Yet another overheating question. I have a 91 350SD just purchased, going through it to get it drivable. I was told by my Mercedes shop guys that the car should NEVER get over 85. It hits 95 to 100 with in-town driving here in Texas. Gets down to 90 to 85 on highway.

I replaced the thermostat with an OEM one. Pulled the radiator, it looked great. And just put a Behr fan clutch in it. Both the aux fans work.

In reading the board, I see that others say it is ok for these cars to run hotter than 85. Normal for them to get up to 100.

But here is my problem. I just put the fan clutch in it, and even when the car slightly over 100 in temp, it doesn't engage. It simply free-wheels. Same as the old (original) one did.

So what is up? Does it not engage because it really isn't supposed to? Or maybe the radiator has some cold spots in it and doesn't get the clutch hot enough to engage? Anyone seen them do that?

Don

First question: - Is the temp gauge accurate? If it is reading high, the engine could be operating at normal temperatures. Either use an IR thermometer aimed at the head adjacent to the temp sender, or a thermometer in the top of the radiator, to confirm gauge accuracy

If accurate, you need to inspec t the Fan, which IIRC is a viscous clutch, with no RPM related features. It should not freewheel more than 2 turns when the engine stops if the engine temperature is >100'C.

You may also have a problem with the new thermostat.

Are you losing coolant? - low coolant will cause high temp.
Does the coolant look oily? Oily coolant may be due to head gasket leaking combustion gases into water jacket.
Does the engine oil look milky? Milky engine oil may be due to head gasket leaking water into sump.
I hope this helps - Tony

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

The temperature gauge is dead on. Confirmed it with Fluke meter and thermocouple probe.

The old fan and the new fan both do the exact same thing. When started cold they are viscous and whirl. After they get warm they pretty much free-wheel. After engine reaches 100 degrees, they still aren't engaged. I can shut the engine off and they continue spinning for 7 or 8 full seconds.

The old coolant I took out was spotless. Has new coolant in it now. The old thermostat was brand new, replaced it with yet another new OEM one.

My guess is the fan clutch isn't getting hot. Just because the engine is at 100 degrees doesn't mean the fan is getting hot. What I was asking if anyone had seen something like this, where the radiator possibly had cold spot in it and was keeping the fan too cool.

Don

My 350SDL did the same thing. Turned out the biggest difference made was replacing the shock absorbers on the idler pulley. The engine shake kept them very busy until they were changed. Afterward the idler pulley stopped bouncing which in my opinion allowed the water pump to run smoother and more efficiently. Never goes aboe 100 now.

I also had the radiator flushed to get all the calcium deposits out and then did the MB citric acid flush.

__________________
1991 350 SDL
183,000 miles

1982 240D
130,000 miles

Don,

I had my fan clutch replaced 2 years ago, no difference either. So I recently did the "refill" effort with the Toyota fluid. Net difference is 5-10* in most driving situations. Particularly running the AC, stop and go traffic, and when exiting the highway.

Prior to refilling, the clutch with spin for "one thousand, two thousand... up to 6" or longer after the engine was shut off.

With the refill, it now stops spinning in 1/4 to 1/2 turn of the engine stopping.

I may have over filled it, but I would rather have it working more of the time than not enough.

Chuck

What you describe is normal for a 603 engine. They run hotter than the 5 cylinder engines. 100-105 is normal you may want to check your antifreeze water ratio just to ease your mind . FYI the heads of these motors have had many design changes since they were first made. How does the car run otherwise fuel milage,power. engine noise. these engines are prown to bending rods. Do a search on 603 engines theres a huge amount of info that will help you in the future.

Good luck

I'm aware of the engine self-destructs many of the 350s had. This car has 200,000 miles on it, it has a lot of issues since the previous owner did NO maintenance. However, other than needing some injectors, the engine sounds great. Uses no oil.

I don't have full service history on car, however I'm betting the engine was either replaced, or got the updated parts. The valve cover has a big OE parts sticker slapped on the side of it, no idea why it is there other than it got replaced at some point.

Either that, or this is one of the "good" ones. I here there are 350 SDs out there that went 300,000-400,000 with no issues.

Don

__________________
1991 350SD 265,000 miles
1981 300D 320,000 miles

1990 350SDL 144,000 miles (wrecked)
1991 350SD 225,000 miles (sold)
1985 300D 113,000 (sold)
1987 300SDL 183,000 (sold)
1984 300D 360,000 (sold)

The visco fan coupling does indeed have to sense the temp increase before it will engage. To do this have a reasonable amount of airflow thru the radiator.

Have you checked the radiator and condensor for dead insects or leaf blockages? I'd suspect you are not getting enough airflow thru the radiator.

My 602 runs at a steadt 80C but it will rise to 90-100 in very hot weather with the A/C on in stop and go traffic.

First, what Tim said above is what you need to check. The fan clutch engages based on air temp and if the airflow is impeded directly in front of the center of the fan, OR the radiator has a cold spot there, it will never engage properly. Also make sure the fan clutch face & flat metal spring are clean and free of oily crud.

Second, your "Mercedes shop guys" are flat wrong. The car should run at 85-95C most of the time, and on very hot days (and/or climbing a grade), it may reach 100-105C but then drop back to 85-95 when the load is removed. Constant temps above 100C is not normal, but 90-95C is normal!! You may not even have a problem at all.

Third, I'm assuming you have a NEW fan clutch, the 606 clutch with the plastic fan blade. These clutches seem to have a much higher trigger temp than the old 603 clutch with the metal blades. On my car, when cool (or at temps at 80-90C, anyway), the fan freewheels a lot when you kill the engine - say 6-10 revolutions. When it's REALLY HOT outside, like 100F ambients, AC on max, dash temp gauge at 100C, it will stop within about 2 turns. But you still can't hear it "roar" when revving the engine, and it has to be really damned hot out to engage the fan.

Fourth, the old 603 clutch can be re-filled with silicone fluid, if the bearing is still good. However nobody has figured out how to refill the new 606 clutch - the problem is you can't remove & re-install the flat metal spring without distorting, and therefore damaging, it.



606 fan clutch face:

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

It is a new Behr clutch, clutch only - no fan. It did look like a newer design, so I assume your right, it is the 606.

I'm beggining to think I don't have a problem at all, it is just beyond me why the fan clutch is there because it really doesn't do anything. Unless I REALLY overheat the car, I guess.

Basically what do I need to do to refill the old clutch? What do I put in it and how much?

I am pretty sure the bearing in it was still good. I may give that a try and run it for awhile rather than the new clutch.

Thanks,
Don

__________________
1991 350SD 265,000 miles
1981 300D 320,000 miles

1990 350SDL 144,000 miles (wrecked)
1991 350SD 225,000 miles (sold)
1985 300D 113,000 (sold)
1987 300SDL 183,000 (sold)
1984 300D 360,000 (sold)

Don,

There are other posts with pictures on this as well... search might help. The short version is:

- most folks are using the Toyota silicon fluid. Part number is 08816-xxxxx. I used the 10,000 centistoke (sp?) version which is the thickest. There is a 6000 also. So the whole part # is 08816-10001. I ordered 2 18 ml bottles.

- loosen the fan shroud move it out of the way. There are 3 bolts linking the fan to the clutch. My bolts were loose enough I could use a screwdriver between the cooling fins to hold the clutch and loosen the bolts. Some folks use a c-clamp on the belt pulley.

- remove fan and shroud.

- there is one bigger bolt ( allen?) in the center of the clutch. You need an allen or a very stubby allen socket. MB sells one for about $4. You can now remove the clutch.

- There is a metallic spring on the front, with a rubber gromet and then a pin going into the clutch. This is the hole I used to refill.

- I went a drug store and got a syringe (very small) to fill through the small hole as recommended here. There were still some difficulties. The specific incantation I used was to:

* removed syringe needle
* open the syringe (pull plunger out)
* fill with fluid
* hold plastic end of syringe against the fill hole
* squirt in a small amount of fluid using the plunger
* the fluid would then slowly come back out, I would insert a small nail/brad and push down on a the spring material inside. The fluid would drain back in. This was in about 2ml increments.
* overall I probably spilled 1/3-1/2 of the 2 bottles of fluid.

My car is running 5-10*cooler and cools much more quickly when coming off the highway. It does seem as if the fan is "on" all the time. Given the choice I would rather have that than too warm.
Good Luck!

Chuck

On the road, summer or winter, 90-92C. In the city traffic with AC on, 99-103. My aux fan, per specs, only comes on at 105C. My O.M. states that it is normal for the temp to rise close to the red line in some driving situations. I wouldn't push that last statement, myself. BUT, that is what MB says. And I am assuming your temp. gauge is correct.

__________________
Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

gsxr - I just got through refilling the fan clutch on the 98 E300 I just bought. I pryed the metal spring out and it did not bend. I filled it with the 10,000 cst Toyota fluid and I don't recommend that. The fluid is too thick and the fan stays engaged all the time. I have ordered some 3,000 cst fluid and will try to drain the thick out and re-fill with the regular. I think the plastic blades require a thinner fluid than the metal ones in the S350.

__________________
1995 S-350
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD
1998 E300D
310K +
2012 E350 BlueTec
120K

Uh-oh. That's interesting. I got some 12,500 cst fluid but haven't used it yet. I think you're right about the plastic fan needing thinner fluid. Oooops. I'll make a mental note to use the 6,000 cst stuff if I ever mess with a 606 clutch!

Just curious - with the engine cool or warm (say, between 40-80C on the gauge), if you kill the engine, how many turns does the fan spin before stopping? I'm wondering how solidly engaged it is with the 10,000 fluid in there. Also you might want to try 5-6k, I think 3k might be a little thin...?

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

I would say less than a quarter of a turn. Pretty much instant. You can hear it roaring from inside the car at highway speeds even on a cool morning. There is some slip because I can hold the fan blades with a glove and have the engine started and can hold the fan but it grabbs. Once it starts spinning, you cannot stop it with a glove. I ordered a new one to use while I experiment with the old one. Probably will take a long time for the 10,000 to drain out. I am going to pull the pin and just let it set upside down for a week or so.

__________________
1995 S-350
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD
1998 E300D
310K +
2012 E350 BlueTec
120K