Unfortunately my coolant ratio is 70:30 water to G05 and in 110F the clutch is engaged all the time and temps still stay there. No collapsing radiator hoses either.

How did the car run last summer? Did it have the same problems in the same kind of weather?

I recently chased overheating problems in my SL. Not a W124 and not a M103, but perhaps some of the same things apply here.

To make a long story very short, my issues were 2-fold:

1: Still had the original thermostat in it, MB logoed and everything. Unbelievable it made it 35 years, but it did. Original thermostat was still working, but would not open fully and would cause overheating (>100˚ temps) on a warm day, anything over 90˚F outside.

2: After replacing thermostat, car ran significantly cooler when moving but would still have temps creeping up in traffic or when idling in gear. Fan clutch passed the "shred a newspaper" test, but was replaced anyway as being suspect. With new clutch, heating problems disappeared immediately. It also makes a noticeable noise when the clutch engages and the engine is revved. I only bring it up because it may seem like the clutch is working properly but could still be slipping enough to reduce cooling capacity.

110F ambient is a challenging heat load. Could you use an infrared thermometer and shoot the temperature at the radiator inlet and outlet, then post back? I'm curious how much heat rejection you're getting under those conditions. It could well be that you're simply beyond the design point of the cooling system.

The viscous fan clutch should cut out at around 30 kilometer per hour.
After that speed the airflow through the radiator overcomes the clutch flow.

Last time I had your problem it was the water pump.
I put a erzatz non oem Behr pump (PRC knockoff) in the car - didn't get any better. Changed pump again for a Graf and all overheat problems disappeared. Car ran at 87 - 90 constantly even in very high ambient temperatures.
Fleebay knockoff cheap pumps don't cut the mustard - it's just one of those occasions you have to bite the bullet and get the real item

If you have a minute leak anywhere, the pressure cannot be maintained - the symptoms you describe can also become evident.

It’s completely normal.

The needle is not like American cars which basically don’t move unless you are overheating. You are totally within the operating spec of the car, despite extreme ambient temperatures.

If you simply can’t let it go, change your coolant mixture so that it’s mostly water, and remove your thermostat.

I'm not familiar with the M103, but if it's anything like the Mercedes V8's and diesels then removing the thermostat is a BAD THING. The thermostat does 2 things:

1: Allows circulation from the radiator

and

2: Closes the bypass port

If the thermostat is removed, the bypass port is always open and will be recirculating coolant through the block instead of through the radiator like you want it.

I thought you were running the r152a? My temps just recently were high like that on the freeway with a/c on with my electric fan set up (http://www.peachparts.com/shopforum/3746181-post28.html). I just recently went back to the viscous fan and my temps remain low ~85. What you can try doing is swapping out your thermostat for this one: [79°C Thermostat (MB p/n 1102000615)]
Even when idling and the a/c on (using r152a) the temp will creep up to about 105, then the aux fans kick on and the engine will stabilize at about 90 - 95 until I start moving again, then it drops back down to about ~85. Also, my aux water pump is still wired in to cut on at 91C, which may or may not help or make much difference while the car is on, but when the car is shut off after being at about 100+C, even for 5 - 10 mins, the temp is back down in the 80C range vs it being at about 115C when starting back up without it.

Because I'm running a 79C thermostat its hard to say if my temps would be similar to yours. Many many will agree that this is normal, even the mb engineers maybe, but we all know heat kills and I'd rather be running a little on the cooler side than hotter side. If you can, try to order a 79C thermostat and see if it makes a difference. I do not think there is any other issue with your cooling system as you seem to be pretty meticulous in making sure your parts are replaced.

Have been experimenting with my 300TE regarding it running what I consider abnormally hot. I know some are saying this is typical, but I don't buy it. I have NEVER owned another vehicle that ran in excess of 110C at any time unless it had a serious cooling system problem. The cooling system is either totally inadequate by design, or we are having some type of issue from an aftermarket part or other problem. When I was young and stupid, I had an old Datsun 240Z that the water pump locked up and wrung the fan off of. I put it back together without a fan and drove it that way in town for about a year. It was not much more different than this 300TE in terms of trying to keep it from overheating. That is NOT a good thing.

Here is what I discovered today. I believe the issue is with insufficient coolant circulation, as opposed to radiator efficiency or fan circulation. The radiator in the 300TE is nearly identical in size to the radiator in my Volvo 960 wagon, a 2.9L four valve, twin cam inline 6. The Volvo never runs more than 5 degrees above the thermostat temp, no matter the ambient temp, with or without AC running. That tells me the radiator should be adequate.

When I stopped today in a parking lot with it running at about 100C, I hopped out to do some other checks without turning the engine off. Just as I jumped out, the electric fans hit high speed, so I know the two speed fans are working. I used a rag and the fan clutch was delivering plenty of pull to the fan. I could not stop the fan. That says that the air circulation is as designed.

When I left the parking lot, it was raining pretty good. Temp was right at 100C by the time I got on the interstate a half mile or so later and ran in to a good heavy rain. I even got behind a semi to get a good spray on the radiator. The temp hardly changed, coming down to only 90-95C, at best. That cold water spray and drop to 75F in ambient temp should have dropped the coolant temp like a rock. Lack of it says to me the radiator and fan is not the issue. That obviously means that the cool water in the radiator is not getting properly circulated through the engine.

As I was getting off the interstate, I did one of my no fan tricks in the old Datsun and downshifted and coasted a half mile or so to the exit ramp. Temp dropped drastically. Closed throttle means no fuel being provided to the cylinders via the injection, so the engine is essentially air cooling internally. Same result going down a long hill a short time later. Again, saying the coolant has stagnated in the engine.

I really think there is a restriction of some kind in the system that is causing the water pump to fail to sufficiently circulate the coolant. Maybe the thermostat doesn't open enough and is restricting the flow. Maybe the water pump design is flawed and doesn't meet the needs in terms of flow and pressure to circulate the coolant.

I'm going to start with a different thermostat and see if it has any effect. Maybe the OEM thermostat has a larger opening than a typical aftermarket thermostat that meets the size and temp requirements? I am currently running a Stant thermostat I put in it about Feb, so it is new for all purposes. Does anybody know what the OEM Mercedes brand is? If not, I'll order a genuine Mercedes, but would rather not pay $50 for a $12 thermostat if I can avoid it.

On the om603 and om606 you can get a smaller water pump pulley to spin it faster. Maybe one is also available for the m103.

Just did a search and realized that you posted this same issue 3 years prior (http://www.peachparts.com/shopforum/tech-help/369583-smaller-water-pump-pulley-m103.html). I would think that unless you can remember a time when you had similar ambient temps and your car never made it past the 85-90°C mark while driving similar speeds then the issue may not be the cooling. You may want to check the tension on the belt, make sure you aren't running lean, and maybe even check to make sure there isn't rust. There must be something that's being missed. We've both had similar issues with cooling and I've also done several mods to the engine to help run it cool.

Psy2cho has a wagon which punches a much bigger hole through the air than the sedan. The cooling system is clearly undersized for his car in his climate.

Hoping my parts car has a MB thermostat, if so, will change this evening and report back.

Hell, I knew the 603s did...never crossed my mind to check the M103. :eek:

'A1042050210' is the PN from the EPC! Going to find myself one ASAP. More coolant flow and more airflow over that puny radiator is always welcome.

BMW did this with their M30 I6s. Went from a 144mm pulley to a 130mm pulley, about 0.5" smaller. It was optional for the Afrika Korps destined vehicles :D but became standard around 1989.



Like you, I still agree the radiators are too small in these climates. I remember another shop owner here telling me something similar about my W116 280S. The radiator was too small, even with the oil cooler. He preferred to remove the oil cooler and go with the larger radiator.

I think 1042050210 is just the updated part number, I don't think the size is any different than stock. I've ordered two as replacements, I don't remember them being smaller.

I just went through this. M104 wagon black on black in Tucson. Replaced the entire cooling/hvac system; Nissens radiator/condenser, Graf water pump, hoses, 82c thermostat, mb water switches, Denso compressor and drier+switches, evap, new spal aux fans, zerex 50/50. Everything. @110F my temps still went to 105f. What worked for me was replacing the new Behr fan clutch with the upated Sachs one.

Now even with super high ambients my temperatures never go above 95f even with the a/c running at idle. Incidentally I’m running r154a as well and getting 44f at idle and 36f freeway which I think is also helping as far as condenser heat dissipation.

Might want to check into the updating fan clutch or go the Spal electric puller way.