23.5", perfect fit on the 603 radiator.

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CENSORED due to not family friendly words

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.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Got a little news, guys... I can't swear to it until after I run it into town tomorrow evening, but a test run this evening with the thermostat from the 104 out of my 93 300E parts car seems to show a drastic improvement. I drove several miles at 60mph and then stopped. Temp yesterday shot above 100C in seconds. Barely touched 100 this time, and then after idling for a timed 4mins with the AC running at 72F setting when I immediately pulled off the highway to simulate a long traffic light. Less than a mile of 35-40mph brought the temp back to around 90C.

It has never come back down that quickly or crept up so slowly since the serious heat set in here in Alabama. I have been forced to shut off the AC at any traffic light to keep it under 110C and it was rare it dropped below 95C when I started movung again.

I didn't think to measure and compare the fine details of the two thermostats, but they were slightly different. The one I took out has "BTT/BTO Made in Germany" around the top of the body. The bypass plunger has "2.466 87 L6" stamped on the bottom. The plunger that closes the bypass port is 1.694" in diam and measures 1.125" from the bottom of the flange to the sealing surface of the plunger. The bypass port is 1.300" below the flange, so the plunger only moves 1.175" to close the bypass. The spring on the bypass plunger is VERY stiff. I think the thermostat is opening until the plunger seats on the bypass and then can't compress that spring enough to open further, restricting flow from the engine into the radiator.

The thermostat from the 93 had a noticeably smaller diameter plunger and it seemed shorter, so perhaps lets the thermostat open further when hot.

It will be wonderful if the solution is this simple. Will report back soon.

Please do! I just looked on my maintenance doc and I am currently running a Behr 87C from 2014, so its 4 years old and has 50k on it. I am tempted to go buy a new thermostat, but I may hold out until you report back before purchasing to see if a later thermostat works better.

We can eliminate the fan clutch because if the cluthc was the issue, as soon as it engages and "roars", temps would drop fast, but on my 300TE it does not. It just stops it rising further, but never cools it down enough.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

I never had good luck with the current generation of Behr clutches, not just MB limited. They are junk for BMWs too. Sachs set me back nearly $200 for the M103, but guess what? Works as designed.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Yup, I put the clutch from the 93 on my car, too. The fan cannot be stopped with a rag at idle when the engine is hot. The electric fans are operating correctly, too. It's something to do with the coolant not circulating and the thermostat is the only obvious obstruction in the system for the pump to overcome. If the thermostat isn't opening far enough, it would act exactly the way we are seeing.

Which Behr clutch have you guys used? There is a Chinese made one and a German made one. The German one is much better quality though idk if it locks up as well as the Sachs.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.

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.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

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.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

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.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

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.

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CENSORED due to not family friendly words

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.

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1990 190E 3.0L