Even the smallest coolant leak will cause loss of pressure in the cooling system and elevated temperatures.
Check the coolant bottle for cracks - remove it and have a look at the back and the bottom.

Check the water pump and make sure there is no leak from the weep hole.

Make sure these is no leak back at the return heater hose at the back of the block (here's an extreme example)


Your water pump may not be up to scratch either.
Don't forget the coolant bottle cap - make sure it's holding pressure.
And another issue is the famous breaking radiator neck. These crack and break off at the point where the top hose joins the radiator. Take the hose off and see if there are any cracks. There is no real repair for this except a new radiator.

If the system is not holding pressure the fans are irrelevant

Injectors are cheap.

Don't forget the seals
These seals



Not these seals

I have always changed out the overflow tank when it gets that color (Post 16). Tells me that the plastic has changed properties and has become very brittle. And of course a new Benz pressure cap wouldn't hurt.
Anziani
'97 CL600 55K

The reason I suspected the fan clutch was that because on the highway the temps are fine, but exiting the highway the engine is heatsoaked and the fan isn't locking up to cool it. If the accelerator is pressed while in park the engine temp will start to go down.

The injectors plus seals have been on my list so that'll be done soon.

I have a new problem that has arisen, oil loss. I've changed the front timing cover seal but there's a lot of fresh oil that on the lower part of the block on the pass side ? where should I be looking next ?

Is the oil loss on the front of the engine or the back? Check the back of the engine on the underside of the cylinder head. Use a mirror and see if the back passenger side corner has oil spots or drips. M103's leak oil from the head gasket back there! if you smell burning oil while sitting idling in traffic that is a clue as well.

My 103 swings temp like yours does. Its what they do. After purchasing a Behr fan clutch and having it be locked up nearly all summer once the engine temp was high enough. I went the all electric cooling fan route. Mine works well but is not a cost effective route. Performance will depend on where you live too. Mine now takes much longer to swing up since airflow is better at idle. Your using MB coolant?

I agree with the injectors needing to be changed. They are not at all serviceable and you should change all the seals at the same time. My car just ran better after the swap. I still have a lumpy idle but its less with the injectors. Mine were changed because of stalling when coming to a stop.

__________________
Current
1989 300SE - Siegfried
2010 Toyota Tundra Crewmax
2005 Honda CRV

Gone but not forgotten
2001 F150 Supercrew - The Screw
1966 Ford LTD 390 - The Big G!
1995 Mercury sable
1986 Subaru DL
1982 Ford EXP - my first car

the oil loss in the front pass side, not the back. Just did a 500km trip to the cottage and lost about 1/4 quart or a bit more.

oil from that area is the timing cover plenty of DIY's on this. Replace the injectors with the good Bosch ones I made the mistake of trying the cheap ones and they were worse than my old ones!

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88 W124 3.0
96 R129 119eng
06 ML350
98 ML320 sold
02 CLK55 amg

I've done the easier(upper u shaped seal) and I found diys on that, but for the lower portion i haven't found anything.

Nvm just found Ps2cho thread, i have laundry list of things that need to be done now lol
Cooling overhaul
Rear suspension
Tires
Fuel injectors
Timing cover
vacuum lines
And i want to get some body rust taken care of !

I got myself a copy of Mercedes WIS off of E bay. Best investment I made as I have 4 cars. The lower timing cover is a bit more tricky and includes the removal of the upper timing cover,balancer,alternator,chain tensioner,all this while you do not damage the oil pan gasket! Oh and use the expensive sealant not any cheap stuff !

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88 W124 3.0
96 R129 119eng
06 ML350
98 ML320 sold
02 CLK55 amg

I had to do my front main seal on the crankshaft. Not as bad of a job as I thought it would be. You do need a large socket, torque wrench, and the adapter that keeps the engine from rotating. My timing case itself was not leaking since its sealed pretty well from the factory. My oil pan used to be wet and now its dry!

__________________
Current
1989 300SE - Siegfried
2010 Toyota Tundra Crewmax
2005 Honda CRV

Gone but not forgotten
2001 F150 Supercrew - The Screw
1966 Ford LTD 390 - The Big G!
1995 Mercury sable
1986 Subaru DL
1982 Ford EXP - my first car

OK, so update time,
Bought new Bremi spark plug wires and they helped the starts for a couple days but the misfiring symptoms are still there but not as bad as before, the worst is on hot starts.

Oil loss was due to using wrong oil(5w-30), switched to 15-40 Rotella and the oil consumption is now gone

New Behr fan clutch has been ordered and should be installed later this weekend, does anybody sell the MB lock rod tool?

While I'm doing the fan clutch might as well do the power steering filter, new drive belt and coolant flush.
What type of coolant is recommended?

Mercedes coolant and distilled water. But how old is your radiator? If it is the original, replace it along will all hoses. The car is 20+ years old.
Anziani

Agreed. Replace all hoses and use either mb coolant or xerex g05. Depending on your climate will determine the coolant/water ratio. If you are somewhere where the ambient temp is warmer year round then consider a 70% water 30% coolant or higher water concentration. Otherwise 50-50 would be good. I'm currently running straight distilled water and water wetter because temps here year round are around 80+. Do a vacuum test to check for leaks that cause misfire

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1990 190E 3.0L

According to the service history the rad, waterpump and hoses were all replaced in 2006. They still seem to be in good shape.
Lsmalley where and how do I do this vacuum test ?