Buy some engine oil, you will need 6.5 liters for the non turbo 617 engine. Determine which condition you need to drive your car in, hot or cold weather. I will do a short introduction to oil “weights” which are the numbers you see indicated on the oil can. Also decide if you want to use fully or part-synthetic oil. While modern cars normally use fully synthetic oil, these older Benz are actually made for using part-synthetic oil. However this is up for preference, I won’t discuss which one is better. On my part it seems that the fully synthetic oil is easier leaking out of gaskets than the part-synthetic one, but I cannot confirm this. I have used both types for the 617 diesel.
The numbers tells about the viscosity of the oil at different operating temperatures. The higher the number, the higher the viscosity. Low viscosity gives less friction, but don’t give as much lubrication. Usually you will see a number like this: 5-40
The first number indicates the viscosity when the engine is cold, while the second number indicates the viscosity when the engine is warm. To ease startup the engine oils are engineered to give less friction when the engine is cold and it will start to thicken when the engine comes to operating temperature giving better lubrication.
The handbook in your car will tell the recommended viscosities at different ambient temperatures. The higher the viscosity on the the second number will make the oil more expensive, race cars have up to 50 and 60. If you choose to have 40 it is more than good enough. Living in cold Norway where temperatures can drop below -25°C easily I used 5 viscosity on the first number which made startups easier on the battery.
So to sum up the preparation you will need:
- Engine oil
- Engine oil filter and filter gasket
- Oil collector
- Paper towels
- Basic tools
Oh and don’t wear your fanciest white pants and shirts for this job!
Have paper nearby in case of spills, plastic gloves are smart unless you want to look like a real mechanic while going to your desk job the day after (actually for the rest of the week). If you are agile you don’t even have to jack the car up for draining the oil out, the W123s have a good ground clearance and you have room enough for a low oil collector under the pan. Have a 13mm socket ready. The engine should be warm while doing the oil change so more of the crud will come easier out.
Start by removing the oil filter cover. Wait with removing the oil filter itself unless you want oil all over your engine.
Unscrew the oil pan bolt. Keep in mind that the oil will come shooting out at you and it will be warm, be careful not burning yourself. Also hold on to that bolt so it don’t fall into the oil collector. Let the oil drain for 15-30 minutes until it completely stops.
Remove the old oil filter, try not to spill oil all over the engine bay, protect with old rags. Watch if more oil comes out of the oil pan, I usually wait another 10 minutes.
Reinsert the oil pan plug now before doing anything else so you won’t forget it! I laugh every time when hearing about stories where people have filled up new oil and it just runs straight through onto the ground again because they forgot the oil pan plug. Take care not to over tighten the bolt, use only 40nm of torque, there is a copper washer there to seal, replace if it’s lost. Also clean the underside of the pan for oil. So you can more easily spot leaks later.
Insert new oil filter. Replace the oil filter lid with a new gasket that follows the new filter, put a thin film of the engine oil on the rubber gasket. Tighten the the filter lid. It is not necessary to tighten this much at all, just enough so the rubber seal sits nicely.
Open the oil filler cap and pour 5 liters of new engine oil into the engine. It’s good to use a funnel unless you are a pro at pouring into small holes. Wait a couple of minutes for the oil to collect in the oil sump. Then start the engine and let it run for 1 minute. Check the oil level, pour up one liter more, check the oil level again. If not full, pour up the last half liter while checking the dipstick not to overfill. If there was some old oil left in the engine the maximum capacity of new oil i less than 6.5 liters, there is also residue oil in the oil cooler.
Clean up your mess, pour the old waste oil into the empty cans from the new oil you just poured into the car. And check under the oil pan for leaks again. If no leaks take a short trip to see if engine is running smooth. Then after the little trip check the oil pan for leaks again and check the dipstick for oil level, if not completely full, pour a little more of the new oil into the engine until full.
That saved you lots of money on workshop bills. Workshops tend to overfill a bit too which is not recommended. Your level should be under max, not over it.